book of abstracts - sea level and climate research...

Global and Regional Sea Level Variability and Change

Palma de Mallorca, June 10-12, 2015


Book of abstracts GLOBAL AND REGIONAL SEA LEVEL VARIABILITY AND CHANGE



Contents Keynote speakers ..................................................................................................................................... 9

Sea-level changes during past centuries reconstructed from salt-marsh sediments. Prof. Roland

Gehrels, University of York, UK ............................................................................................................ 9

Considering vertical land motion in understanding sea level change. Prof. Guy Woppelmann,

University of La Rochelle, France ......................................................................................................... 9

The time-mean ocean dynamic topography: How well can we measure, model, and understand it?.

Prof. Chris W. Hughes, National Oceanography Centre, UK .............................................................. 10

What are the challenges facing quantifying impacts and adapting to global sea-level rise?. Dr. Sally

Brown, University of Southampton, UK ............................................................................................. 10

Semi-empirical modelling of sea-level change. Prof. Stefan Rahmstorf, Postdam University,

Germany ............................................................................................................................................. 11

Sea level variability: from surface gravity waves to mean sea level. Prof. Charitha Pattiaratchi,

University of Western Australia, Australia ......................................................................................... 11

Modelling historical and future mean sea level change. Prof. Jonathan Gregory, University of

Reading, UK ........................................................................................................................................ 12

Status and challenges on sea level monitoring and forecasting in the Mediterranean Dr. Begoña

Pérez Gómez, Puertos del Estado, Spain ............................................................................................ 12

Paleo Sea Level....................................................................................................................................... 14

Oral Presentations ............................................................................................................................. 14

Holocene relative sea level changes in the Baltic Sea basin: syntheses of geological and

archaeological data. Alar Rosentau .............................................................................................. 14

Sea-level highstands in Mallorca during the last interglacial. Thomas Lorscheid, Paolo Stocchi,

Alessio Rovere, Lluís Gómez-Pujol, Bas de Boer, Thomas Mann, Hildegard Westphal, Joan J.

Fornós ............................................................................................................................................. 14

Late Holocene sea-level change in the Falkland Islands: testing the Greenland melt hypothesis.

Newton, T. L., Gehrels, W. R., Daley, T.J., Blake, W. ...................................................................... 15

Posters ............................................................................................................................................... 15

Decoding sea level changes during the MIS 5 by means of Phreatic Overgrowths on Speleothems

(POS) research in coastal caves of Mallorca (western Mediterranean). Joan J. Fornós, Àngel

Ginés, Joaquín Ginés, Francesc Gràcia, Yemane Asmeron, Bogdan P. Onac, Victor Polyak, Paola

Tuccimei ......................................................................................................................................... 15

Fossil corals and speleothems as markers of past sea levels: towards a consistent global

respository. F. D. Hibbert, E.J. Rohling, P.M. Chutcharavan, A.Dutton, F. Williams ...................... 16

Vertical Land Movements ...................................................................................................................... 16


Combination Results of the Tide Gauge Benchmark Monitoring (TIGA) Analysis Centre Re-

processing Products. Addisu Hunegnaw, Norman Teferle ............................................................. 16



Models of land uplift in northern Europe. Holger Steffen ............................................................. 17

Relative sea level history during the Holocene and models of the glacial isostatic adjustment

process: constraints from the regions of forebulge collapse. Keven Roy, W.R. Peltier ................. 17

Posters ............................................................................................................................................... 18

Updated GPS vertical velocity field at tide gauges: application to global and regional sea level

change. Médéric Gravelle, Alvaro Santamaria-Gomez, Marta Marcos, Phil Thompson, Guy

Wöppelmann .................................................................................................................................. 18

Using InSAR to monitor vertical ground motions in coastal cities. G. Le Cozannet, D. Raucoules,

G. Wöppelmann ............................................................................................................................. 18

GNSS reflectometry for tide gauge levelling. Alvaro Santamaría-Gómez, Christopher Watson,

Médéric Gravelle, Matt King, Guy Wöppelmann ........................................................................... 19

Leveling for the altimetric control of tide gauge sensors and GNSS permanent stations in

Barcelona’s and Ibiza’s ports. Tapia Gómez, A; López Bravo, R; Gili Ripoll JA; Martínez Benjamín,

JJ; Pros LLavador, F; Palau Teixidò, V ............................................................................................. 19

A New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean:

King Edward Point, South Georgia Island. Norman Teferle, Addisu Hunegnaw, Philip Woodworth,

Peter Foden, Simon Williams, Jeffrey Pugh, Angela Hibbert .......................................................... 20

Mean Sea Level Observations and Processes ........................................................................................ 21


The GOCE geoid in support to sea level analysis. Thomas Gruber ................................................ 21

On the decadal trend of global mean sea level and its implication on ocean heat content change.

Lee-Lueng Fu .................................................................................................................................. 21

Deep-ocean contribution to sea level and energy budget not detectable over the past decade.

W. Llovel, J. K.Willis, F.W. Landerer, I. Fukumori ........................................................................... 22

Synchronization of sea level to oceanic and atmospheric forcing. Francisco M. Calafat.............. 22

Annual sea level variability of the coastal ocean: the Baltic Sea-North Sea transition zone.

Marcello Passaro, Paolo Cipollini, Jerome Benveniste ................................................................... 22

Global and regional sea level change over the 20th century: How can it inform us about the 21st

century? R. S. Nerem, B. D. Hamlington, F. Landerer, R. Leben, J. Willis, G. Blewitt, W. Hammond

....................................................................................................................................................... 23

A probabilistic reassessment of 20th century global mean sea level. Carling Hay, Eric Morrow,

Robert E. Kopp, Jerry X. Mitrovica .................................................................................................. 23

Considerations for estimating the 20th century trend in global Mean Sea Level. Philip R.

Thompson, Benjamin D. Hamlington ............................................................................................. 24

Sea level reconstruction from satellite altimetry and tide gauges using advanced signal

decomposition techniques. Sandra-Esther Brunnabend, Jürgen Kusche, Roelof Rietbroek, and

Ehsan Forootan .............................................................................................................................. 24

Comparing coastal and open ocean sea level variability and trend from altimetric data. A. Melet,

M. Nonti, B. Chide, B. Meyssignac, F. Birol .................................................................................... 25



Detection and attribution of global mean thermosteric sea level change. Aimée B. A. Slangen,

John A. Church, Xuebin Zhang, Didier Monselesan ........................................................................ 25

Detecting anthropogenic footprints in sea level rise. Sönke Dangendorf, Marta Marcos, Alfred

Müller, Eduardo Zorita, Jürgen Jensen ........................................................................................... 26

Posters ............................................................................................................................................... 26

Regional Sea Level change in the North Sea since 1900. Frauke Albrecht, Saskia Esselborn, Ralf

Weisse ............................................................................................................................................ 26

Sea level trends and long-term variability in the South China Sea. A.M. Amiruddin, I.D. Haigh,

M.N. Tsimplis, F.M. Calafat and S. Dangendorf ............................................................................. 27

Altimetric sea level variation and reconstruction in the Arctic. Ole B. Andersen, P. Limkilde

Svendsen, A. Aasbjerg and P. Knudsen .......................................................................................... 27

On the causes of the differential mean sea level variations between the northern and southern

hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García .................. 28

Quality control and validation of the new IOP and GOP ocean products from CryoSat-2.

Francisco M. Calafat, Paolo Cipollini, Helen Snaith, Jérôme Bouffard, Pierre Féménias, Tommaso

Parrinello ........................................................................................................................................ 28

Coastal sea level measurements and trends from improved satellite altimetry. Paolo Cipollini,

Francisco M. Calafat, David Cotton, Marcello Passaro, Helen Snaith ........................................... 29

Sea level budget over 2005 - 2013 : Missing contributions and data uncertainties. Dieng H.B.,

Cazenave A., von Schuckmann K., Ablain M., Meyssignac B. ........................................................ 30

Estimate of land water storage changes over 2003-2013 from a global water mass budget

approach. H.B. Dieng, A. Cazenave, Y. Wada, E. Schrama, S. Seneviratne, B. Meyssignac ........... 30

Impact of large-scale climate patterns on sea-level variability in the Gulf of Guinea with focus on

Ghana. Evadzi, P., Hünicke, B., Zorita, E. ........................................................................................ 31

Variation of sea level and net water flux in the Mediterranean Sea. Luciana Fenoglio-Marc ...... 31

Time-varying trends in regional sea level from tide gauge data. Thomas Frederikse, Riccardo

Riva, Cornelis Slobbe, Taco Broerse, Martin Verlaan ..................................................................... 31

Scientific roadmap towards height system unification with GOCE. Th. Gruber, R. Rummel, M.

Sideris, E. Rangelova, P. Woodworth, C. Hughes, J. Ihde, G. Liebsch, A. Rülke, Ch. Gerlach, R.

Haagmans ...................................................................................................................................... 32

The Various of Wet Tropospheric Corrections effect on the Regional Sea Level Variability in the

Indonesia Seas. Eko Yuli Handoko, Maria Joana Fernandes, Clara Lazaro .................................... 32

Ocean Bottom Pressure Records at the Permanent Service for Mean Sea Level. Angela Hibbert,

Andrew Matthews, Chris W. Hughes, Mark E. Tamisiea ............................................................... 33

The Semiannual Oscillation of Southern Ocean Sea Level. Angela Hibbert, Harry Leach, Phil

Woodworth .................................................................................................................................... 33

Celebrating 30 Years of the South Atlantic Tide Gauge Network. Angela Hibbert, Pete Foden, Jeff

Pugh, Geoff Hargreaves, Steve Mack, Phil Woodworth................................................................. 34



Observed changes and variability of mean sea-level in the Baltic Sea region during the last 200

years –a review. Birgit Hünicke,l Eduardo Zorita ........................................................................... 34

Variability of decadal sea-level trends in the Baltic Sea. Sitar Karabil, Eduardo Zorita, Birgit

Huenicke ......................................................................................................................................... 35

Forcing of Global Mean Sea Level Interannual variability for the period 1950-2010. Gabriel

Jordà, Francisco Mir Calafat, Mikis Tsimplis .................................................................................. 35

Nordic Sea Level – Analysis of PSMSL RLR Tide Gauge data. Per Knudsen, Ole Andersen, Carlo

Sørensen ......................................................................................................................................... 35

Variability of the ocean bottom pressure along the Gulf of Cadiz and its effect on the sea level

spatial distribution. Irene Laiz, Marta Marcos, Jesús Gómez-Enri, Evan Mason, Begoña Tejedor,

Alazne Aboitiz, Pilar Villares ........................................................................................................... 36

Satellite altimetry Calibration/Validation at the Australian Bass Strait site in the context of the

new missions Jason-3 and Sentinel-3. Legresy B., C. Watson, J. Church, N. White, J. Beardsley, J.

Andrewartha .................................................................................................................................. 36

Sensitivity of sea-level rise reconstruction from 1900 to present. Legresy B. , J. Church , N. White,

D. Monselesan and A. Slangen ....................................................................................................... 37

Relative sea-level change along the Italian coast during the late Holocene and projections for

2100: Coastal plain impacts based on high-resolution DTMs and geodetic data. Valeria Lo Presti.,

Fabrizio Antonioli , Alessandro Amorosi , Marco Anzidei , Gianni De Falco , Alessandro Fontana ,

Giuseppe Fontolan , Giuseppe Mastronuzzi , Enrico Serpelloni , Antonio Vecchio ........................ 37

Sea Level Oscillations in The Baltic Sea: From Minutes to Centuries. Igor P. Medvedev, Alexander

B. Rabinovich, Evgueni A. Kulikov .................................................................................................. 37

Tides in the Baltic, Black and Caspian Seas. Igor P. Medvedev, Alexander B. Rabinovich, Evgueni

A. Kulikov ........................................................................................................................................ 38

The Annual Global-Mean Thermosteric Height Budget. Christopher G. Piecuch, Rui M. Ponte .... 38

Deriving sea level from tide gauges. Jens Schröter, Manfred Wenzel, Klaus Grosfeld, Roelof

Rietbroek ........................................................................................................................................ 39

The South Atlantic sea level variability. Raisa de Siqueira Alves, Angela Hibbert and Harry Leach

....................................................................................................................................................... 39

Closing the gap between regional and global sea level in the Bay of Bengal. Bernd Uebbing,

Roelof Rietbroek, Sandra-Esther Brunnabend, Jürgen Kusche ....................................................... 40

How long does it take to measure a trend in ocean bottom pressure?. Joanne Williams, Chris

Hughes, Mark Tamisiea ................................................................................................................. 40

Modelling Sea Level Changes ................................................................................................................. 40


Long-Term Internal Variability Effects on Centennial Dynamic Sea Level Projections. Mohammad

H. Bordbar Thomas Martin, Mojib Latif, Wonsun Park.................................................................. 41

Interannual Predictability of North Atlantic Sea Level Dynamics. Robert Fraser, Laure Zanna,

Chris Wilson .................................................................................................................................... 41



Seasonal coastal sea-level prediction using a dynamical model. John A. Church, Peter C.

McIntosh, Elaine R. Miles, Ken Ridgway, Claire M. Spillman ......................................................... 41

Regional Budgets of Sea Level in the ECCO-Production Release 1 Ocean State Estimate.

Christopher G. Piecuch, Rui M. Ponte, Gael Forget, Ichiro Fukumori ............................................. 42

Imprints of oceanic intrinsic variability on altimetric measurements: an OGCM study. Guillaume

Sérazin, Thierry Penduff, Laurent Terray, Bernard Barnier, Jean-Marc Molines ........................... 42

A near-uniform fluctuation dominating sea level and ocean bottom pressure variations across

the Arctic Ocean and the Nordic Seas. Ichiro Fukumori, Ou Wang, William Llovel, Ian Fenty, Gael

Forget ............................................................................................................................................. 43

Pacific sea level trends: internally or externally forced? Felix Landerer ....................................... 43

Spatial scales and the detection of externally forced signals in regional sea surface height in

CMIP5 models. Kristin Richter, Ben Marzeion ............................................................................... 44

Worst-case scenarios for sea level rise from ice sheet melt. Carmen Boening, Nicole Schlegel,

Michael Schodlok, Daniel Limonadi, Eric Larour, Michael M. Watkins .......................................... 44

Asymmetry in regional sea level rise projections due to skewed ice sheet contributions. Renske

de Winter, Thomas Reerink and Roderik van de Wal..................................................................... 45

Posters ............................................................................................................................................... 45

Analysis of the regional pattern of sea level change due to ocean dynamics and density change

for 1993–2099 in observations and CMIP5 AOGCMs. Roberto A. F. Bilbao, Jonathan M. Gregory,

Nathaelle Bouttes .......................................................................................................................... 45

Global reconstructed daily storm surge levels from the 20th century reanalysis (1871-2010).

Alba Cid, Paula Camus, Sonia Castanedo, Fernando Méndez, Raúl Medina ................................. 46

Nonlinear model of the long-term sea-level fluctuations in the Caspian Sea. Anatoly V. Frolov . 46

Sea Level Complexity in Observations And Models. M. Karpytchev, M. Becker, M. Marcos, S.

Jevrejeva, S. Lennartz-Sassinek ...................................................................................................... 47

Explaining the spread of CMIP5 climate models in global-mean thermosteric sea level rise over

the 20th and 21st centuries. B. Meyssignac, A. Melet .................................................................. 47

Multi-annual predictability of regional sea level in a global climate model. C. D. Roberts, N.

Dunstone. L. Hermanson, M. Palmer, D. Smith .............................................................................. 48

Statistical modeling of Sea Level for regional semi-enclosed basins. Luca Scarascia and Piero

Lionello ........................................................................................................................................... 48

Projections of 21st Century Sea Level Changes for Norway. Matthew J. R. Simpson, J. Even Ø.

Nilsen, Oda Ravndal, Kristian Breili, Halfdan P. Kierulf, Holger Steffen, Eystein Jansen, Hilde

Sande, Mark Carson ....................................................................................................................... 48

Sea surface height variability in the North East Atlantic from satellite altimetry. Paul Sterlini,

Hylke de Vries and Caroline Katsman ............................................................................................ 49

What is the most robust time series analysis tool to isolate mean sea level from tide gauge

records?. Phil Watson .................................................................................................................... 49



Regional evaluation of surface mass balance forcing of an ice flow model for the Greenland Ice

Sheet using GRACE mascon solutions. D. N. Wiese, N.-J. Schlegel, M. M. Watkins, E. Y. Larour, J.

E. Box, X. Fettweis, M. R. van den Broeke ...................................................................................... 50

A review of trend models applied to sea level data with reference to the “acceleration-

deceleration debate“. H. Visser, S. Dangendorf, A.C. Petersen ..................................................... 50

Sea Level Extremes ................................................................................................................................ 51


Nineteenth Century Sea-level and Extremes on the US East and West Coast. Stefan Talke, David

Jay, Patrick Lau, Conrad Hilley, Lumas Helaire, Drew Mahedy, Ramin Familkhalili ...................... 51

Storm surge clustering and spatial footprints: How extreme was the 2013-2014 UK storm surge

season? Ivan D. Haigh, Matthew P. Wadey, Shari L. Gallop, Robert J. Nicholls ............................ 52

Regional climate variability in extreme sea levels from satellite altimetry observations over two

decades. Melisa Menendez, Philip L. Woodworth ......................................................................... 52

Time varying trends in sea level extremes. Marta Marcos, Francisco M. Calafat, Angel Berihuete,

Sönke Dangendorf .......................................................................................................................... 53

Cyclone Xaver seen by Geodetic Observations. Leonor Mendoza, Luciana Fenoglio-Marc, Remko

Scharroo, Alessandro Annunziato, Matthias Becker, John Lillibridge ............................................ 53

Future storm surge levels - the example of Denmark. Kristine S. Madsen, Torben Schmith, Tian

Tian ................................................................................................................................................ 54

Meteorological Tsunamis In The World Oceans: An Overview. Alexander Rabinovich ................. 54

The impact of sea level rise on storm surge water levels and wind waves. Arne Arns, Jürgen

Jensen ............................................................................................................................................. 55

Atmospheric Circulation Changes and their Impact on Extreme Sea Levels and Coastal Currents

in Australia. Kathleen L. McInnes, Frank Colberg, Julian O’Grady ................................................. 55

Global Secular Changes in different Tidal High Water, Low Water and Range levels. Robert J.

Mawdsley, Ivan D. Haigh,N.C. Wells ............................................................................................. 56

Posters ............................................................................................................................................... 56

How to interpret expert judgment assessments of 21st century sea-level rise? Hylke de Vries,

Roderik S.W. van de Wal ................................................................................................................ 56

Expected Vertical Load in coastal GPS due to a Tsunami like the 1775 Lisbon Tsunami: GPS

Tsunami Early-Warning capabilities. Leonor Mendoza .................................................................. 57

Analysis of recent high-frequency sea level events in the European Atlantic coast: impact on the

design of automatic algorithms for tsunami detection. Begoña Pérez Gómez, Marta Gómez

Lahoz, Enrique Álvarez Fanjul, Carlos González, François Schindele ............................................. 57

Estimation extreme sea levels from the combination of tides and storm surges for the coasts of

the Sea of Okhotsk. Georgy Shevchenko ....................................................................................... 58

Spatial variation in extreme water levels in the Baltic Sea – North Sea transition from tide gauge

records. Carlo Sørensen, Ole B. Andersen, Per Knudsen ................................................................ 58



The Impact of an Eroding Barrier Island on Extreme Water Levels in the Tampa Bay Area. Marius

Ulm, Arne Arns, Jürgen Jensen ....................................................................................................... 59

Coastal Impacts of Sea Level Changes ................................................................................................... 59


Evaluating uncertainties in future coastal flooding occurrence as sea-level rises. Gonéri Le

Cozannet, Jeremy Rohmer, Anny Cazenave, Déborah Idiera, Roderik Van de Wal, Renske de

Winter, Rodrigo Pedreros, Yann Balouin, Charlotte Vinchon, Carlos Oliveros ............................... 59

Effects of scale and input data on assessing the future impacts of coastal flooding. An

application of DIVA for the Emilia-Romagna coast. Claudia Wolff, Athanasios T. Vafeidis, Daniel

Lincke, Christian Marasmi, Jochen Hinkel ...................................................................................... 60

An assessment of extreme sea levels, waves and coastal flooding in the Maldives. Matthew

Wadey, Ivan Haigh, Sally Brown, Robert Nicholls .......................................................................... 60

Land subsidence and sea level rise at Lipari island (Italy): implications for flooding scenario.

Anzidei Marco, Bosman Alessandro, Carluccio Roberto, Carmisciano Cosmo, Casalbore Daniele,

Chiappini Massimo, Chiocci Francesco Latino, D’Ajello Caracciolo Francesca, Esposito Alessandra,

Fabris Massimo, Muccini Filippo, Nicolosi Iacopo, Pietrantonio Grazia, Sepe Vincenzo, Vecchio

Antonio ........................................................................................................................................... 61

Posters ............................................................................................................................................... 61

Characterization and Hybrid Downscaling of Wave Climate at a central Pacific atoll for extreme

sea level impacts assessment in Funafuti, Tuvalu. Ron Hoeke, Kathleen McInnes, Tom Durrant . 61

Simulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea level

rise effects. Sylvestre Le Roy, Rodrigo Pedreros, Camille André, François Paris, Sophie Lecacheux,

Fabien Marche, Charlotte Vinchon ................................................................................................ 62

Tidal influence on high frequency harbor oscillations in a narrow entrance bay. S. Monserrat, I.

Fine, A. Amores, M. Marcos ........................................................................................................... 63

A probability-based method to estimate sea level rise and future flooding risks on the Finnish

coast. Hilkka Pellikka, Milla M. Johansson, Ulpu Leijala, Katri Leinonen, Kimmo K. Kahma ......... 63

Combining sea state and land subsidence rates in an assessment of flooding hazards at the

Danish North Sea coast. Carlo Sørensen, Niels Broge, Per Knudsen, Ole B. Andersen .................. 64

Special session on Mediterranean sea level .......................................................................................... 64


To what extent can Mediterranean sea level evolve differently from global sea level rise?.

Gabriel Jordà, Damià Gomis, Marta Marcos ................................................................................. 64

On the connection between the sea level variability in the Mediterranean and in the Black Seas.

Denis Volkov, Felix Landerer .......................................................................................................... 65

Meteotsunamis in the Mediterranean Sea: rare but destructive extreme sea level events

occurring under specific synoptic conditions. Ivica Vilibic, Jadranka Sepic ................................... 65

Sea level at 2ka BP in the Balearic Islands from Roman age coastal quarries. Fabrizio Antonioli,

Marcus Heinrich Hermanns, Marco Anzidei ................................................................................... 66



Evolution of sea level and other variables on the XXI century: a picture derived from Vanimedat

II and ESCENARIOS projects. Enrique Álvarez Fanjul, Damià Gomis, E. Rodríguez-Camino, Marta

Marcos, Gabriel Jordà, R. Aznar, J. C. Sánchez-Perrino, A. Martínez Asensio, J. Llasses, Elena

Padorno, Begoña Pérez, M. N. Tsimplis, F.M. Calafat, Samuel Somot, F. Sevault, F. Adloff, J. M.

Rodríguez ....................................................................................................................................... 66

Future evolution of sea level extremes along the Mediterranean coastline as produced by the

superposition of storminess and sea level rise. Piero Lionello, Dario Conte, Luigi Marzo, Luca

Scarascia ........................................................................................................................................ 67

Posters ............................................................................................................................................... 67

On the representation of Mediterranean sea level in regional climate models. Fanny Adloff,

Gabriel Jordà, Samuel Somot, Florence Sevault, Benoît Meyssignac, Thomas Arzouse, Laurent Li,

Serge Planton ................................................................................................................................. 67

Sensitivity of the Mediterranean sea level to atmospheric pressure and free surface elevation

numerical formulation in NEMO. Antonio Bonaduce, Paolo Oddo, Nadia Pinardi, Antonio

Guarnieri ........................................................................................................................................ 68

Rescuing historic Maltese tide gauge data. Elizabeth Bradshaw .................................................. 68

Long-wave analysis of coastal sea-level records and implications for hazard monitoring and

assessment: an application to the Siracusa, Italy, tide-gauge station. Lidia Bressan, Stefano Tinti

....................................................................................................................................................... 69

Mesoscale eddies in the Western Mediterranean Sea. Romain Escudier, Ananda Pascual, Pierre

Brasseur, Lionel Renault ................................................................................................................. 69

Improved satellite altimeter mapped sea level anomalies in the Mediterranean Sea. Marta

Marcos, Ananda Pascual, Isabelle Pujol ......................................................................................... 70

Determination of Mean Dynamic Topography over the Mediterranean Sea from Jason-2

Altimetry Measurements and EGM2008 Data. Ali Rami, Sofiane Khelifa ..................................... 70

Interannual variability of the Surface Geostrophic Circulation of the Mediterranean Sea. M.

Sempere, S. Esselborn, I.Vigo ......................................................................................................... 71

Seasonal Cycle of Surface Geostrophic Circulation of the Mediterranean Sea. M.Sempere, I. Vigo,

M. Trottini, S. Esselborn ................................................................................................................. 71

High-frequency sea-level oscillations in the Mediterranean Sea: analysis and synoptic

preconditioning. Jadranka Sepic, Ivica Vilibic, Amaury Lafon, Loic Macheboeuf, Zvonko Ivanovic

....................................................................................................................................................... 72

Mean sea level secular trends from PSMSL RLR data: A case study for the Mediterranean basin.

Hebib Taibi , Mahdi Haddad .......................................................................................................... 72

Relative sea level trend and long term variability in the Northern Mediterranean from tide gauge

data: implications for future projections. Antonio Vecchio, Marco Anzidei .................................. 72



Keynote speakers

Sea-level changes during past centuries reconstructed from salt-marsh sediments. Prof.

Roland Gehrels, University of York, UK

In recent years a number of sea-level records have been published that use salt-marsh sediments,

and the fossils contained within, as indicators of sea-level change. High-quality sea-level

reconstructions from salt-marsh sediments have now been established for coastal sites in eastern

North America (Nova Scotia, Maine, Connecticut, New Jersey, North Carolina, Florida), Europe

(Iceland, Scotland, England, northern Spain), New Zealand and Tasmania. These proxy records are

particularly useful because they can provide high-resolution sea-level data beyond the period that is

covered by tide gauges, including the centuries immediately preceding the observational era. The

overlap with tide-gauge records provides a check on the validity of the proxy reconstructions. The

chronology of proxy records is provided by a range of radiometric dating techniques (AMS14C,

210Pb, 137Cs, 241Am) and by specific stratigraphic markers (e.g., pollen, tephra, Pb concentrations,

Pb isotopic ratios, paleomagnetism). High-precision Accelerator Mass Spectrometry (AMS) 14C

dating, in combination with bomb-spike AMS14C analyses, is used to circumvent limitations

associated with radiocarbon dating. The resolution of proxy records depends on the sedimentation

rates in the marshes and is usually on the order of one or two data points per decade.

Many salt-marsh based proxy sea-level records show a marked positive inflexion in the late 1800s or

the early 1900s. Combined with long tide-gauge records they demonstrate that in the first half of the

20th century the rate of sea-level rise started to exceed the late Holocene background value. The

magnitude of the 19th/20th inflexion is large in southern hemisphere sites compared to the North

Atlantic which could point at northern hemisphere land-based ice as an important melt source for a

global sea-level acceleration in the early 20th century. Along the North American east coast there is

some evidence for a period of accelerated sea-level rise in the late 18th century, when rates

approached those that have been observed in the 20th century. In Iceland the highest rates of sea-

level rise occurred during positive shifts of the reconstructed North Atlantic Oscillation (NOA) index.

A 19th/20th century sea-level acceleration is muted in the eastern Atlantic. Accelerations of sea-level

rise in the North Atlantic are confined to the regional scale and are possibly driven, at least in part, by

re-distribution of water masses due to changes in long-term wind patterns. Without exception all

salt-marsh proxy sea-level records show that the highest rates of sea-level rise of the last 2000 years

were achieved during the 20th century.

Considering vertical land motion in understanding sea level change. Prof. Guy

Woppelmann, University of La Rochelle, France

Vertical land motion plays an important role in understanding sea level change over multi-decadal to

century timescales. On the one hand, they need to be corrected in sea level trends recorded by tide

gauges to derive the climatic contributions to sea level. On the other hand, they need to be

considered to understand and anticipate the magnitude of future sea levels along specific coastlines.

http://www.york.ac.uk/


Palma de Mallorca, June 10-12, 2015 Indeed, vertical land motion can substantially amplify or attenuate sea level rise from the sole

climatic contributions. In any case, whether global or local, an accurate estimate of vertical land

motion appears mandatory. In this presentation, we will review how vertical land motion has been

considered in past estimates of global sea level change, how it can be determined and what are the

current limits in its accurate observation for understanding relative sea level changes at the coast.

The time-mean ocean dynamic topography: How well can we measure, model, and

understand it?. Prof. Chris W. Hughes, National Oceanography Centre, UK

The combination of altimetry with GOCE and GRACE gravimetry means we now have an accurate

global picture of the mean ocean dynamic topography. Addition of tide gauges, GNSS positioning,

and regional gravity measurements extends this knowledge to points precisely at the coast. With a

global range of about three metres, it is clearly important that we understand how this dynamic

component of sea level is maintained, if we are to have confidence in model predictions of how it

might change. In this talk, I will address the question of how well current ocean models can

reproduce the observed mean dynamic topography, and how well we understand the reasons for

those observations. While the models do a generally good job, I will argue that our understanding

remains rather patchy for the open ocean, and is still quite rudimentary for coastal sea level.

What are the challenges facing quantifying impacts and adapting to global sea-level

rise?. Dr. Sally Brown, University of Southampton, UK

Sea-level rise and extreme events pose on-going and long-term threats to coastlines, particularly

where hazards coincide with human population. Globally, up to 5% of the population could be

affected annually by sea-level rise by 2100 if protection standards are not raised. Such a situation in

unlikely as often humans and natural environments are responsive to change, whether due to a

sudden event, or resulting from slow incremental changes. This represents challenges: Firstly, with

much uncertainty in the projections of sea-level rise and other drivers, what levels will humans or the

natural environment be adapting to? Secondly, given a response to reduce impacts, what will be

affected and where will impacts occur? Thirdly, how will that adaptation take place?

To answer these questions, this presentation explores how past sea-levels, vertical land movements,

present observations, plus extreme events influence future projections of impacts and adaptive

responses. Sea-level rise projections and impacts today will be analysed from global to local scales,

including areas that are particularly at risk world-wide. Adaptation to reduce impacts will also be

considered, from successful past adaptation where transitions to safer coasts have been made, to

potential future responses.

Increasingly the assessment of impacts requires a systems approach, understanding multiple drivers

of coastal changes. Recognition into multiple drivers of change, their interactions and relative

importance is increasingly, such as how population and economic growth can influence or induce

impacts. Gathering accurate data on coastal change and impacts is sometimes challenging today, not

alone for the future. The adaptation challenge remains in enabling long-term climate change


Palma de Mallorca, June 10-12, 2015 adaptation today, without compromising short-term needs, development and livelihoods. Thus,

whilst sea-level rise is an important driver of change, it is increasingly recognised that other drivers

can be more responsible for adverse impacts of change: Sea-level rise remains a societal challenge,

depending on good governance to identify, monitor and reduce impacts.

Semi-empirical modelling of sea-level change. Prof. Stefan Rahmstorf, Postdam

University, Germany

The talk will discuss the semi-empirical approach to modelling sea level, its robustness and validation

issues, and the role that paleo-climatic data can play in constraining the parameters for future sea-

level rise.

References:

Rahmstorf, S. (2007), A semi-empirical approach to projecting future sea-level rise, Science,

315(5810), 368-370, doi:10.1126/science.1135456.

Vermeer, M., and S. Rahmstorf (2009), Global sea level linked to global temperature, Proceedings of

the National Academy of Sciences of the United States of America, 106(51), 21527-21532,

doi:10.1073/pnas.0907765106.

Kemp, A. C., B. P. Horton, J. P. Donnelly, M. E. Mann, M. Vermeer, and S. Rahmstorf (2011), Climate

related sea-level variations over the past two millennia, Proceedings of the National Academy of

Sciences of the United States of America, 108(27), 11017-11022, doi:10.1073/pnas.1015619108.

Rahmstorf, S., M. Perrette, and M. Vermeer (2012), Testing the robustness of semi-empirical sea

level projections, Clim. Dyn., 39(3-4), 861-875, doi:10.1007/s00382-011-1226-7.

Schaeffer, M., W. Hare, S. Rahmstorf, and M. Vermeer (2012), Long-term sea-level rise implied by 1.5

degrees C and 2 degrees C warming levels, Nature Clim. Change, 2(12), 867-870,

doi:10.1038/nclimate1584.

Bittermann, K., S. Rahmstorf, M. Perrette, and M. Vermeer (2013), Predictability of twentieth century

sea-level rise from past data, Environmental Research Letters, 8(1), doi:10.1088/1748-

9326/8/1/014013.

Sea level variability: from surface gravity waves to mean sea level. Prof. Charitha

Pattiaratchi, University of Western Australia, Australia

Coastal sea level variability occurs over a range timescales ranging from seconds to centuries.

The action of the wind on the sea surface generates surface gravity waves with periods of the order

of 10s and plays a major role in defining coastal processes. Infra-gravity waves with periods 30-300 s

influence oscillations in semi-enclosed basins such as ports and harbours. Globally, the astronomical

forces of the Sun and the Moon result in tidal variability with periods of 12 and 24 hours as well as

tidal modulations with periods up to 18.6 years. In many regions, the effects of the tides dominate


Palma de Mallorca, June 10-12, 2015 the water level variability – however, in regions where the tidal effects are small other processes also

become important in determining the local water level. In this presentation, sea level data from

Fremantle (tidal range ~0.5m), which has one of the longest time series records in the southern

hemisphere, and other sea level recoding stations from Western Australia are presented to highlight

the different processes ranging from seiches, tsunamis (generated through earthquake and

meteorological events), tides, storm surges, continental shelf waves and annual and inter-annual

variability. As the contribution from each of these processes is of the same order of magnitude – the

study of sea level variability in the region is very interesting and reveals both local and remote

forcing.

Modelling historical and future mean sea level change. Prof. Jonathan Gregory,

University of Reading, UK

The rate of global mean sea level rise (GMSLR) has accelerated during the last two centuries, from

the order of magnitude of 0.1 mm yr-1 during the late Holocene, to about 1.5 mm yr-1 for 1901-

1990, with ocean thermal expansion and glacier mass loss being probably the dominant contributors.

Process-based models suggest that the larger rate of rise since 1990, of about 3 mm yr-1, results

from increased radiative forcing of global climate change, and from increased ice-sheet outflow

induced by warming of the immediately adjacent oceans. Ocean thermal expansion is the largest

contributor to projections of GMSLR during the 21st century. For a given scenario, there is a

substantial spread in climate model projections of global ocean heat uptake and thermal expansion,

and in the geographical pattern of sea level change due to ocean density and circulation change.

Larger uncertainty in projections of GMSLR comes from the land-ice contributions, especially ice-

sheet dynamical change. These contributions also influence regional sea-level change, through their

effect on gravity and the solid Earth. By 2100 the rate of GMSLR for a scenario of high emissions

could approach the average rates that occurred during the last deglaciation, whereas for a strong

emissions mitigation scenario it could stabilise at rates similar to those of the early 21st century. In

either case, GMSLR will continue for many subsequent centuries, because of the long timescales of

ice-sheet change and deep-ocean warming, and could be partly irreversible.

Status and challenges on sea level monitoring and forecasting in the Mediterranean Dr.

Begoña Pérez Gómez, Puertos del Estado, Spain

After a review of the main characteristics of the relevant sea level processes and variability expected

in the Mediterranean sea, a detailed analysis of the adequacy of the existing monitoring networks

and forecasting systems in the region is presented. The tide gauges spatial distribution and their data

sampling and latency will be first considered, in order to determine the capability of the existing in-

situ network to fulfill the new requirements not only of climate scientists and oceanographers but

also of the sea level related hazards warning systems. The latter include both storm surge and

tsunami warning. For years storm surge forecasts have not been a priority in the Mediterranean;

however, a new set of forecasting systems are in operation nowadays, what reveals the interest of

this variable, reinforced by the expected increase of mean sea level for the next decades. Operational


Palma de Mallorca, June 10-12, 2015 general circulation models are now being designed for including sea level forecasts for this reason.

On the other hand, the risk of tsunamis in the Mediterranean is significantly larger than in the rest of

Europe: having access to high-frequency sea level data in real time from the entire basin is crucial for

an early detection and final early warning to the population: in this aspect the lack of stations from

the North of Africa is a great weakness of the regional tsunami warning systems.



Paleo Sea Level

Oral Presentations

Holocene relative sea level changes in the Baltic Sea basin: syntheses of geological and

archaeological data. Alar Rosentau In the early phases of cultural development, Mesolithic and Neolithic human populations in the Baltic

region experienced periods of significant marine transgressions and regressions owing to the melting

of the continental ice sheet and glacial isostatic land uplift. Geological–archaeological studies in the

southern Baltic Sea area have revealed a number of Mesolithic and Neolithic traces of human

occupation off the Danish and German coasts as a result of Holocene sea-level rise. Prehistoric

coastal sites in the northern Baltic Sea areas have, however, been uplifted and are located

successively at different altitudes as a result of glacial rebound. In transitional areas, prehistoric man

experienced transgressions and regressions of the shifting coastline owing to competition between

glacial rebound and eustatic sea level rise. In the current paper case studies form the transitional

area will be presented demonstrating the potential of archaeological records for reconstruction of

transgressions and regressions during the Litorina Sea. Geological and archaeological data indicate

acceleration in sea-level rise rates around 7.8 and 7.6 cal. ka BP when relative sea-level rose c. 6 m

within c. 500 years. This caused the flooding of peat and palaeosoil layers, by the submergence of the

Mesolithic sites and by the abrupt appearance of brackish water diatoms in different small lake

basins. The SPLASHCOS COST Action TD0902 completed in 2013 is producing an Atlas of over 2500

submerged prehistoric sites that may be useful in palaeo-sea level reconstructions.

Sea-level highstands in Mallorca during the last interglacial. Thomas Lorscheid, Paolo Stocchi,

Alessio Rovere, Lluís Gómez-Pujol, Bas de Boer, Thomas Mann, Hildegard Westphal, Joan J.

Fornós Deposits of the last interglacial, analysed in light of glacio-hydro-isostatic adjustment models, can provide us with information on the sea-level history and the response of polar ice-sheets in slightly warmer climates. Mallorca is one of the key areas in the Western Mediterranean for such deposits. The outcrops representing this period were intensely investigated by several authors since CUERDA 1979. According to their observations, the sedimentological and fossil content is well known and the age was determined by the presence of the Senegalese fauna and, more recently, by dating with U/Th and AAR. Three aspects of Mallorcan deposits were still underinvestigated. i) precise elevation measurements with differential GPS. ii) estimates of reference water level and indicative range of the deposits and landforms at each site. iii) estimates of glacial isostatic adjustment (GIA) effects since MIS 5e. In this study we present the results of two field trips aimed at measuring last interglacial deposits in Mallorca with high-accuracy GPS and establishing, using modern shorelines as analogs, indicative ranges and reference water level values for paleo deposits. We then used an earth-ice coupled GIA-model to investigate isostatic adjustment since MIS 5e in the island, and compared the elevation of our deposits to the expected GIA signal in this region. We discuss our results in terms of tectonics and eustasy.



Late Holocene sea-level change in the Falkland Islands: testing the Greenland melt hypothesis.

Newton, T. L., Gehrels, W. R., Daley, T.J., Blake, W. Instrumental and proxy sea-level records indicate that 20th century sea-level rise (SLR) in the North

Atlantic Ocean departed significantly from average late Holocene trends reconstructed by geological

methods. Southern hemisphere instrumental records are too short to identify any recent

acceleration. Recent studies have documented the inflexion in proxy records from New Zealand and

Tasmania, giving rise to the hypothesis that the 20th century sea-level acceleration was global in

extent. Importantly, the magnitude of change in the rate SLR at the beginning of the 20th century is

greater in southern hemisphere sites than in the North Atlantic. Such spatial differences are

potentially highly significant as sea-level theory predicts that land-based ice melt produces increased

rates of SLR in the far-field locations from which the melt source is located. The greatest rates of SLR

as a consequence of Greenland melt are predicted to be in the South Atlantic Ocean, in the seas

surrounding the Falkland Islands.

To test this hypothesis we present a new late Holocene relative sea-level (RSL) record for the

Falkland Islands, the first for this region. Our reconstruction is based on palaeo-sea level positions

derived from diatom, testate amoebae and foraminifera analyses obtained from saltmarsh

sediments. The reconstruction shows that RSL in the Falkland Islands for much of the last 7000 years

was within 0.7m of present RSL. Our high-resolution reconstruction for the last ~2000 years

documents a rising trend in RSL with a recent inflexion toward present sea level for the most recent

part of the record. This pattern of sea-level change is consistent with proxy records from Tasmania

and New Zealand which suggest that northern hemisphere land-based ice was the most significant

melt source for late Holocene global sea-level rise.

Posters

Decoding sea level changes during the MIS 5 by means of Phreatic Overgrowths on

Speleothems (POS) research in coastal caves of Mallorca (western Mediterranean). Joan J.

Fornós, Àngel Ginés, Joaquín Ginés, Francesc Gràcia, Yemane Asmeron, Bogdan P. Onac, Victor

Polyak, Paola Tuccimei The littoral caves of southeastern Mallorca have formed by the mixing of freshwater and seawater in the coastal phreatic zone, and are extensively decorated with speleothems that formed during Quaternary times when the caves become air-filled chambers. Throughout the Middle and Upper Pleistocene the caves were repeatedly flooded by glacio-eustatic sea level oscillations. The water level of each flooding event was recorded by a distinct encrustation (a Phreatic Overgrowth on Speleothems, POS) of calcite or aragonite deposited less than 40 cm below the brackish water/air interface (water table) at elevations equivalent to sea-level, over existing speleothems and along cave walls. These carbonate precipitates, which appear as horizontal alignments of crystallizations delimiting the tidal fluctuation range of the coastal water-table, are excellent recorders of sea level changes, being readily datable by U-series methods. Thus, stable sea-level stands result in POS that have grown large enough to be used as accurate sea-level markers. Marine isotope stage (MIS) 5 of the last interglacial (LIG) is of great interest because it serves as an analog for the Holocene. Changes in sea-level are, in part, indicative of the global-scale changes in climate.


Palma de Mallorca, June 10-12, 2015 Acknowledgements: This research has been supported by the MINECO projects CGL 2010-18616 and CGL-2013-48441-P to JJF and by a NSF grant AGS 1103108 to BPO and VJP

Fossil corals and speleothems as markers of past sea levels: towards a consistent global

respository. F. D. Hibbert, E.J. Rohling, P.M. Chutcharavan, A.Dutton, F. Williams Coral benchmarks and speleothem records are valuable markers of past sea level that can be dated with high analytical precision using U-Th geochronology. Corals provide a minimum estimate for the position of past sea level because they must remain submerged during growth, whereas speleothems provide upper limits for sea level because they only grow when caves are subaerially exposed. In this way, these two archives provide complementary information to bracket past sea level. Despite the fact that corals and speleothems remain a preeminent method for reconstruction and evaluating former sea levels during the Late Quaternary, there are considerable challenges in interpreting such data and in comparing data between individual studies and sites. These challenges include difficulty in constraining paleodepth of fossil corals that are also affected by taphonomy and limited context of heterogeneous reef structure for specimens collected from limited 2-D (section) or 1-D (drill-core) perspectives, diagenesis and open system behaviour of U and Th isotopes in coralline aragonite, local tectonic and isostatic influences, as well as inconsistencies and gaps in data reporting. As a first step towards tackling these heterogeneous issues, we provide an internally consistent database of published coral and speleothems U-Th data that have been used in sea level studies along with a database of modern coral depth distributions. We present an internally consistent global compilation of coral benchmarks (building on the compilations of Medina-Elizalde, 2012 and Dutton and Lambeck, 2012) containing >100 studies. We include a rigorous consideration of each error term associated with these records, such as: age, depth habitat, elevation measurement, and uplift correction. We apply commonly employed age screening methods (δ234Uinitial and detrital 232Th concentrations). We also present a new compilation of speleothem sea level markers (both U-series and radiocarbon dated). This presentation will show both datasets as currently compiled (>3,000 datapoints), and initial evaluations on a site-specific basis.

Vertical Land Movements

Oral Presentations

Combination Results of the Tide Gauge Benchmark Monitoring (TIGA) Analysis Centre Re-

processing Products. Addisu Hunegnaw, Norman Teferle In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working

Group (WG) started their re-processing campaign, which proposes to re-analyze all relevant Global

Positioning System (GPS) observations from 1994 to 2013. This re-processed data set will provide

high-quality estimates of vertical land movements for more than 400 stations, enabling regional and

global high-precision geophysical/geodetic studies. Several of the TIGA Analysis Centres (TACs) have

completed processing the full history of GPS observations recorded by the IGS global network and

many other GPS stations at or close to tide gauges, which are available from the TIGA data centre at

the University of La Rochelle (www.sonel.org). Following the recent improvements in processing


Palma de Mallorca, June 10-12, 2015 models and strategies, this is the first complete re-processing attempt by the TIGA WG to provide

homogeneous position time series.

In this study we report on a first multi-year weekly combined solution from the TIGA Combination

Centre (TCC) at the University of Luxembourg (UL). Using two independent combination software

packages, CATREF and GLOBK, we have computed a first solution of the TAC solutions already

available. These combinations allow an evaluation of any effects from the combination software and

of the individual TAC parameters and their influences on the combined solution. Some major results

of the UL TIGA multi-year combinations in terms of geocentric sea level changes will be presented

and discussed.

Models of land uplift in northern Europe. Holger Steffen Glacial isostatic adjustment (GIA) is the dominating process in northern Europe leading to a

maximum absolute land uplift of about 1 cm/year near the Swedish city of Umeå. In contrast, the

areas of the southern Baltic and North seas are subsiding due to the collapse of the peripheral bulge.

Both effects have enormous impact on coastal changes and thus on society and economy, especially

in view of current sea-level rise which may increase or decrease uplift or subsidence depending on

the location.

The Nordic countries have developed and are frequently updating land uplift models for usage in the

national geodetic surveys. We present current models that are used as well as further efforts for the

development of high precision and high resolution land uplift and GIA models which could also help

in sea level research. This includes most recent results of land uplift/subsidence and sea-level change

for the North and Baltic seas.

Relative sea level history during the Holocene and models of the glacial isostatic adjustment

process: constraints from the regions of forebulge collapse. Keven Roy, W.R. Peltier Models of the glacial isostatic adjustment (GIA) process enable us to study and understand the

regular cycles of glaciation and deglaciation that have characterized the Earth's climate over the past

800,000 years or so, in particular in terms of the large variations in sea level that have accompanied

them.

These models, which require as fundamental inputs a history of ice-sheet loading and a

representation of the radial variation of mantle viscosity, can be tested and refined by comparing

their predictions to a wide range of geophysical and geological observables, among which inferences

of past relative sea level based upon appropriate geological indicators are particularly important.

These geophysical observables, depending on the region from which they originate, provide

constraints on different features of the GIA process. However, while the relaxation process in regions

near former centers of glaciation can be parametrized in a simple fashion, its evolution in regions of

forebulge collapse, located at the periphery of the former ice sheets, is much more complex.

In this paper, we examine how recently available high-quality geological data sets of relative sea level

history for regions of forebulge collapse, such as that of Engelhart et al. (2011, Geology) for the U.S.

East coast or Engelhart et al. (2015, QSR) for the U.S. West coast, enable us to gain critical

information concerning the response of these regions and provide new complementary constraints


Palma de Mallorca, June 10-12, 2015 on GIA models and, consequently, on our understanding of relative sea level evolution around the

world. In particular, we will focus on how misfits between these new sea level evolution inferences

and current state-of-the-art GIA model predictions (ICE-6G_C (VM5a) (Peltier et al., 2015, JGR)) can

be eliminated, and then explore the consequences of these changes on our knowledge of the

deglaciation history over North America.

Posters

Updated GPS vertical velocity field at tide gauges: application to global and regional sea level

change. Médéric Gravelle, Alvaro Santamaria-Gomez, Marta Marcos, Phil Thompson, Guy

Wöppelmann The relative importance of the non-climate contribution of vertical land movement to the observed

rates of sea level change at the coast is investigated based on the last GPS solution of the ULR

consortium taking part to the International GNSS Service (IGS) Repro2 campaign. This solution stems

from 20 years of GPS data (1995-2014) reanalyzed using state-of-the-art models and corrections. It

includes 749 GPS stations distributed worldwide of which 575 are dedicated to a sea level

application. In this study, we correct the tide gauge trends for vertical land movements using the GPS

velocity field, and we investigate global and regional mean sea level estimates

Using InSAR to monitor vertical ground motions in coastal cities. G. Le Cozannet, D. Raucoules,

G. Wöppelmann Before the altimetry era, tide gauge are a unique source of information to evaluate past sea-level

changes. However, they can be affected by vertical ground motions acting at different space scales.

We use synthetic aperture radar techniques to assess these ground motions and their consequences

for geodetic instruments such as Tide Gauge, GPS, Doris stations. Summarizing results obtained at

Alexandria (Egypt; Woppelmann et al., 2013), Manila (Philippines; Raucoules et al., 2013) and Dakar

(Senegal; Le Cozannet et al., subm.), we identify different situations in terms of data availability and

ground motion context:

- when strong ground motions affect the tide gauge, the technique can easily help rejecting

tide gauges records from the database of reliable datasets (case of Manila)

- however, when no ground motions can be observed using InSAR in the vicinity of geodetic

instruments (Case of Alexandria and Dakar), it remains challenging to reach the accuracy required to

confirm that tide gauge records are indeed suitable for monitoring sea level changes.

To reach the required accuracy of this InSAR application, a large set of SAR data must have been

acquired over the area. For future science application of Sentinel 1 in the field of geodesy

underpinning sea level science, it will be necessary to define appropriate background missions

covering coastal sites where key records have been aquired.



GNSS reflectometry for tide gauge levelling. Alvaro Santamaría-Gómez, Christopher Watson,

Médéric Gravelle, Matt King, Guy Wöppelmann The GNSS reflectometry (GNSS-R) technique provides valuable information related to the geometry

and physical properties of reflecting surfaces surrounding the GNSS antenna (e.g., Global Positioning

System, GPS), including the vertical distance to them.

Here, we use sea-surface reflections of GNSS signals, recorded as oscillations in the observed signal-

to-noise ratio (SNR), to estimate the GNSS to tide gauge (TG) levelling connection and thus the

ellipsoidal height of the TG. This can be done remotely, continuously and at no additional cost.

The same technique can be used to monitor sea-surface height changes, transforming the GNSS

station in an alternative TG and thus providing sea-level change in a global height system.

We describe how this technique works, its benefits and limitations, including ongoing work and

future improvements. At the time of writing, comparison with traditional in situ levelling reveals

promising differences at the centimetre level. These differences include errors from this technique,

but also errors related to the traditional in situ levelling (errors in the GNSS antenna calibration) and

to the calibration of the TG zero. The latter opens the possibility of using this technique to monitor

the stability of the TG zero

Leveling for the altimetric control of tide gauge sensors and GNSS permanent stations in

Barcelona’s and Ibiza’s ports. Tapia Gómez, A; López Bravo, R; Gili Ripoll JA; Martínez Benjamín,

JJ; Pros LLavador, F; Palau Teixidò, V The main objective of the work performed is to determine altimetrics movements that may affect the

data stability, of both tide gauges and global positioning, transmitted by these two types of sensors.

We will present the work effected at the port of Barcelona that started in 2011, the year in which

settlements are detected in the area compared to 2008 data, and which have continued until today.

The area where the tide gauge of Puertos del Estado and the GNSS permanent station of the

Autoritat Portuària de Barcelona, distant about 50 meters, are located, is newly reclaimed land sea.

Plus, the GNSS station is located on the roof of the control tower of the port, a building 45 meters

high with a unique metal frame.

As well, we will present the work effected at the port of Ibiza, tide gauge of Puertos del Estado and

GNSS control station on the roof of a building about 10 meters high and distant about 80 meters.

The need for GNSS stations to have a clear horizon, forces their location to be on buildings which

difficult a precise leveling, we will describe leveling geometric designed as ad hoc.

The tasks carried out in the port of Barcelona until September 2014, settlements have been detected

up to 39 millimeters, while in the port of Ibiza the settlements are estimated at a value close to 1

mm/year.

The results confirm that altimetrics checks need to be done periodically starting from the moment

they are installed and in fixed points. The frequency of checks will be determined by the results that

are obtained.



A New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean:

King Edward Point, South Georgia Island. Norman Teferle, Addisu Hunegnaw, Philip Woodworth,

Peter Foden, Simon Williams, Jeffrey Pugh, Angela Hibbert In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed

at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried

out as part of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements

(ACCLAIM) programme. In 2013 the KEP Geodetic Observatory was established in support of various

scientific applications including the monitoring of vertical land movements at KEP. Currently, the

observatory consists of two state-of-the-art Global Navigation Satellite System (GNSS) stations with

local benchmark networks. In 2014 a tide board was added to the tide gauge, which, together with

the measurements from the KEP Geodetic Observatory, now enables a calibration of the tide gauge.

This will make it possible to include the KEP tide gauge in the Permanent Service for Mean Sea Level

(PSMSL) database and make it available for future sea level studies.

In this study, we will present the GNSS and levelling observations from the KEP Geodetic Observatory

for the period from February 2013 to May 2015 used for the calibration of the tide gauge. While it is

still too early to obtain accurate vertical land movement estimates from the GNSS data, the levelling

campaigns in 2013 and 2014 indicated 7-9 mm of subsidence near the tide gauge. For the

computation of the new height datum, geoid undulations derived from a seamless combination of

the latest Gravity Observation Combination (GOCO) and Earth Gravitational Model (EGM) 2008

models were used. The use of this combined gravity model introduced a datum shift of

approximately -24 cm compared to the previous datum.



Mean Sea Level Observations and Processes

Oral Presentations

The GOCE geoid in support to sea level analysis. Thomas Gruber The accuracy of the final geoid models derived from GOCE and complementary satellite data is

estimated to be about 1.5 cm with 100 km spatial resolution and worldwide consistency. This opens

new possibilities for sea level research, where geoid quality and consistency over large distances

often plays an important role. One example for this is the problem of connecting tide gauge records

across the oceans. In principle there are two ways to perform this connection. First, via the oceans by

estimating the dynamic ocean topography at the tide gauges from the GOCE geoid and satelllite

altimetry and, second, by unifying the regional or continental height systems to which the tide

gauges are connected by estimating their offsets to the global GOCE geoid. Both approaches in

principle require the true geoid at the tide gauge locations, which not always is provided by the

GOCE geoid because of its limited spatial resolution or in other words due to the omission error, i.e.

the part of the signal which cannot be observed with GOCE. The paper provides a summary of the

characteristics of the GOCE geoid solutions, some results for connecting tide gauges applying both

methods and specifically investigates the impact of the omission error on the results obtained.

On the decadal trend of global mean sea level and its implication on ocean heat content

change. Lee-Lueng Fu The variability of the trend of global mean sea level on decadal scales is of great importance to

determining its long-term evolution. In this paper we have reexamined the approach to estimating

such a trend. Most climate time series such as the altimeter sea level record are characterized by a

red noise process. The temporal correlation of the residuals from a linear trend fit has often been

neglected in estimating the uncertainly of the fit, leading to underestimate of its errors. We suggest

to cast the problem as optimal estimation to minimize the residuals weighted by autocovariance.

The approach takes into account the various time scales present in the time series and their effects

on estimating a trend. In the case of the altimeter record, the resulting error estimate is a factor of

four larger than estimates neglecting the temporal correlation. Although the dominant error in the

altimetric sea level trend is derived from comparison to tide gauge observations, which have long-

term (tectonic scales) errors from land motions. Such errors essentially cause a bias in the estimate

of a trend over decadal scales. Such bias would be canceled for evaluating the change of decadal

trends, of which the errors are thus dominated by the uncertainty in the estimation error. The

approach was also applied to the sea level change from ocean mass estimated from the GRACE

observations of the change of Earth’s gravity. The steric sea level was then estimated from the

difference between the sea level from altimetry and its mass component from GRACE. The decadal

trend of steric sea level was favorably compared to the Argo observations. The results have shed

light on the prospects of estimating decadal change in ocean heat content from space, a variable of

great importance to climate change and sea level rise.



Deep-ocean contribution to sea level and energy budget not detectable over the past decade.

W. Llovel, J. K.Willis, F.W. Landerer, I. Fukumori As the dominant reservoir of heat uptake in the climate system, the world’s oceans provide a critical

measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-

level rise and Earth’s energy budget between January 2005 and December 2013. Direct

measurements of ocean warming above 2,000m depth explain about 32% of the observed annual

rate of global mean sea-level rise. Over the entire water column, independent estimates of ocean

warming yield a contribution of 0.77 +/- 0.28mm/yr in sea-level rise and agree with the upper-ocean

estimate to within the estimated uncertainties. Accounting for additional possible systematic

uncertainties, the deep ocean (below 2,000 m) contributes -0.13+/-0.72mm/yr to global sea-level rise

and -0.08+/-0.43W/m^2 to Earth’s energy balance. The net warming of the ocean implies an energy

imbalance for the Earth of 0.64 +/- 0.44W/m^2 from 2005 to 2013.

Synchronization of sea level to oceanic and atmospheric forcing. Francisco M. Calafat Synchronization is a basic phenomenon in physics wherein the phases of two oscillators, either

chaotic or periodic, become entrained to a common behaviour through coupling or forcing. Strictly

speaking, the ocean-atmosphere system represents an example of bidirectional coupling in which the

two subsystems mutually influence each other's dynamics, although in many ocean applications one

can assume, without incurring significant error, that the atmosphere is a freely-evolving force acting

upon the ocean. Irrespective of the coupling configuration, the interaction between the two

subsystems can lead to the appearance of relations between some of their properties that are crucial

too understand the evolution of the ocean, especially in a situation of climate change. Here we are

concerned with the synchronization, in the sense of phase-locking, between some of the

components of sea level and their driving forces. In particular, we investigate changes in the

dynamics of the phase of sea level extremes and the seasonal sea level cycle in tide gauge

observations in relation to the evolution of their driving mechanisms such as wind forcing, surface

heat fluxes, and hurricane seasonality. In order to detect phase shifts or locking we explore

instantaneous phases via a non-linear and non-Gaussian state-space model which is learned through

a particle Markov chain Monte Carlo filter.

Annual sea level variability of the coastal ocean: the Baltic Sea-North Sea transition zone.

Marcello Passaro, Paolo Cipollini, Jerome Benveniste Up to now, the use of satellite altimetry for sea level studies in the coastal regions has been has been

limited due to the lack of confidence in the accuracy of the satellite measurements close to land and

in shallow areas. This research focuses on validating the coastal capabilities of satellite altimetry to

detect the annual cycle of sea level on a regional and sub-regional scale. The study area is the

intersection of North Sea and Baltic Sea.

Coastal-dedicated satellite altimetry data (from ALES) are compared with the state-of-the-art

standard altimetry products (from the ESA Climate Change Initiative). Estimations of the annual cycle

of sea level are also derived from a network of coastal tide gauges. The analysis spans the Envisat


Palma de Mallorca, June 10-12, 2015 years (2002-2010) and is performed both along each satellite track (or grid point for the mapped

dataset) and by dividing the area into sub-basins.

We demonstrate that dedicated processing improves the quality of the altimetry dataset in the area,

showing for example that the root mean square difference between the annual cycle sinusoid

estimated by the tide gauges and coastal altimetry within only 15 km of the coast is constantly less

than 1.5 cm. We provide interpretation of the results by using wind stress data and a local

climatology, highlighting small-scale differences, such as a smaller annual variability in the West

Arkona due to steric cycle phase opposed to mass component phase and a slope in the amplitude of

the annual cycle along the Norwegian coast due to a coastal current.

To our knowledge, this is the first time that the improvements brought by coastal satellite altimetry

to the description of the annual variability of the sea level have been evaluated and discussed. The

methodology applied in this paper is generally applicable to other coastal areas and the coastal

reprocessed ALES dataset will soon be available to the community over the whole coastal ocean.

Global and regional sea level change over the 20th century: How can it inform us about the 21st

century? R. S. Nerem, B. D. Hamlington, F. Landerer, R. Leben, J. Willis, G. Blewitt, W. Hammond Tide gauges, satellite altimetry, satellite gravity, and hydrography provide a rich set of measurements

from which to understand natural and anthropogenic sea level variations over the 20th century.

These observations can help partition the contributions from thermal expansion, the melting of ice,

changes in land water storage, and a variety of other sources, and also help understand the regional

variations from global average sea level change. However, the satellite observations only cover the

last decade or two and so understanding the long-term record of 20th century sea level change is

challenging due to the presence of decadal variability. We will review the observational record and

discuss the impacts on global and regional sea level change over the 20th century, including the

impacts of climate variability (ENSO, PDO, etc.). We will discuss the implications of the this record for

projecting future global and regional sea level change over the 21st century and what the limiting

error sources and challenges are.

A probabilistic reassessment of 20th century global mean sea level. Carling Hay, Eric Morrow,

Robert E. Kopp, Jerry X. Mitrovica Tide gauge observations of sea level over the 20th century show significant spatial and temporal

variability on a continuum of length and time scales. The variability seen in these records is due to

processes that include ongoing sea-level changes due to glacial isostatic adjustment (GIA), thermal

expansion of the ocean, dynamic effects associated with ocean circulation changes and ocean-

atmosphere interactions, and present day melting of land ice. The geographic signatures associated

with this latter process are unique for every ice sheet and glacier, and can be used, in principle, to

estimate the contribution of each source to global sea-level change. The combination of data sparsity

and geographic variability makes it challenging to obtain robust estimates of global mean sea level

(GMSL).

We overcome the difficulties associated with the tide gauge records by modeling the underlying

physics responsible for the observed geographic variability in the observations. This allows us to infer


Palma de Mallorca, June 10-12, 2015 global information from the incomplete records. Using two probabilistic techniques, we conclude

that GMSL rose at 1.2 ± 0.2 mm/yr over the time period 1901-1990, ~30-40% lower than previous

estimates. This lower rate agrees with the sum of the estimated individual GMSL contributions

recently reported in the Fifth Assessment Report of the IPCC, allowing us to close the 20th century

sea-level budget. By contrast, our estimated rate for the period 1993-2010 (3.0 ± 0.7 mm/yr) agrees

with previously published results, suggesting that the acceleration of sea-level rise over recent

decades has been significantly greater than previously thought.

Considerations for estimating the 20th century trend in global Mean Sea Level. Philip R.

Thompson, Benjamin D. Hamlington Recent reconstruction efforts result in a range of published estimates for the 20th century trend in

global mean sea level (GMSL). Discrepancies can be attributed to two factors: 1) differences in

analysis and/or reconstruction techniques; and 2) differences in tide gauge selection and quality

control of the data. In this paper, we isolate the effect of tide gauge selection on estimates of GMSL

by applying a simple and consistent analysis technique to the sets of tide gauges used in three recent

publications: Ray and Douglas (2011), Church and White (2011), and Hay et al. (2015). We describe

the differences in selection philosophy employed by each study, and we show how tide gauge

selection choices can affect estimates of the long-term global trend derived from each set. In

particular, we find that discrepancies between 20th century GMSL trend estimates are related to the

decision to include or exclude gauges from a small number of coastal regions. These regions exhibit

large-scale coherent variability and/or long-term trends that are inconsistent with changes in GMSL,

and we conclude that any reconstruction including gauges from these regions must demonstrate the

ability to account for this non-global variability using non-uniform basis functions. Finally, we

demonstrate how to treat tide gauge selection as an analytical process and examine the tide gauge

residuals from GIA and fitted non-uniform basis functions in a reconstruction. We show which tide

gauge records contain reasonable long-term trends and regional variability consistent with spatial

basis functions derived from altimetry. We also evaluate which altimetry basis functions are actually

useful when accounting for decadal and longer sea level variability in tide gauges. The balance

between including more tide gauge data vs. the limitations of the basis functions available to the

reconstruction is key to achieving optimal estimates of 20th century GMSL trends.

Sea level reconstruction from satellite altimetry and tide gauges using advanced signal

decomposition techniques. Sandra-Esther Brunnabend, Jürgen Kusche, Roelof Rietbroek, and

Ehsan Forootan Satellite altimetry and tide gauge records are used in many studies for the reconstruction of global

mean sea level and regional mean sea level. Most of them used the method of empirical orthogonal

functions (EOF) to reduce noise and investigate the different signals in climate time series. However,

EOFs have some limitations, e.g. the method falls short of isolating physical signals, limiting the

ability to separate individual modes of sea level variations. In addition, the physical interpretation of

the derived modes is limited because the EOF method assumes different modes to be orthogonal

and consequently uncorrelated, which is not necessarily true for physical signals.


Palma de Mallorca, June 10-12, 2015 Therefore, we investigate the use of more advanced signal decomposition techniques such as

Rotated EOFs (REOFs), Independent Component Analysis (ICA), and their complex extensions to

reconstruct global and regional sea level change from altimetry data. We anticipate that these

methods better characterize independent physical processes in ocean dynamics as they uses higher

than second-order moments of the probability density function derived from available sea level

records. The complex extensions provide the opportunity to deal with the non-stationary behavior of

sea level change. First results will be compared with sea level estimates derived from ocean modeling

and sea level forward modeling.

Comparing coastal and open ocean sea level variability and trend from altimetric data. A. Melet,

M. Nonti, B. Chide, B. Meyssignac, F. Birol Since 1993, altimetry has provided an unprecedented opportunity to study sea level variability with a

quasi-global coverage. Satellite altimetry indicates that sea level has been rising fast in response to

global warming, but with large regional variations. However, standard altimetric data do not allow to

study sea level variability and rise close to the coast, where the socio-economic impacts of sea level

rise are the greatest. Recently, along-track altimetric data have been reprocessed at LEGOS/CTOH

using algorithms adapted to coastal regions to recover information in coastal zones (this reprocessed

coastal product is referred to as the XTRACK dataset here).

In this study, we first intercalibrate the along-track Topex-Poséidon, Jason-1 and Jason-2 XTRACK

dataset to that distributed by AVISO to have consistent sea level data in the open ocean. Then, sea

level trends are computed with the XTRACK dataset to analyse how sea level rise varies as a function

of the distance to the coast. Spectral analyses are performed to assess the frequency bands for which

coastal sea level variability and open ocean variability differ.

Analyses are performed over two regions (West coast of Africa and southwest Pacific). They will be

extended to the global ocean to provide a map of sea level trends over the 1993-2012 period for the

coastal zones of the global ocean.

Detection and attribution of global mean thermosteric sea level change. Aimée B. A. Slangen,

John A. Church, Xuebin Zhang, Didier Monselesan Changes in sea level are driven by a range of natural and anthropogenic forcings. To better

understand the response of global mean thermosteric sea level change to these forcings, we

compare three observational data sets to experiments of 28 climate models with up to five different

forcing scenarios for 1957–2005. We use the preindustrial control runs to determine the internal

climate variability. Our analysis shows that anthropogenic greenhouse gas and aerosol forcing are

required to explain the magnitude of the observed changes, while natural forcing drives most of the

externally forced variability. The experiments that include anthropogenic and natural forcings

capture the observed increased trend toward the end of the twentieth century best. The observed

changes can be explained by scaling the natural-only experiment by 0.70 +/- 0.30 and the

anthropogenic-only experiment (including opposing forcing from greenhouse gases and aerosols) by

1.08 +/- 0.13 (+/-2𝜎).



Detecting anthropogenic footprints in sea level rise. Sönke Dangendorf, Marta Marcos, Alfred

Müller, Eduardo Zorita, Jürgen Jensen While there is scientific consensus that global mean sea level (MSL) is rising since the late 19th

century, it remains unclear how much of this rise is due to natural variability or anthropogenic

forcing. Uncovering the anthropogenic contribution requires profound knowledge about the

persistence of natural MSL variations. This is challenging, since observational time series represent

the superposition of various processes with different spectral properties. Here we statistically

estimate the upper bounds of naturally forced centennial MSL trends on the basis of two separate

components: a slowly varying volumetric (mass and density changes) and a more rapidly changing

atmospheric component. Resting on a combination of spectral analyses of tide gauge records, ocean

reanalysis data and numerical Monte-Carlo experiments, we find that in records where transient

atmospheric processes dominate, the persistence of natural volumetric changes is underestimated. If

each component is assessed separately, natural centennial trends are locally up to 0.5 mm/yr larger

than in case of an integrated assessment. This implies that external trends in regional MSL rise

related to anthropogenic forcing might be generally overestimated. By applying our approach to a

spatially homogeneous centennial ocean reanalysis (SODA) in combination with fingerprints of glacial

ice melt and hydrology changes, we estimate maximum natural trends in the order of 1 mm/yr for

the global average. This value is larger than previous estimates, but consistent with recent paleo

evidence from periods in which the anthropogenic contribution was absent. Comparing our estimate

to the available reconstructions of 20th century global MSL rise of 1.3-2.0 mm/yr suggests a

minimum external contribution of at least 0.3 mm/yr. We conclude that an accurate detection of

anthropogenic footprints in global and regional MSL rise requires a more careful assessment of the

persistence of intrinsic natural variability.

Posters

Regional Sea Level change in the North Sea since 1900. Frauke Albrecht, Saskia Esselborn, Ralf

Weisse The regional mean sea level of the North Sea is investigated. Variability in both time and space are

analysed for the period 1900-2012. The sea level is reconstructed using the approach presented in

Church et al. (2004)*. That is tide gauge and altimetry data are combined using the advantage of

each dataset. The length of the tide gauge data is combined with the spatial distribution of the

altimetry data using an EOF-analysis. The analysis considers yearly means of 14 GIA corrected tide

gauges, which are equally distributed over the region. For the altimetry data yearly means of Topex,

Jason-1 and Jason-2 data are used. The altimetry data covers the area 4°W-9°E, 51°N-60°N with a

resolution is 0.5°x 0.5°. No inverse barometer correction has been applied.

The quality of the reconstruction is validated against the altimeter data. The patterns of the spatial

variability are well reconstructed. The spatial correlation for the period 1993-2012 is in general very

good (0.6) with exceptions in the southwest and northwest, where the values are a bit lower. The

linear trend of the time period 1993-2012 shows the general pattern of the altimetry data, but an

overestimation especially in the German Bight and along the Danish coast can be seen. The spatial

mean of the reconstruction is compared to earlier reconstructions of this area. Its linear trend for the

period 1900-2012 is 1.2mm/yr. This value is a bit lower than reconstructions of the same area only


Palma de Mallorca, June 10-12, 2015 using tide gauge data, which might be due to the relatively few tide gauge data used or the reduced

variability of the time series, which is a byproduct of the method.

Additionally hindcast dataset CoastDat is included in the analysis. It contains wind and the inverse

barometric effect from 1948-2012. This data has been subtracted from the tide gauge and altimetry

data in order to analyse how much the linear trend is influenced by the meteorological signal.

*Church, J.A., White N.J., Coleman R., Lambeck K., and Mitrovica J.X. (2004) Estimates of the regional

distribution of sea-level rise over the 1950 to 2000 period, J. Clim., 17, 2609–2625.

Sea level trends and long-term variability in the South China Sea. A.M. Amiruddin, I.D. Haigh,

M.N. Tsimplis, F.M. Calafat and S. Dangendorf During the last two decades, sea level rise around the South China Sea (SCS) is nearly three times of

the global mean rate. Due to the economic importance and high density population, rising sea levels

will severely threaten this region. Here, inter-annual variability and longer-term trends in mean sea

level in the SCS have been examined using satellite altimetry data and tide gauge records, along with

steric and meteorological data. Relative sea level trends from tide gauge records longer than 40 years

range between –0.5 ± 0.2 mm/yr and 5.4 ± 0.4 mm/yr. The contribution of atmospheric pressure

changes to sea level trends at the tide gauges is statistically non-significant. For the period 1993-

2012, the basin average sea level rise obtained from altimetry data is 4.8 ± 1.2 mm/yr. The trend is

larger in the Philippines Sea with maximum values reaching 9.9 ± 2.1 mm/yr. Steric trends (1993-

2012) computed down to 1500 m depth, explains a large fraction of the observed trends in most

parts of the Philippines Sea with values as large as 7.5 ± 2.2 mm/yr. Using regional indices from the

tide gauge records, the first and second Empirical Orthogonal Function (EOF) explains 80% and 12%

of the variance, respectively. The first EOF is closely related to the El Niño Southern Oscillation

(ENSO) while the second EOF is associated with the Indian Ocean Dipole (IOD). Inter-annual sea level

variability, especially in the Philippines Sea and the Malacca Strait, can be partly explained by the

influence of ENSO. A considerable part of the variability in the Malacca Strait and off the southern

coast of Vietnam is found to be linked with the IOD. The strength of the link between inter-annual

sea level variability and these climate indices as measured by correlation varies over time. Further

research will assess the decadal variability and their forcing mechanism.

Altimetric sea level variation and reconstruction in the Arctic. Ole B. Andersen, P. Limkilde

Svendsen, A. Aasbjerg and P. Knudsen The Arctic is still extremely challenging region for the use of remote sensing for ocean studies and

particularly satellite altimetry. One is the fact that despite 20 years of altimetry only very limited sea

level observations exists in the interior of the Arctic Ocean. By carefully reprocessing and re-editing

conventional altimetry from ERS-1/ERS-2 and Envisat we have been able to derive a multi-decade

time series containing far more data in the interior of the Arctic Ocean than ever before, by

furthermore adding in 3 years of Cryosat-2 SAR data quantified as either Lead or Ocean data within

the Cryosat-2 SAR mask in the Arctic Ocean we can further extend the time series to more than 20

years. Good altimetric data is seen to crucial for sea level studies and profoundly for sea level

reconstruction where we present a 60 years sea level reconstruction based on this new data set.


Palma de Mallorca, June 10-12, 2015 We here present a new multi-decade altimetric dataset and a 60 year reconstruction of sea level

based on this together with tide gauge information. We also highlight the importance of careful

editing of tide gauges in the Arctic where many tide gauges are more representative of river

variations than actual sea level variations.

On the causes of the differential mean sea level variations between the northern and southern

hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García In the last decades, satellite altimetry has provided sea level data more densely distributed in space

and time, with the consequent improvement of information with respect to the sea level observation

series from historical tide gauge records. It is well known that sea level does not rise (or fall)

uniformly all over the oceans, but follow complex patterns in space and time. Among the attempts of

gathering the observed behaviour in few intuitive parameters, a candidate to consider are the

variations restricted to some large chosen oceanic areas. Several studies have shown, e.g. differences

in the secular trend of sea level variations between the northern and southern hemispheres of the

Earth. In 2011 Barkin pointed an averaged trend of about 2.45 ± 0.32 mm / year sea level rise in the

northern hemisphere, in contrast to a much lower average rate of 0.67 ± 0.30 mm / yr in the

southern one. That estimation showed a clear difference of 1.78 mm / year between the N/S

hemispherical rates of sea level change. It is in good agreement with more recent determinations

obtained from the coastal tide gauge observations, like those reported by Woppelman et al. in 2014,

which included corrections for the vertical geodetic displacements of the stations.

That observed behaviour has not been fully explained yet. Among the potential causes, we analyze

the effects of the changes of the gravitational attraction of the core, which is not invariant but

experiences changes of various reported origins. Among them, we consider here the shifting with

respect to the centre of mass of the whole Earth, which was suggested by Barkin et al in 2008 and

treated later in 2011. In that previous work it was shown that the displacement of the core relative

to the mantle would generate a slow tide of inner origin, asymmetric with respect to the equator and

thus redistributing the oceanic and atmospheric masses between the southern and the northern

hemispheres. This dynamical effect can contribute to driving the observed distinct behaviour of

mean sea level rates between the opposite northern and southern hemispheres and even to be a

leading mechanism to an extent that must be assessed.

Along with the fundamental core of the tide, we consider other phenomena that can produce secular

changes in sea level. Factors as e.g. the role of the asymmetric arrangement of the continents in

relation to the northern and southern hemispheres, and the ocean volume and its thermal

expansion, have been also invoked in the literature as potential sources of differences in the regional

behaviour of sea level variations.

Quality control and validation of the new IOP and GOP ocean products from CryoSat-2.

Francisco M. Calafat, Paolo Cipollini, Helen Snaith, Jérôme Bouffard, Pierre Féménias, Tommaso

Parrinello CryoSat-2 is a huge asset to the oceanographic community, and the exploitation of its data over the

ocean represents a welcome additional return for ESA’s investment in a mission whose primary

objective is to monitor the cryosphere. The CryoSat Project has approved, in the frame of the CryoSat


Palma de Mallorca, June 10-12, 2015 routine phase, the generation of additional ocean products which are available since April 2014.

These are the Interim Ocean Products (IOP), normally available within 2-3 day from acquisition, and

the Geophysical Ocean Products (GOP), with consolidated orbits and available 30 days after

acquisition. To enable their full exploitation by the scientific and operational oceanographic

communities, these new ocean products need to be thoroughly quality-controlled and validated.

Here we present the results of the scientific quality control performed at the UK National

Oceanography Centre (NOC) within the framework of the CryOcean-QCV project. The assessment

and quality control of the data is conducted both daily and monthly on a global scale for the L2 IOP

and GOP products and includes coverage/completeness, data flow and latency analysis, along-track

and crossover analysis, and estimation of error levels and measurement precision. Diagnostics are

computed for the sea surface height (SSH), significant wave height (SWH), radar backscatter

coefficient (sigma0), wind speed and mispointing parameters.

In addition we present an absolute validation of the altimetric SSH for the GOP product against sea

level observations from high-quality tide gauges equipped with Global Positioning System (GPS)

receivers. Finally, the validation is extended by comparing the SSH from CryoSat-2 with that from

other altimetric missions (e.g. Jason-2).

Coastal sea level measurements and trends from improved satellite altimetry. Paolo Cipollini,

Francisco M. Calafat, David Cotton, Marcello Passaro, Helen Snaith Satellite altimetry in the coastal zone has improved significantly in recent years, thanks to the

dedicated efforts of a large community of researchers worldwide. More and better measurements of

sea level (and significant wave height) are recovered thanks to improved waveform processing

(retracking) and corrections, as showcased at the annual workshops of the coastal altimetry

community (http://www.coastalt.eu/community). In this contribution, after a concise review of the

advances in coastal altimetry, we present results on coastal altimetry activities being carried out at

NOC.

Within the ESA Climate Change Initiative Sea Level Project we have first quantified the user

requirements in terms of accuracy and long-term stability in the coastal domain. We will present and

discuss the findings – for instance long-term stability requirements of 0.5–1.0 mm/y at regional level

and of 0.2–0.5 mm/y for a ‘global coastal’ mean linking the global estimates of sea level rise from

open-ocean altimetry with the Tide Gauges. We will also describe work on screening and filtering of

the high-rate altimetric data and the atmospheric and geophysical corrections in the coastal zone,

and the assessment of coastal retrackers showing the improvements from the sub-waveform

approach adopted in the ALES retracker (Passaro et al., Rem. Sens. Env, 2014) in comparison with a

number of well-monitored and quality-controlled tide gauges.

In a demonstration project funded by the UK Space Agency, Sea Level SpaceWatch, we have

computed the latest figures on observed sea level around the UK (rolling annual mean sea level, the

amplitude of the annual cycle and both the annual-scale trend and decadal-scale trend) from the

Envisat/AltiKa altimeter series, and compared them with selected Tide Gauges. We will show the

results of this validation and discuss the potential transition towards an operational sea level advice

service aimed at supporting long term planning and risk management.



Sea level budget over 2005 - 2013 : Missing contributions and data uncertainties. Dieng H.B.,

Cazenave A., von Schuckmann K., Ablain M., Meyssignac B. Based on the sea level budget closure approach, this study investigates the residuals between

observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass)

for the period January 2005 to December 2013. The objective is to identify the impact of errors in

one or several components of the sea level budget on the residual time series. This is a key issue if

we want to constrain missing contributions such as the contribution to sea level rise from the deep

ocean (> 2000m). For that purpose, we use several data sets as processed by different groups: six

altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric

sea level and three GRACE-based ocean mass products. We find that over the study time span, the

observed trend differences in the residuals of the sea level budget can be as large as ~0.5 mm/yr.

These trend differences essentially result from the processing of the altimetry data (e.g., choice the

geophysical corrections and method of averaging the along-track altimetry data). Such large trend

differences in the residuals may prevent from accurately constraining deep ocean steric changes. At

short time scale (from sub-seasonal to multiannual),residual anomalies are significantly correlated

with ocean mass and steric sea level anomalies (depending on the time span), indicating that the

residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric

data. Efforts are needed to reduce these various sources of errors before using the sea level budget

approach to estimate missing contributions such as the deep ocean heat content.

Estimate of land water storage changes over 2003-2013 from a global water mass budget

approach. H.B. Dieng, A. Cazenave, Y. Wada, E. Schrama, S. Seneviratne, B. Meyssignac We estimate the land water storage component over the 2003-2013 time span using a global water

mass budget approach, i.e. comparing the ocean mass change from GRACE space gravimetry to the

sum of the main water mass components of the climate system : glaciers, Greenland and Antarctica

ice sheets, atmospheric water budget and land water storage (the latter being the unknown quantity

to be estimated). Instead of considering a mean trend over the study period, we account for the

change in rates (acceleration) seen in several terms of the mass budget equation (e.g., Grace-based

ocean mass, Greenland and Antarctica mass balance). For the glaciers and ice sheets, we use

published mass balance estimates based on various types of observations covering different periods

of the 2003-2013 decade, from which we compute a changing rate through time. We also use time

series of mass balance rates (that also provide acceleration estimates). This allows us to derive a time

series of land water storage rate over the study period. The computed changing rate in global land

water storage mainly represents direct anthropogenic effects on land hydrology, i.e. the net effect of

ground water depletion and impoundment of water in man-made reservoirs (estimates from an

hydrological model shows that natural climate variability and climate change essentially cause

interannual fluctuations in the net land water storage but negligible trend). Our results are compared

with independent estimates of human-induced changes in global land hydrology.



Impact of large-scale climate patterns on sea-level variability in the Gulf of Guinea with focus on

Ghana. Evadzi, P., Hünicke, B., Zorita, E. The analysis of sea-level variability along West Africa has been hampered by the limited length and

quality of tide-gauge records. Ghana is the only country along the West African coast with relatively

long sea-level records available.

In this study we aim on characterizing the large-scale climate forcing that drive mean sea-level

variability at and off the coast of Ghana and study its decadal variability and long-term trends in the

observational period.

For this purpose, available sea-level information (referred from tide gauges, satellite altimetry,

gridded reconstructions and ocean model simulations) will be statistically analyzed together with

meteorological data from reanalysis products and climate model simulations. The main large-scale

climate factors driving regional mean sea level at these timescales will be identified and quantified.

Variation of sea level and net water flux in the Mediterranean Sea. Luciana Fenoglio-Marc The sea level, the mass-induced sea level variability and the net mass transport between

Mediterranean Sea and the Atlantic Ocean are derived in the interval 2002-2014 from tide gauges

and satellite-based observations. In the interval 1960-2014 they are obtained by combining multiple

observational datasets and results from a regional climate model simulation.

The decadal variation in mass is the main contributor to the sea level variability in the Mediterranean

Sea and appears to be related to changes in the Atlantic Ocean. The decadal variations in net

evaporation at the sea-surface, such as the increase since 1970, drive the changes in net inflow at

Gibraltar.

Compared to previous analysis, at basin scale an improved agreement between sea level observed by

altimetry and derived from the steric-corrected GRACE data is found using sea level data of the ESA

Climate Change Initiative (CCI) and release 5 of the GRACE data.

At spatial scales the improved GRACE data and filters reduce the hydrological leakage giving a better

agreement between the components.

Time-varying trends in regional sea level from tide gauge data. Thomas Frederikse, Riccardo

Riva, Cornelis Slobbe, Taco Broerse, Martin Verlaan Knowledge and understanding of contemporary changes is necessary to better predict future sea

level rise, and one of the primary observational datasets is represented by tide gauge records. We

propose a new method to estimate trends from tide gauge data by using a state space formulation,

which couples the direct observations to a predefined state space model by using a Kalman filter. The

model consists of a time-varying trend and seasonal cycle, and variability induced by several physical

processes, such as wind, atmospheric pressure changes and teleconnection patterns. This model has

two advantages over the classical least-squares method that uses regression to explain variations

due to known processes: it can account for variations in phase and amplitude of the seasonal cycle,

and it allows the trend to vary over time. This time-varying trend consists of a secular trend and low-

frequency variance that is not explained by any other term in the model. As a test case, we have used


Palma de Mallorca, June 10-12, 2015 tide gauge data from stations around the North Sea over the period 1980-2013: the time-varying

trend clearly shows a large decadal variability. To validate whether this model is correctly explaining

the observed variance, we have compared our results against time-series where the variability has

been predicted by the Dutch Continental Shelf Model (DCSM), a 2-dimensional storm surge model

that estimates the effects of wind, pressure and tides. Trends obtained from the DCSM-corrected run

show patterns at inter-annual and decadal scales that are very similar to the trends obtained with

the state space model. The mean trends over the period 1980-2013 are also very similar for both

models, but there are significant differences when these estimates are compared to results from a

classical least-squares analysis.

Scientific roadmap towards height system unification with GOCE. Th. Gruber, R. Rummel, M.

Sideris, E. Rangelova, P. Woodworth, C. Hughes, J. Ihde, G. Liebsch, A. Rülke, Ch. Gerlach, R.

Haagmans GOCE allows the determination of geoid heights with an accuracy of 1-2cm and spatial resolution of

at least 100 km globally. An important application that will benefit from this is the global unification

of the (over 100) existing height systems and consequently the comparability of sea level records

attached to them. GOCE will provide three important components of height unification: highly

accurate potential differences (geopotential numbers), a global geoid- or quasi-geoid-based

reference surface for elevations that will be independent of inaccuracies and inconsistencies of local

and regional data, and a consistent way to refer to the same datum all the relevant gravimetric,

topographic and oceanographic data. The paper summarizes results of a project supported by the

European Space Agency and specifies a scientific roadmap on how GOCE can support world height

system unification.

The Various of Wet Tropospheric Corrections effect on the Regional Sea Level Variability in the

Indonesia Seas. Eko Yuli Handoko, Maria Joana Fernandes, Clara Lazaro For more than 20 years, satellite altimetry has been observing sea level variability over the world.

The study of sea level variation in Indonesia region using satellite altimetry is a challenging topic due

to the coastal effects present in altimeter data, which need to be addressed. Amongst these effects,

the wet tropospheric correction (WTC) is of particular relevance due to its large spatio-temporal

variation.

The aim of this research is to assess the impacts of various WTC in the determination of sea level

change in Indonesia.

Due to its high temporal and spatial variability, the wet tropospheric correction is one of the major

error sources in coastal altimetry. GNSS-derived path delay (GPD) is an algorithm to estimate the wet

tropospheric correction which combines zenith wet delays (ZWD) derived from GNSS, valid

microwave radiometer (MWR) measurements and atmospheric models. Global GPD solutions have

been derived by University of Porto for the main altimetry missions (ERS-1, ERS-2, Envisat,

TOPEX/Poseidon, Jason-1, Jason-2, CryoSat-2 and SARAL/AltiKa) using more than 400 GNSS stations

in coastal and island regions. In particular, a local network of near 30 GNSS stations, located mostly

along of the Sumatera Island, has been used to improve the GNSS coverage in the Indonesian region.


Palma de Mallorca, June 10-12, 2015 In view to determine the most suitable corrections, in this research we present an assessment of the

effect of using these different WTC on sea level studies in the Indonesia region using statistical

analysis of SLA variance function of distance from coast and comparisons with ZTD from GNSS

stations not used in the estimation of the GPD and DComb corrections. Finally, the sea level time

series for the period 1992-2013, computed using the selected set of WTC is presented and compared

with series determined using less accurate corrections

Ocean Bottom Pressure Records at the Permanent Service for Mean Sea Level. Angela Hibbert,

Andrew Matthews, Chris W. Hughes, Mark E. Tamisiea As part of a research effort funded by the U.K. Natural Environment Research Council, the Permanent

Service for Mean Sea Level (PSMSL) has been developing a repository of data from in-situ ocean

bottom pressure recorders (OBPRs) from all possible sources. The data are being processed to a

common format using a consistent methodology so that time series are directly comparable. Efforts

are also being made to ensure that data are accompanied by comprehensive metadata. The OBPR

data are supplied primarily for hourly and daily intervals, making them ideal for studies of tidal to

seasonal variability. In addition, because bottom pressure recorders measure changes in ocean mass,

these data are an ideal complement to GRACE satellite data and a useful accompaniment to sea level

data from tide gauges and altimetry. Consequently, it is anticipated that the PSMSL OBPR repository

will become a valuable product to the scientific community

The Semiannual Oscillation of Southern Ocean Sea Level. Angela Hibbert, Harry Leach, Phil

Woodworth The atmospheric Semiannual Oscillation (SAO) is a half-yearly wave in mean sea level air pressure,

which exhibits equinoctial maxima between 45°S and 50°S and solstitial maxima between 55°S and

65°s, with a phase reversal occurring at around 60°S. Its existence has been attributed to a phase

difference in the annual temperature cycle between mid- and high-latitudes which sets up

meridional temperature and pressure gradients that are largest during September and March,

enhancing atmospheric baroclinicity and inducing equinoctial maxima in the Southern Hemisphere

Westerlies.

In this study, we use harmonic analysis of atmospheric and oceanic Southern Ocean datasets to show

that this atmospheric SAO induces oceanic counterparts in sea level and circumpolar transport. This

aspect of atmosphere–ocean interaction is particularly important, given the capacity of the Antarctic

Circumpolar Current (ACC) to influence regional climate through the exchange of heat, fresh water

and nutrients to each of the major ocean basins. We examine the relative contributions of local and

regional semiannual atmospheric fluctuations as well as the individual influences of atmospheric

pressure and zonal winds in explaining the observed sea level response at Southern Ocean and South

Atlantic tide gauge stations and in altimetry data.



Celebrating 30 Years of the South Atlantic Tide Gauge Network. Angela Hibbert, Pete Foden, Jeff

Pugh, Geoff Hargreaves, Steve Mack, Phil Woodworth It is now 30 Years since NOC Liverpool’s South Atlantic Network came into being (in 1985); at what

was the Institute of Oceanographic Sciences, Bidston. In this poster, we present some of the scientific

and technological advances that have originated from the Network, such as improved understanding

of ACC variability and the development of tide gauge instrumentation to facilitate accurate datum

control. We describe the scientific products currently afforded by the South Atlantic Network and

how they form an important part of the UK contribution to the IOC’s Global Sea Level Observing

System (GLOSS). Finally, we outline proposals for further technological and scientific development of

the Network, including plans to improve the resilience of tide gauge technology in hostile and/or

remote locations.

Observed changes and variability of mean sea-level in the Baltic Sea region during the last 200

years –a review. Birgit Hünicke,l Eduardo Zorita The understanding of the processes driving future trends in sea level presumes an understanding of

long-term variability in the observational period. This requires an accurate assessment of past and

recent change in global and regional sea-level. Recent sea-level trends and decadal variations display

large regional contrasts due to the different physical mechanisms that affect sea level. The Baltic Sea

area, with its complex shoreline, its exposure to the energetic North Atlantic weather and its

proximity to the recent glacial ice-sheets (GIA), provides a challenging research field that requires the

collaboration of multiple scientific disciplines. Baltic Sea level variability is caused by different

climatic and geological factors that render their understanding more difficult than for other areas of

the Earth. Yet this understanding is crucial to predict with reliability the sea-level rise in the Baltic Sea

that will be brought about by anthropogenic climate change.

Here, we present observed changes in mean sea-level variability and the main (climate) drivers for

these changes during the last 200 years by updating and discussing results described in the

framework of the BACC2 project (2nd BALTEX Assessment of Climate Change for the Baltic Sea

Basin).

Baltic Sea level measured relative to land display a strong fingerprint of the GIA effect with sea level

falling by up to 8.2 mm year−1 in the northern parts and slightly rising in parts of the southern Baltic

coasts. Estimates of absolute rise in mean sea-level lie within the range of recent global estimates

(1.3–1.8 mm year−1). The 30-year trends of Baltic Sea tide gauge records tend to increase, but similar

or even slightly higher rates were observed around 1900 and 1950. Baltic Sea level shows higher

values during winter and lower values during spring and this seasonal amplitude increased between

1800 and 2000.

This work is part of the Baltic Earth program (www.baltic-earth.eu) and contributes to the Baltic

Earth Grand Challenge ‘Understanding sea level dynamics in the Baltic Sea’.



Variability of decadal sea-level trends in the Baltic Sea. Sitar Karabil, Eduardo Zorita, Birgit

Huenicke We analysed the variability of the linear decadal sea-level trends in the Baltic Sea over the past 100

years and their connections to trends in the sea-level-pressure (SLP) field. The analysis is limited to

the December-to-February season. We use means of tide gauges from the Permanent Service for

Mean sea level and monthly gridded Sea Level Pressure (SLP) covering the North Atlantic/European

sector from the University of Colorado. To select the tide gauges, we took into account the

geographical distribution and record length retaining Helsinki, Ratan, Stockholm, Kungsholmsfort,

Smogen, Travemunde, Wismar, Warnemunde and Klaipeda. The linear decadal trends were

calculated over gliding 11-year windows of the tide gauges and the SLP grid records. After computing

the decadal gliding trends, we focused on the correlation patterns between each individual tide

gauge and the SLP for every grid separately.

The results show that the tide gauges can be classified into two groups according to their correlation

with the SLP trends. Helsinki, Ratan, Stockholm, Kungsholmsfort, Smogen and Klaipeda display

resembling correlation patterns that have high positive correlation at the south and negative

correlation at the north, with the zero line approximately located at 50 N, and is thus similar to the

typical pattern of the North Atlantic Oscillation. However, Travemunde, Wismar and Warnemunde,

which are located at the southern Baltic Sea coast, display a rather different pattern that shows

negative correlations over the Baltic Sea region, and negligible correlations elsewhere.

The main implication of this study is that the estimation of the possible acceleration of sea-level and

of its statistical significance has to take into account that the variability of decadal sea-level trends

seems to be controlled by very different atmospheric circulation factors, even in this small region.

Forcing of Global Mean Sea Level Interannual variability for the period 1950-2010. Gabriel

Jordà, Francisco Mir Calafat, Mikis Tsimplis Lots of attention has been paid to the forcing of global mean sea level (GMSL) multidecadal and

centennial trends. Conversely, the forcing of GMSL at interannual scales have received less attention,

specially for the pre-altimetric period. In this work we have used a new GMSL reconstruction that

covers the whole XX century and shows high skills in the representation of interannual variability to

investigate the mechanisms forcing GMSL interannual variability. The different components of GMSL

have been estimated from different observational based datasets. Our results suggest that the main

driving mechanism is the transfer of water from land to the ocean through changes in the

hydrological cycle. The second driving mechanism is thermal expansion while the storage of water in

the atmosphere barely contributes. The results also show that there is no particular continent

dominating the changes in land water storage at interannual scale. Finally, some discussion about the

reliability of different databases will be presented.

Nordic Sea Level – Analysis of PSMSL RLR Tide Gauge data. Per Knudsen, Ole Andersen, Carlo

Sørensen Tide gauge data from the Nordic region covering a period of time from 1920 to 2000 are evaluated.

63 stations having RLR data for at least 40 years have been used. Each tide gauge data record was

averaged to annual averages after the monthly average seasonal anomalies were removed.


Palma de Mallorca, June 10-12, 2015 Some stations lack data, especially before around 1950. Hence, to compute representative sea level

trends for the 1920-2000 period a procedure for filling in estimated sea level values in the voids, is

needed.

To fill in voids in the tide gauge data records a reconstruction method was applied that utilizes EOF.s

in an iterative manner. Subsequently the trends were computed. The estimated trends range from

about -8 mm/year to 2 mm/year reflecting both post-glacial uplift and sea level rise.

An evaluation of the first EOFs show that the first EOF clearly describes the trends in the time series.

EOF #2 and #3 describe differences in the inter-annual sea level variability with-in the Baltic Sea and

differences between the Baltic and the North Atlantic / Norwegian seas, respectively.

Variability of the ocean bottom pressure along the Gulf of Cadiz and its effect on the sea level

spatial distribution. Irene Laiz, Marta Marcos, Jesús Gómez-Enri, Evan Mason, Begoña Tejedor,

Alazne Aboitiz, Pilar Villares A high resolution regional ocean model (Regional Ocean Modeling System, ROMS) was used to

explore the spatial patterns of bottom pressure anomalies within the Gulf of Cadiz as a function of

depth and time together with a simple conceptual model that relates temperature changes to

bottom pressure variations. Moreover, daily maps of gridded altimeter-derived sea level anomalies

were used to analyze how the bottom pressure variations at depths below and above the steric

anomalies can affect the sea level spatial distribution at regional scales.

Satellite altimetry Calibration/Validation at the Australian Bass Strait site in the context of the

new missions Jason-3 and Sentinel-3. Legresy B., C. Watson, J. Church, N. White, J. Beardsley, J.

Andrewartha The Bass Strait satellite altimetry validation site has been one of 3 reference sites spread around the

world for the Topex-Poseidon and Jason satellite altimeter series since the 1990s. There, the

absolute calibration attained is at the cm level contributing importantly to the altimetry systems

absolute bias estimation and to their drifts monitoring.

In 2015-2016 two new accurate satellite altimetry missions will be launched and need calibration

validation. The method developed over the years for Jason involves tide gauges, moorings where we

measure temperature, salinity, pressure and currents, atmospheric measurements and operational

models (ACCESS) to extend measurements and corrections from coastal tide gauges to the cal/val

site 25km off the coast under the satellite track. GPS buoys are regularly deployed to reference the in

situ sea level measurements to the same datum as the satellites and estimate instruments bias and

drifts. While the system is quite operational in view of the Jason-3 satellite, the newcomer Sentinel-3

will have a different ground track, repeat time, and measurement mode. We will show the overall

calibration system and the results over the TOPEX-Jason period. We will also show the extension and

improvements we are developing in the frame of Jason-3 and Sentinel-3 new missions. In particular,

we investigate the possibility and capability of a regional ocean model to test the sensitivity and

extend the present system with a mooring under the Jason track to a Sentinel-3a crossover ~10km

away.



Sensitivity of sea-level rise reconstruction from 1900 to present. Legresy B. , J. Church , N.

White, D. Monselesan and A. Slangen We reconstruct the sea level rise from 1900 to present, revisiting the reconstruction from Church and

White (2011). We update this reconstruction, which is based on satellite altimetry learning and

projects tide gauges records on the derived modes of variability. We performed or repeated a

number of sensitivity tests on the learning period, number of modes, and inversion parameters. We

also tested the sensitivity to variations in the mathematical method, in the learning process as well as

the number of tide gauges, vertical crustal movement and contemporary mass load redistribution at

the surface of the Earth. For global mean sea level, the length of the learning period seems to be of

little importance beyond one decade. The same applies, for example, to the number of modes, it

does not improve the solution to use more than 4 modes for the longer records of global mean sea

level. We show sensitivity results for the long term global mean sea level and for regional mean sea

level over the 1950-2015 period. We revisit the error budget. Finally, we compare to other

reconstructions in view of this sensitivity analysis.

Relative sea-level change along the Italian coast during the late Holocene and projections for

2100: Coastal plain impacts based on high-resolution DTMs and geodetic data. Valeria Lo

Presti., Fabrizio Antonioli , Alessandro Amorosi , Marco Anzidei , Gianni De Falco , Alessandro

Fontana , Giuseppe Fontolan , Giuseppe Mastronuzzi , Enrico Serpelloni , Antonio Vecchio Sea-level data are used to provide projections of sea-level change in Italy for the year 2100 by adding

isostatic and vertical tectonic components to the IPCC 2013 and Rahmstorf projections. We focus on

the North Adriatic coast and Venice, subsiding at -0.7 mm\yr, the tectonically stable Cagliari and

Oristano coastal Plain (Sardinia) and the slightly uplifting area of Mar Piccolo (Taranto, Apulia). We

used high-resolution DTMs to depict a multitemporal flooding scenario up to 2100.

Data of sea level indicators are compared with the predicted sea-level curves providing estimates of

the vertical tectonic contribution to the relative sea-level change. The results are based on the most

recent ANU model and discussed against available GPS data for present day vertical land motion and

sea level trend from tide gauge data. On the basis of eustatic, tectonic and isostatic components to

sea-level change, projections are offered for those coastal plains currently placed at elevations very

close to present-day sea level.

Sea Level Oscillations in The Baltic Sea: From Minutes to Centuries. Igor P. Medvedev, Alexander

B. Rabinovich, Evgueni A. Kulikov Various types of processes determine sea level changes in the Baltic Sea: tectonic motions, multiyear

climatic variations, the pole tide, seasonal oscillations, tides, storm surges and seiches. We examined

the formation mechanisms and basic properties of each of these oscillations covering a wide range of

periods: from minutes to centuries. The Baltic Sea is connected to the North Sea and Atlantic Ocean

through narrow and shallow Danish straits, which act as a low-pass filter, strongly suppressing high-

frequency processes but allowing low-frequency processes to pass freely through. As a result,

relatively short-period oscillations (with periods 3-4 months) are induced by the waves coming from

the North Sea. Tides, storm surges and seiches are of the first type and have a character of “proper

oscillations”; they are formed in the Baltic Sea as a whole, or gulfs and bays of the sea. Similar


Palma de Mallorca, June 10-12, 2015 formation mechanisms of these processes lead to strong similarity in their physical properties.

Different types of oscillations superimpose and interact with each other. In particular, seiches

increase the storm surge heights at the head of the Gulf of Finland; the fundamental eigen mode of

this gulf, with a period of ~27 hrs, is the main reason for catastrophic Saint Petersburg floods and

amplification of diurnal tidal constituents. Radiational tides appear to play an essential role is some

parts of the sea, including Narva and Daugavgriva; moreover, in Curonian Lagoon astronomical

(gravitational) tides are not observed at all, while the radiational tide caused by the sea breeze, is

substantial. Climatic fluctuations, seasonal sea level oscillations and the pole tide are all “induced

oscillations”. They have very similar spatial structure and are found to be strongly influenced by

atmospheric processes over the Northeast Atlantic.

Tides in the Baltic, Black and Caspian Seas. Igor P. Medvedev, Alexander B. Rabinovich, Evgueni

A. Kulikov Tides are the main type of sea level variability in the World Ocean. However, tidal signal from the

World Ocean almost do not penetrate into isolated inland seas, such as the Black, Caspian and Baltic

seas. Consequently, only the directly forced tides are formed in these seas. Tides are weak in these

seas in comparison with the longwave background noise; thus long observation time series are

necessary to estimate tidal constituents precisely. Such particular series were used in these studies:

up to 123 years in the Baltic Sea, and up to 38 years in the Black and Caspian seas. High-resolution

spectral analysis revealed fine structure of well-defined spectral peaks at tidal frequencies. Diurnal

radiational tidal constituent S1 (1 cpd) and high-frequency radiational tidal peaks, multiples of a solar

day (3, 4, 5, 6 and 8 cpd), were identified in some areas of the seas. Sea-breeze winds are supposed

to be the main factor inducing these oscillations. Harmonic analysis of tides for individual yearly

series with consecutive vector averaging over the entire observational period was applied to

estimate mean amplitudes and phases of major tidal constituents, the maximum tidal height, the

type of tides and the spatial structure of tides. Eigen oscillations of the respective basins (sea seiche

modes), with periods close to diurnal and semidiurnal, play the key role in formation of the

corresponding tides.

The Annual Global-Mean Thermosteric Height Budget. Christopher G. Piecuch, Rui M. Ponte Changes in global-mean thermosteric height (GMTH) reflect expansion or contraction of the oceans

due to thermally induced ocean density changes. While past works diagnose GMTH changes using in

situ data or remote measurements, understanding of physical processes contributing to the GMTH

changes is lacking. Unlike heat, density (or buoyancy) is not conserved in the ocean—a consequence

of the nonlinear nature of the seawater equation of state. While GMTH can be affected by surface

heat fluxes, it can also be influenced by net creation or destruction of buoyancy by ocean heat

transports across constant-pressure and -temperature surfaces.

To investigate the annual GMTH budget, we first perform comprehensive diagnostics of the ECCO-

Production Release 1 ocean state estimate. Estimated annual GMTH changes are wholly

compensated by net surface buoyancy flux (NSBF) due to surface heat exchange. Ocean heat

transports do not contribute mainly because annual ocean heat content anomalies are mostly stored

in the upper ocean (and are not transported along strong temperature gradients). These results

suggest that, for the annual frequency, the GMTH budget can be diagnosed observationally from


Palma de Mallorca, June 10-12, 2015 knowledge of the temperature and NSBF fields. To corroborate these findings, and also to gauge the

consistency of available datasets, we compare to GMTH and NSBF annual cycles computed based on

different observational products. The amplitude and phase of annual cycle in GMTH derived from

Argo gridded data are nearly indistinguishable from those derived from NSBF based on OAFlux

surface heat exchanges, supporting findings from the state estimate. Additional analyses consider

annual cycles in GMTH estimated from altimetry and GRACE, and in NSBF determined from NOCS

v2.0 marine surface fluxes along with satellite sea-surface temperature. Results highlight the

usefulness of GMTH as a measure of the quality of surface flux data.

Deriving sea level from tide gauges. Jens Schröter, Manfred Wenzel, Klaus Grosfeld, Roelof

Rietbroek Past sea level is frequently derived from tide gauge measurements. A common approach is to relate

relative tide gauge data to geocentric measurements derived from satellite altimetry.

We present two methods on how to relate the different reference frames and what consequences

can be expected from different assumptions about vertical land movements.

The South Atlantic sea level variability. Raisa de Siqueira Alves, Angela Hibbert and Harry Leach Sea Level varies on different time and spatial scales and due to a large range of forcing processes,

such as tides, weather, the variability described by atmospheric climate modes and ocean processes.

In the South Atlantic ocean, little is known about how the sea level responds to these processes,

although some recent works by Sterl & Hazeleger (2003), Lubbeck et al. (2010) and Nnamchi et al.

(2011) indicate an intrinsic variability in this ocean. Thus, in this project, we aim to assess the

contributions of atmospheric climate modes, sea surface temperature and atmospheric pressure to

sea level variation in this ocean. We used the AVISO combined altimetry dataset from 10/1992 to

01/2011, published indices of climate modes, atmospheric reanalysis datasets of surface pressure,

sea surface temperature from HadISST and tide gauge data from the PSMSL data base. The altimetry

and tide gauge data were analyzed separately, but using the same methodology. First we divided

their time series into annual cycle and residuals. Then, from the residuals, we calculated the mean

sea level trend, performed an EOF analysis to characterize the sea level natural modes of variability,

correlated them with the atmospheric indices and corrected the atmospheric pressure and

temperature effect. A sea level dipole was present in the EOF analyses of the tide gauge data and this

led us to calculate a new atmospheric index, called the South Atlantic Index (SAI), to correlate with

the sea level variation. As a result, the SAI, together with the Pacific-South America Mode indices and

the Southern Oscillation Index, were always significantly correlated with the sea level eigenvectors,

even after the inverse barometer and thermal effect correction. The residuals contributed the most

to the variance of the sea level in the South Atlantic, especially near the Confluence Zone and

Agulhas Retroflection area. Yet, this variance was not explained by the pressure or temperature

effects studied in this work.



Closing the gap between regional and global sea level in the Bay of Bengal. Bernd Uebbing,

Roelof Rietbroek, Sandra-Esther Brunnabend, Jürgen Kusche A thorough understanding of sea level rise requires the quantification of the underlying drivers. Using

satellite gravimetry and radar altimetry, we can split up the global mean sea level budget into

components induced by mass changes (e.g. melting of glaciers, ice-sheets and water cycle variations)

and volumetric changes (thermo and halosteric variations). However, global sea level rise does not

necessarily match up with regional estimates of sea level change. This becomes apparent when

regional trend maps of altimetry data or individual tide gauges, are compared with global mean sea

level estimates.

In this study, we use satellite gravimetry from GRACE and radar altimetry from Jason-1 and Jason-2

to break down the sea level budget in the Bay of Bengal. The data is combined in a joint inversion

scheme, where individual contributions to sea level are parametrized by a set of physically

determined a priori 'fingerprints' whose time variations are then estimated from the data.

Regional estimates of total sea level rise in the Bay of Bengal revealed sea level rise of twice the

global rate and are subsequently compared with global estimates and altimetry. Furthermore, we

investigate the individual components from mass and steric sea level. We find that 20% of the total

sea level rise of about 5.8 mm/yr (2002.5-2014.5) in the Bay of Bengal are related to mass changes,

while the remaining 80% are attributed to steric changes. The dominant contribution from the latter

in the Bay of Bengal is confirmed by independent data from ARGO floats, and oceanographic

modelling.

How long does it take to measure a trend in ocean bottom pressure?. Joanne Williams, Chris

Hughes, Mark Tamisiea Ocean bottom pressure, measured at only a few locations, can theoretically be used to derive global

mean mass changes in the ocean. However bottom pressure sensors suffer from non-linear drift, so

cannot currently be used to measure trends. Therefore we investigate an alternative method to

measure the small bottom pressure signal as the difference between the two large signals of steric

pressure (from a hydrographic mooring) and sea-surface height (from altimetry). In many places

bottom pressure has much smaller variability than the corresponding sea-level signal, and so the

time required to detect a trend of given magnitude is much shorter. We test the method on data

from the Rapid mooring array at 26N in the Atlantic, and determine how many years would be

required to detect a trend in bottom pressure from this technique.

Modelling Sea Level Changes

Oral Presentations



Long-Term Internal Variability Effects on Centennial Dynamic Sea Level Projections. Mohammad

H. Bordbar Thomas Martin, Mojib Latif, Wonsun Park The Earth’s surface is warming in response to anthropogenic emissions of greenhouse gases,

especially carbon dioxide (CO2). Sea level rise is one of the most pressing aspects of global warming

with far-reaching consequences for coastal societies. However, sea level rise did and will strongly

vary from coast to coast. Here we investigate the long-term internal variability effects on centennial

projections of dynamic sea level (DSL), the local departure from the globally averaged sea level. A

large ensemble of global warming integrations was conducted with a climate model, where each

ensemble member was forced by identical CO2-increase but started from different atmospheric and

oceanic initial conditions taken from an unforced millennial control run. In large parts of the mid- and

high latitudes, the ensemble spread of the projected centennial DSL trends is of the same order of

magnitude as the globally averaged steric sea level rise, suggesting internal variability cannot be

ignored when assessing 21st century DSL changes. This conclusion is also supported by analyzing

projections with other climate models. The ensemble spread is strongly reduced in the mid- to high

latitudes if only the atmospheric initial conditions are perturbed; suggesting uncertainty in the

projected centennial DSL trends there is largely due to the lack of ocean information. Thus climate

model projections of regional sea level would benefit from ocean initialization.

Interannual Predictability of North Atlantic Sea Level Dynamics. Robert Fraser, Laure Zanna,

Chris Wilson A large degree of uncertainty remains in both the temporal and spatial variability of regional sea level

predictions. This study aims to constrain the uncertainty, due to both the atmospheric and ocean

states, by examining the dynamics and predictability of sea surface height (SSH) in the North Atlantic

on interannual timescales. An evaluation of the typical timescales of SSH predictability in an idealised

model set up of a flat bottomed, barotropic double gyre has been undertaken. Moreover, the

sensitivity of the SSH predictability to applied wind stress perturbations of differing magnitudes has

been examined. The timescales of predictability present were evaluated by using linear inverse

modeling techniques to represent the system by a statistical, yet dynamical, model. It was found that

potential for interannual predictability exists and is largely located both in the jet region and in the

vicinity of the western boundary. In order to investigate the mechanism behind this interannual

variability and predictability, further analysis of the ocean momentum budget was carried out with a

focus on the eddy-mean flow interaction. Results indicate that further studies, where particular

emphasis is placed on sea level anomalies near the coast, could inform measurements by examining

which time and spatial resolutions are needed to obtain relevant measures of predictability

Seasonal coastal sea-level prediction using a dynamical model. John A. Church, Peter C.

McIntosh, Elaine R. Miles, Ken Ridgway, Claire M. Spillman Many millions of people living in coastal regions are vulnerable to sea-level extremes resulting from

the combined effect of storm surges, seasonal and interannual sea-level anomalies, and long term

sea-level rise. Accurate coastal sea-level predictions would assist in preparing for extreme events.

While sea-level rise has been a major focus of international research, and there are a number of

operational storm surge prediction programs, the influence of interannual and seasonal sea-level

anomalies has received less attention, with statistically-based operational prediction schemes


Palma de Mallorca, June 10-12, 2015 available at only a few locations in the western Pacific Ocean. Here, we demonstrate that forecasts of

coastal sea-level anomalies from the dynamical Predictive Ocean Atmosphere Model for Australia

(POAMA) have significant skill throughout the equatorial Pacific and along the eastern boundaries of

the Pacific and Indian oceans. POAMA forecasts for the western Pacific have greater skill than

statistical forecasts from both a Markov model and canonical correlation analysis. Our results

demonstrate the capability of POAMA to provide earlier and more skilful warnings of seasonal sea-

level changes for vulnerable coastal communities.

Regional Budgets of Sea Level in the ECCO-Production Release 1 Ocean State Estimate.

Christopher G. Piecuch, Rui M. Ponte, Gael Forget, Ichiro Fukumori We consider regional sea level from the Estimating the Circulation and Climate of the Ocean (ECCO)-

Production Release 1 state estimate. The solution is a physically consistent estimate of the global

ocean circulation and ice state over 1992-2011; it incorporates millions of ocean observations into an

ocean general circulation model framework. The consistency of the estimate facilitates

decomposition of sea level into steric-height (density) and bottom-pressure (mass) contributions; it

also allows for unambiguous identification of the physical processes impacting the evolution of steric

height and bottom pressure. Steric anomalies can be ascribed to advection, diffusion, and forcing of

heat and salt; bottom pressure can be partitioned into barotropic and baroclinic components.

We focus on interannual and decadal anomalies. In deep basins at low and middle latitudes, sea level

is controlled by steric height, but bottom pressure contributes at high latitudes and over shelf seas.

Steric anomalies generally reflect a complex interplay between surface forcing and vertical and

horizontal advection and diffusion of heat and salt. Thermosteric variations predominate in the

tropical Pacific and Indian Oceans, whereas halosteric variations are important in polar regions

characterized by sea ice. Vertical heaving controls steric changes only over small parts of the

northeastern North Pacific and southeastern South Pacific Oceans. Influences of advection and

forcing are anticorrelated along the equator and over strong currents, hinting at coupling or damping

effects. Mixing is important near sites of deep convection and mode water formation, for example, in

the Labrador, Greenland, Irminger, and Norwegian Seas. Bottom pressure at middle and high

latitudes mostly reflects barotropic processes, but baroclinic effects can be important at low

latitudes.

Results demonstrate the usefulness of incorporating observations into a consistent model framework

for quantifying mechanisms of sea-level change.

Imprints of oceanic intrinsic variability on altimetric measurements: an OGCM study. Guillaume

Sérazin, Thierry Penduff, Laurent Terray, Bernard Barnier, Jean-Marc Molines Recent Ocean Global Circulation Model studies have highlighted the ability of the turbulent ocean to

spontaneously generate low-frequency variability of sea-level over a wide range of spatial scales

(Serazin et al., 2015). In terms of variance in the interannual band (i.e. from 1.5 to 20 years), this

intrinsic variability is very comparable to the total hindcasted variability at small scales ( 12°). This

low-frequency intrinsic variability may be seen in the 22 year record of altimetric data and we

propose a method to isolate some intrinsic features in this dataset based on a high-pass spatial

filtering.


Palma de Mallorca, June 10-12, 2015 This study also focus on timescales longer than 20 years using a 300 year long 1/4° simulation, which

shows that the ocean spontaneously generates decadal sea-level fluctuations in eddy-active regions.

It is shown that this ocean-only variability may have an imprint on observed regional sea-level trend,

especially in the ACC and in the Western Boundary Current areas. The incertitude on sea-level trends

induced by truncating this decadal intrinsic variability is comparable to the one estimated from

Global Coupled Models in which the oceanic intrinsic component is not taken into account yet.

A near-uniform fluctuation dominating sea level and ocean bottom pressure variations across

the Arctic Ocean and the Nordic Seas. Ichiro Fukumori, Ou Wang, William Llovel, Ian Fenty, Gael

Forget Across the Arctic Ocean and the Nordic Seas, a basin-wide mode of sea level and ocean bottom

pressure fluctuation is identified using satellite and in situ observations in conjunction with a global

ocean circulation model and its adjoint. The region is central to studies of sea level change because it

is where the ocean interacts with the cryosphere including Greenland’s ice sheet. The basin-wide

variation extends across the interconnected deep ocean basins of these Arctic seas with near-

uniform amplitude and phase. The fluctuation is depth-independent and dominates the region’s

large-scale variability from sub-monthly to interannual timescales. The fluctuation results from

bifurcating coastally trapped waves generated by winds along the continental slopes of the Arctic

region and its neighboring seas, including the North Atlantic Ocean. The winds drive Ekman transport

between the shallow coastal area and the deep ocean basins, creating sea level anomalies of

opposite signs in the two regions. The anomalies rapidly propagate away as barotropic coastally

trapped waves that subsequently bifurcate at the shallow straits connecting the Arctic region with

the rest of the globe. Anomalies that enter the deep Arctic basins equilibrate uniformly across the

domain, isolated from neighboring shallow variations, due to the basins’ homogeneous depth-

integrated planetary potential vorticity distribution. The study, from a technical perspective,

illustrates how a thoughtful application of the adjoint technique provides an explanation of physics

that statistical analysis of model results and/or observations cannot. Whereas correlation does not

imply causation, adjoints do.

Pacific sea level trends: internally or externally forced? Felix Landerer A prominent sea level rise pattern in the Pacific Ocean – large increases of 12 mm/yr in the West and

near-stagnant levels in the East – has been observed with satellite altimetry since the 1990s. A

significant fraction of this dipole trend pattern correlates well with the Pacific Decadal Oscillation

(PDO), a large-scale mode of internal climate variability. However, the PDO cannot fully account for

the Western Pacific Ocean trend pattern. Whether or not the remaining non-PDO pattern can be

linked to an anthropogenic influence has been discussed in several recent studies. Here, we use a

large ensemble of CMIP5 20th century simulations (more than 150 runs from 27 different GCM

setups) to further investigate the role and contribution of the PDO and other modes of equatorial

variability to Pacific sea level change patterns. Specifically, we focus on 20-year trend patterns since

1950, and attempt to isolate and attribute an externally forced sea level pattern by removing sea

level trend contributions from internal variability to test if the remaining patterns become more

consistent across the models, and thus support the notion of a detectable common externally forced

sea level change since 1990.



Spatial scales and the detection of externally forced signals in regional sea surface height in

CMIP5 models. Kristin Richter, Ben Marzeion Various detection and attribution studies have found an anthropogenically forced signal in global

thermosteric sea surface height. However, detection on regional to local scales is hindered due to the

increased magnitude of internal variability on smaller spatial scales. Recent studies attempted to

quantify local internal variability to assess the time of emergence of an externally forced signal in

climate simulations. They found that, in regions of elevated internal variability such as the western

tropical Pacific Ocean, it can take several decades for a forced signal to emerge from the background

noise.

Here, we investigate the spatial scales that are necessary to detect an externally forced signal within

a selected fixed time period. Using control simulations with no evolving forcing, we quantify the

magnitude of regional internal variability depending on the degree of spatial averaging. We test

various averaging techniques such as zonal averaging, ocean basin averages and averaging gridpoints

within a selected radius. Historical and 21st-century simulations are treated the same way. By

comparing the results from control simulations with scenario simulations, the procedure allows us to

estimate to what degree the data has to be averaged spatially in order to detect a forced signal

within a certain period of e.g. 20 years (the period with available global sea surface height

observations). Having identified, for each grid point, the averaging radius that is necessary to detect

an external signal during the past 20 years, the results can be applied to observations and it can be

assessed on which spatial scales regional detection and attribution studies may yield meaningful

results.

Worst-case scenarios for sea level rise from ice sheet melt. Carmen Boening, Nicole Schlegel,

Michael Schodlok, Daniel Limonadi, Eric Larour, Michael M. Watkins Uncertainties in current global mean sea level rise (SLR) estimates for the next 100 years are fairly

large and complicate decision making processes for coastal planning. Current estimates of SLR by

2100 range between 30 cm and 2 m implying very different ramifications for planning strategies over

the next decades. The main source of uncertainty in these estimates is the future of the major ice

sheets, Greenland and Antarctica, as they hold close to 70 m of fresh water that have a large

potential impact on SLR in case of a collapse. Here, we explore upper bounds for SLR caused by ice

sheet melt/collapse by evaluating worst-case scenario runs from state-of-the-art ice sheet and ocean

models of Antarctica and the Southern Ocean. As a reference, we performed a control run, forced

with a mean climatology of surface mass balance and ice shelf basal melt rates, to assess the relative

change compared to the worst-cases; SLR from the control is ~0.2m in the next 100 years. The first

worst-case we analyzed is: the instantaneous removal of all floating ice shelves, the resulting effects

on grounding line position and ice sheet velocities given missing backstress, and consequential SLR

over the next 100 years. A second experiment explores potential mechanisms needed to remove the

ice shelves by increasing melt rates by a factor of 100. First results indicate that both scenarios have

significant impacts on SLR over the next 100 years (remove ice shelves: 1.1 m; melt rate x 100: 2.2

m). Thus, it is important to explore the likelihood of these scenarios. In comparison, forcing the

model with maximum melt rates from the last 20 years, which are much smaller than melt rate x 100,


Palma de Mallorca, June 10-12, 2015 lead to a SLR of 0.25 m over 100 yrs, a result that is much closer to the control run and the lower

limit of SLR.

Asymmetry in regional sea level rise projections due to skewed ice sheet contributions. Renske

de Winter, Thomas Reerink and Roderik van de Wal In the latest IPCC assessment report it is assumed that the uncertainties around sea level rise (SLR)

projections are Gaussian distributed, implying that uncertainties are equally likely for both higher

and lower probabilities. However, expert judgment suggests that, as a result of ice sheet dynamics,

the contribution of ice sheet mass loss to SLR has large uncertainties towards high values. Hence, the

probability density function (PDF) of the ice sheet mass loss is skewed to higher values. In this study

we analyse how asymmetric distributions for ice sheet dynamics influence the uncertainty in regional

SLR.

The effect of skewed contributions for ice sheet dynamics are determined by combining the PDFs of

the projected contributions to SLR for Greenland, West and East Antarctica, with the PDF for regional

SLR due to climate change effects, including gravitational and rotational effects.

Near the West Antarctic and the Greenland ice sheet the new combined PDF is skewed towards

negative values due to the gravitational effect; mass loss of an ice sheet results in a sea level drop in

the vicinity of this ice sheet. For most other areas of the world, the projected PDF of SLR becomes

wider and skewed towards higher SLR values leading to increased risks of high sea level rise.

As we are mainly interested in the changes in the upper tail of the distribution, we analyse our

results by comparing the difference in mean with difference of the upper 95, 97 and 99% interval.

Averaged over the ocean the additional increase in sea level rise are 0.19, 0.22 and 0.28 m for the

different intervals. Locally, with the east coast of the US as an example, the increase in the tail

amounts up to 0.24, 0.28 and 0.36 m for respectively the 95%, 97% and 99% intervals.

Posters

Analysis of the regional pattern of sea level change due to ocean dynamics and density change

for 1993–2099 in observations and CMIP5 AOGCMs. Roberto A. F. Bilbao, Jonathan M. Gregory,

Nathaelle Bouttes Predictions of twenty-first century sea level change show strong regional variation. Regional sea level

change observed by satellite altimetry since 1993 is also not spatially homogenous. By comparison

with historical and pre-industrial control simulations using the atmosphere–ocean general circulation

models (AOGCMs) of the CMIP5 project, we conclude that the observed pattern is generally

dominated by unforced (internal generated) variability, although some regions, especially in the

Southern Ocean, may already show an externally forced response. Simulated unforced variability

cannot explain the observed trends in the tropical Pacific, but we suggest that this is due to

inadequate simulation of variability by CMIP5 AOGCMs, rather than evidence of anthropogenic

change. We apply the method of pattern scaling to projections of sea level change and show that it

gives accurate estimates of future local sea level change in response to anthropogenic forcing as

simulated by the AOGCMs under RCP scenarios, implying that the pattern will remain stable in future


Palma de Mallorca, June 10-12, 2015 decades. We note, however, that use of a single integration to evaluate the performance of the

pattern-scaling method tends to exaggerate its accuracy. We find that ocean volume mean

temperature is generally a better predictor than global mean surface temperature of the magnitude

of sea level change, and that the pattern is very similar under the different RCPs for a given model.

We determine that the forced signal will be detectable above the noise of unforced internal

variability within the next decade globally and may already be detectable in the tropical Atlantic.

Global reconstructed daily storm surge levels from the 20th century reanalysis (1871-2010).

Alba Cid, Paula Camus, Sonia Castanedo, Fernando Méndez, Raúl Medina The study of global patterns of wind and pressure gradients, and more specifically, their effect on the

sea level variation (storm surge), is a key issue in the understanding of recent climate changes. The

local effect of storm surges on coastal areas (zones particularly vulnerable to climate variability and

changes in sea level), is also of great interest in, for instance, flooding risk assessment.

Studying the spatial and temporal variability of storm surges from observations is a difficult task to

accomplish since observations are not homogeneous in time and scarce in space, and moreover,

their temporal coverage is limited. The development of a global storm surge database (DAC, Dynamic

Atmospheric Correction by Aviso, Carrère and Lyard, 2003) fulfils the lack of data in terms of spatial

coverage, but not regarding time extent, since it only includes last two decades (1992-2014).

In this work, we propose the use of the 20CR ensemble (Compo et al., 2011) which spans from 1871

to 2010 to statistically reconstruct storm surge at a global scale and for a long time period. Therefore,

the temporal and spatial variability of storm surges can be fully studied and with much less effort

than performing a dynamical downscaling.

The statistical method chosen to carry out the reconstruction is based on multiple linear regression

between an atmospheric predictor and the storm surge level at daily scale (Camus et al., 2014). The

linear regression model is calibrated and validated using daily mean sea level pressure fields (and

gradients) from the ERA-interim reanalysis and daily maxima surges from DAC.

Hence, this work provides a daily database of maximum surges that can be used for the scientific

community to improve the knowledge on historical storm-surge conditions.

Nonlinear model of the long-term sea-level fluctuations in the Caspian Sea. Anatoly V. Frolov Long-term sea-level fluctuations in the Caspian Sea (CSL) are considered as the output process of the

essentially nonlinear system with negative and positive feedback. The elaborated model is based on

the analysis of CSL fluctuations and water balance data for 1880-2013. The model also takes into

account the water outflow from the Caspian Sea into Garabogazköl Bay, which is the function of CSL.

According to the model, the probability density function (PDF) of the CSL is derived as the solution of

the Fokker-Planck-Kolmogorov equation. We used this model to examine the influence of the

mathematical expectation of inflow on the CSL PDF. It is shown that the bilinear properties of the CSL

PDF can exist only for a certain range of mean inflows. Some applied aspects of the CSL modeling are

also discussed.



Sea Level Complexity in Observations And Models. M. Karpytchev, M. Becker, M. Marcos, S.

Jevrejeva, S. Lennartz-Sassinek Most tide gauge records can be represented as outcomes of stochastic power-law process with a

Hurst exponent 0.5 indicating the presence of long-term time correlations. The long-term correlated

records manifest a specific long-term persistence behavior: large events well above the average are

more likely to be followed by large events, and small events by small events. The spatial variations in

the magnitude of the Hurst exponent in the observed sea level records seem to follow regular

patterns that is

potentially important for understanding sea level changes and for developing an adequate noise

model required by an accurate sea level trend estimation. We compare the spatial distribution of

the Hurst exponents derived from the observations with those predicted by the global climate

models and discuss the possible links between the scaling and the main features of the global ocean-

atmosphere circulation.

Explaining the spread of CMIP5 climate models in global-mean thermosteric sea level rise over

the 20th and 21st centuries. B. Meyssignac, A. Melet The ocean stores more than 90% of the energy excess associated with anthropogenic climate

warming. The resulting warming and thermal expansion of the ocean is a leading contributor to sea

level rise. Confidence in projections of global mean sea level rise therefore depends on the ability of

climate models to reproduce ocean warming and induced global mean thermosteric sea level

(GMTSL) over the 20th century. This study aims at explaining and trying to reduce the spread of

GMTSL across climate models of the Coupled Models Intercomparison Project Phase 5 (CMIP5) over

the 20th and 21st centuries.

We first show that the GMTSL rise computed from climate models is approximately proportional to

the radiative forcing. The constant of proportionality mostly depends on the climate feedback

parameter and the ocean heat uptake efficiency. From that linear relationship, we show that the

spread in the net top-of-atmosphere radiative flux (N) explains most of the spread in projections of

the GMTSL. The inter-model spread of N is itself mostly explained by the spread in the radiative

forcing changes while the spread in climate feedback parameter and ocean heat uptake efficiency

play a smaller role.

We then compare GMTSL from climate models to observational estimates over the 1961-2005

period. Although the model-ensemble mean is within the uncertainty of observations, a significant

number of models consistently overestimate or underestimate the observed GMTSL rise. The

contribution of the deep ocean (below 700 m depth) to GMTSL is largely spread among climate

models (33+/-28% over 1900-2005). Selecting the sub-ensemble of models that conserve the energy

in the climate system and are within the observational estimates of GMTSL reduces that spread and

leads to a contribution of 35+/-10%.

The uncertainty in projected GMTSL in 2100 can also be reduced with a selection of climate models

based on the comparison of the climate feedback parameters, ocean heat uptake efficiencies and

20th century radiative forcings of the sub-ensemble of climate models that best reproduce the

observed GMTSL over 1961-2005.



Multi-annual predictability of regional sea level in a global climate model. C. D. Roberts, N.

Dunstone. L. Hermanson, M. Palmer, D. Smith Recent work has demonstrated that some aspects of regional sea level are predictable on seasonal

time scales using a global climate model initialized with an appropriate ocean state (Miles et al.

2014). However, the predictability of regional sea level on multi-annual time-scales has yet to be

evaluated. Here, we present an initial assessment of the predictability in time-mean dynamic sea

level using five-year hindcasts from the latest configuration of the UK Met Office Decadal Prediction

System (DePreSys3), a coupled ocean-atmosphere-sea ice model with an eddy-permitting ocean

resolution. Hindcasts are initialized from a model assimilation of a full-depth ocean analysis and skill

is evaluated against satellite altimetry and tide-gauge reconstructions of sea surface height.

Miles et al. "Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical

model." Climate Dynamics 43.7-8 (2014): 2131-2145.

Statistical modeling of Sea Level for regional semi-enclosed basins. Luca Scarascia and Piero

Lionello This study analyzes the deviations of semi-enclosed regional basins from the global mean sea level

(SL). It considers three cases: the Baltic, Adriatic and Black Sea. The aim is to develop a statistical

model for estimating to which extent the SL of these basins will depart from the mean global level in

the future. The past SL of these three basins can be estimated from tide gauge records that are

available in the PSMSL database (13, 7, 4 tide gauges in the Baltic Sea, Adriatic Sea and Black Sea,

respectively). SL data are considered after the subtraction of the Inverse Barometer (IB) effect. By a

statistical method, based on PCA and Least Squares Method (LSM), a continuous time series Baltic

and Adriatic Sea level from 1901 to 2009 has been obtained. Lack of data (in the first part of 20th

century and in the last decade before 2009) and substantial disagreement in several parts of the

records prevent obtaining the analogously continuous results for the Black Sea. A multivariate linear

regression model is used to investigate the link between SL anomaly, computed as the difference

between the regional SL and global SL, and three large scale climate variables (sea level pressure, air

temperature and precipitation). Mean sea level pressure is found to be the main factor reproducing

the past SL variability. The linear model at a monthly scale provides a quite good reconstruction of

the past variability for Baltic and Adriatic Sea, but with substantial differences in the reconstruction

skill between cold and warm seasons. The skill of the model is substantially worse for Black Sea than

for the two other basins. The same linear model forced by CMIP5 model simulations is used for SL

projections until 2100.

This study is part of the activities of RISES-AM project (FP7-EU-603396).

Projections of 21st Century Sea Level Changes for Norway. Matthew J. R. Simpson, J. Even Ø.

Nilsen, Oda Ravndal, Kristian Breili, Halfdan P. Kierulf, Holger Steffen, Eystein Jansen, Hilde

Sande, Mark Carson For effective coastal management it is important to understand how sea levels will change locally in

the future. Changes to mean sea level and sea level extremes (e.g., storm surges) will lead to changes

in coastal impacts. Preparedness is normally based on return levels from statistics of the water levels

in the observed record. With changing mean sea levels due to climatic change and land uplift return


Palma de Mallorca, June 10-12, 2015 levels will change accordingly. The goal of this work is to provide projections of future return levels

for each coastal municipality in Norway.

We first perform an extensive and comparative analysis of observed sea level from tide gauges and

altimetry, in order to assess the current rates and natural variability. State of the art land uplift rates

for the coastal municipalities are determined assessing new GPS observations as well as GIA

modelling.

Our regional sea level projections are based on findings from the Fifth Assessment Report (AR5) of

the Intergovernmental Panel for Climate Change (IPCC), and the Coupled Model Intercomparison

Project phase 5 (CMIP5) output, but using our own land uplift rates and corresponding gravitational

effects on sea level, as well as estimates of self attraction and loading. The average projected 21st

century relative sea level change in Norway is -0.10–0.35 m (90% uncertainty bounds) for RCP2.6,

0.00–0.45 m for RCP4.5, and 0.10–0.65 m for RCP8.5. However, the relative sea level projections can

differ as much as 0.50 m from place to place, mostly governed by the land uplift pattern.

Further, the extreme value analysis and return levels for Norway have been reassessed, and together

with the sea level projections applied to a modified version of Hunter’s method. We thus provide

estimates for how much assets need to be raised so that the probability of flooding remains

preserved.

Sea surface height variability in the North East Atlantic from satellite altimetry. Paul Sterlini,

Hylke de Vries and Caroline Katsman Sea surface height variability (SSV) operates in varying temporal and spatial scales and acts as a

source of noise when trying to perform long term trend analysis on the sea surface height (SSH). This

study seeks to identify (and ultimately remove) the major contributing components of the SSV in the

North-East Atlantic to expose the underlying changes in the SSH signal. This allows a trend analysis

on the "cleaned" SSH for an accurate determination of sea level rise.

Observations of sea level anomalies are taken from 21 years of satellite altimeter data and are used

to estimate the SSV in the North-East Atlantic. Seasonal signals are removed and monthly means

calculated. The SSV is decomposed into global, regional and local components and a simple multiple

linear regression model is constructed on the basis of these components to model the explained SSV.

Initial results show that a region of high SSV exists off the west coast of Denmark and can be well

represented with a regression model which uses local wind and global temperature as primary

regressors. This work will help in understanding regional sea level change over the past 21 years and

to provide a foundation for estimates of local sea level change in the near future.

What is the most robust time series analysis tool to isolate mean sea level from tide gauge

records?. Phil Watson One of the most critical environmental issues confronting mankind into the foreseeable future

remains the ominous spectre of climate change, in particular the pace at which impacts will occur

and our capacity to adapt. Sea level rise is one of the key artefacts of climate change that will have

profound impacts on global coastal populations. Although extensive research has been undertaken


Palma de Mallorca, June 10-12, 2015 into this issue, there remains considerable conjecture and scientific debate about the temporal

changes in mean sea level and the climatic and associated physical forcings responsible for them. In

particular, over recent years, significant debate has centred around the issue of a measurable

acceleration in mean sea level, a feature central to projections based on the current knowledge of

climate science. The complexity of the dynamic influences and noise embedded within ocean water

level data sets has led sea level research toward successively more sophisticated time series

techniques to estimate the trend. In the absence of an absolute knowledge of the mean sea level

signal (or trend) for a particular record, the accuracy of the trend has increasingly been inferred from

the assumed sophistication of the applied analytic. An innovative and transparent process by which

to identify the most efficient technique for isolating the mean sea level signal is to test such

approaches against “synthetic” (or custom built) data sets with a known mean sea level signal. This

paper details the development of a comprehensive monthly average data set comprising 20,000 time

series to meet the above-mentioned objective. The paper also presents the results of the detailed

testing using an extensive array of time series techniques to reveal the most statistically robust

analytic for isolating mean sea level from conventional ocean water level records with improved

temporal resolution.

Regional evaluation of surface mass balance forcing of an ice flow model for the Greenland Ice

Sheet using GRACE mascon solutions. D. N. Wiese, N.-J. Schlegel, M. M. Watkins, E. Y. Larour, J.

E. Box, X. Fettweis, M. R. van den Broeke Quantifying Greenland's future contribution to sea level rise is a challenging task and requires

accurate estimates of ice flow sensitivity to changing climates. Transient ice flow models are

promising tools for estimating future ice sheet behavior; however, confidence in these types of

projections is low due to a scarcity of data for validation of model historical runs. For more than a

decade, the Gravity Recovery and Climate Experiment (GRACE) has continuously acquired time-

variable measurements of the Earth's gravity field and has provided unprecedented surveillance of

mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we

take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass

balance comparison with an independent, historical ice flow model simulation using the Ice Sheet

System Model (ISSM). The comparison highlights which regions of the ice sheet model differ most

from GRACE observations. Investigation of regional differences in trends and seasonal amplitudes

between simulations forced with different Regional Climate Model (RCM)-based estimates of surface

mass balance (SMB) allows us to make conclusions about the relative contributions of errors in both

models of SMB and ice dynamics. We highlight the importance of utilizing an ice flow model for

future projections rather than relying solely on projecting future changes in SMB. This study

constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid

in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and

future rates of sea level rise.

A review of trend models applied to sea level data with reference to the “acceleration-

deceleration debate“. H. Visser, S. Dangendorf, A.C. Petersen Global sea levels have been rising through the past century and are projected to rise at an

accelerated rate throughout the 21st century. This has motivated a number of authors to search for


Palma de Mallorca, June 10-12, 2015 already existing accelerations in observations, which would be, if present, vital for coastal protection

planning purposes. However, no scientific consensus has been reached yet how to separate a

possible acceleration from intrinsic climate variability in sea level records. This has led to an intensive

debate on its existence and, if absent, also on the general validity of current future projections.

Here we shed light on the controversial discussion from a methodological point of view. We provide

a comprehensive review of trend methods used in the community so far. This resulted in an overview

of 30 different methods, each having its individual mathematical formulation and flexibilities. We

discuss various pros and cons of these methods and illustrate that varying trend approaches may

lead to contradictory acceleration–deceleration inferences. We argue that model selection

techniques and good modeling practices in combination with a comprehensive understanding of sea

level dynamics yield a way-out here. In particular, we conclude that (i) several differently

characterized methods should be applied and discussed simultaneously, (ii) uncertainties provided as

confidence bounds should be taken into account to prevent biased or wrong conclusions, and (iii)

removing internally generated climate variability by incorporating atmospheric or oceanographic

information helps to uncover externally forced climate change signals.

Sea Level Extremes

Oral Presentations

Nineteenth Century Sea-level and Extremes on the US East and West Coast. Stefan Talke, David

Jay, Patrick Lau, Conrad Hilley, Lumas Helaire, Drew Mahedy, Ramin Familkhalili Continuous tidal measurements began in 1844 and 1853 on the East and West coast of the United

States, but only a small portion of these data have been analyzed for sea-level rise and extreme

events. In this presentation we describe the progress of efforts to recover and digitize more than

200 station-years of 19th and early 20th century data from Boston (MA), Sandy Hook (NJ), Charleston

(SC), Norfolk (VA), Wilmington (SC), San Diego (CA), Astoria (OR), Port Townsend (WA), Sitka (AK) and

Kodiak (AK). Over 50,000 pictures have been taken at the US National Archives and local archives,

and more than 1 million data points digitized by students. Approximately 15 years of tide-charts

(marigrams) from Astoria, OR (1853-1876) have been digitized at 1 minute resolution using a

software-based line recognition program we developed. Traditional harmonic analysis, spectral

analysis, and wavelet-based tidal analysis are used to quality assure data and identify periods of

anomalous (bad) data. The role of hydrodynamic gradients on sea-level collected at different station

locations will be assessed, and the challenges of connecting historical sea-level to a modern datum in

tectonically active regions will be discussed. Preliminary results suggest that the 19th century data is

valuable for assessing long-term trends in sea-level, sea-level acceleration, and extremes. Results

suggest that the once-in-10 year storm tide in New York City has increased by nearly 0.3m since the

1850s. Preliminary results also suggest that tidal range in Wilmington (NC) has doubled since 1887,

leading to a more than 1m increase in the worst-case scenario storm surge (a category 5 hurricane).

Hence, 19th century data provide insights into trends in the total water spectrum and can help local

efforts to adapt to climate change.



Storm surge clustering and spatial footprints: How extreme was the 2013-2014 UK storm surge

season? Ivan D. Haigh, Matthew P. Wadey, Shari L. Gallop, Robert J. Nicholls Coastal flooding can be devastating, with long-lasting and diverse consequences. The UK has a long

history of severe coastal flooding. The continued threat of serious flooding was apparent during

winter 2013–2014 when the UK experienced a series of storm surge events. What is noteworthy

about the 2013-14 winter period is the: (1) large number of exceptional high waters and coastal

floods over a relatively short time period; and (2) the large number of coastal regions affected.

Extreme events are rarely assessed in terms of temporal ‘clustering’, despite the fact that ‘repeated

shocks’ to defences and communities can reduce time for recovery and lead to amplified flood

damages. The spatial dependence or ‘footprint’ of flood hazards is also receiving more attention,

motivated by concern from re-insurance, infrastructure reliability and emergency response.

Here we assess how unusual the 2013-14 storm surge season was in the last 100 years, in terms of

both temporal ‘clustering’, and the spatial ‘footprint’ of events. To do this we analyse sea level

records at the UK’s national tide gauge sites, and use a threshold of the 1 in 5 year return period to

select high waters that are potentially relevant to flooding. Using meteorological re-analysis data, we

determine storms tracks and characteristics that generated these extreme sea level events. In total,

we identify 96 events that generated water levels greater than the (1 in 5 year return period)

threshold. For each event, the time to the next nearest event is calculated and the spatial footprint

estimated. This is compared for all years on record. Finally, we consider how to improve estimates of

extreme sea levels using advanced statistical methods that can represent event clustering and

footprints; in order to provide stakeholders with tools to improve how coastal flood risk is identified,

assessed and planned for.

Regional climate variability in extreme sea levels from satellite altimetry observations over two

decades. Melisa Menendez, Philip L. Woodworth The patterns of variability and change in extreme sea levels are of particular interest for both

scientific and practical reasons. Observations from tide gauge records are the main source of sea

level information at the coast, however, for deep ocean and some coastal areas no or only very short

and incomplete measurements exit.

Sea surface height from satellite altimetry provide sea level variability info over the last two decades.

This study analyzed a inter-calibrated satellite altimetry data set of Topex/Poseidon, Jason and

OSTM/Jason2 missions from 1993 to 2012.

A global analysis if extreme sea level is made by aggregating individual measurements into grid boxes

with approximately two values per day. The parameters of the Generalised Extreme Value

Distribution describes the behavior of the most unusual extreme events. Location and scale

parameters presents the types of variability associated primarily with fluctuations in the ocean

circulation. Positive shape parameter values include the eastern tropical Pacific, northern

extratropical coastal areas in the western Pacific and Atlantic Oceans, a band across the Aleutian

Islands and at high latitudes.


Palma de Mallorca, June 10-12, 2015 The seasonal fluctuations, interannual variability and trends are also investigated by using a time-

dependent extreme model. The influence of the Arctic Oscillation (AO), North Atlantic Oscillation

(NAO), El Niño south oscillation (Niño 3 index), and Southern Annular Mode (SAM) on extreme sea

levels is assessed by introducing the climate indices as covariates into the model. Finally, regional

positive linear trends in extreme sea levels are determined largely by the corresponding spatial

variations in mean sea level changes worldwide.

Time varying trends in sea level extremes. Marta Marcos, Francisco M. Calafat, Angel Berihuete,

Sönke Dangendorf While there is scientific consensus on mean sea level rise during the last century at both global and

regional scales, changes in extreme sea levels are more uncertain. Accurate assessments of the

likelihood of extreme events are essential to i) describe the temporal variability in extreme frequency

and intensity and quantify its probability of occurrence, ii) understand the processes that drive

extreme sea level events and iii) plan and adopt strategies for coastal management. Here we use

state space models to evaluate non-stationary changes in extreme sea levels and derive time-varying

return periods. We have used a set of long (>50 years) coastal tide gauges with hourly sampling

worldwide distributed and we seek for regional and temporal consistency in the observed changes in

sea level extremes

Cyclone Xaver seen by Geodetic Observations. Leonor Mendoza, Luciana Fenoglio-Marc, Remko

Scharroo, Alessandro Annunziato, Matthias Becker, John Lillibridge Cyclone Xaver pounded the North Sea on 5-6 December 2013 and reached its maximum in the

German Bight the second day. The radar altimeter on-board the SARAL/AltiKa satellite measured the

largest storm surge signal captured by satellite altimetry to date, nearly 3 m, at the maximum. A local

dense network of in-situ stations (tide gauges and GPS) monitored the event over several days. The

combined geodetic measurements detect alongshore and cross-shelf surge variations and land

subsidence.

The GPS network detects a maximum land subsidence at the GPS locations of 4-6 cm, in excellent

agreement with the loading of the predicted surge by two forecast models in both measure and

occurrence. The differences between the surge model predictions at the peak event are mainly

caused by different wind forcing and reduce from 1 to 0.3 meters when the same wind forcing is

used in both models.

Observations largely agree with model predictions on wind speed (Root-Mean-Square (RMS) of the

differences is 4 m/s) and surge height (RMS 30 cm) and mostly differ on wave height (RMS 2 m).

The temporal and spatial characteristics of the surge and vertical displacement derived from the

observations along the coast agree with the simulations. The water height indicates both a direct

large scale forcing and a shelf wave dynamics with anticlockwise propagation of the surge. Instead,

the temporal and spatial evolution of the vertical displacement appears to be mainly affected by this

last component. After post-processing, the 1-minute sampling GPS time series monitor very well the

propagation direction of the storm; the maximum subsidence is reached in the stations following the


Palma de Mallorca, June 10-12, 2015 anticlockwise path of the surge. The along-track off-shore observations provided by satellite

altimetry are valuable information to validate the simulations off-shore.

The results underline the importance of geodetic measurements in improving existing forecast

approaches.

Future storm surge levels - the example of Denmark. Kristine S. Madsen, Torben Schmith, Tian

Tian Sea level rise will be one of the dominating effects of global warming, and one of the main impacts

will be on storm surges. Here we assess the changing wind contribution on future storm surges in the

North Sea – Baltic Sea region and combine it with mean sea level rise projections from the latest IPCC

report and from regional studies, in preparation for dedicated hydrodynamic simulations including

both. We will discuss the impact of land rise and changing tides. The changes in extreme sea level

due to wind has been assessed by dynamically downscaling GCM results using a regional atmospheric

climate model and the same hydrodynamic ocean model as is used for operational storm surge

modelling in Denmark. The assessment shows possibilities for increased storm surge contributions of

up to 0.3 m on exposed coasts of the North Sea and the Baltic Sea, whereas no significant changes

are seen along more sheltered coastlines. This increase must be combined with changes of the mean

sea level. The observed sea level rise in Denmark, when corrected for land rise, lies very close to the

global mean value of the last century. For the future, the IPCC AR5 projections of mean sea level rise

of the North Sea - Baltic Sea area from 1986-2005 to 2081-2100 range from 0.3 m to 0.6 m for the

four RCPs, with and standard deviation of approximately 0.3 m. The IPCC report does not give an

upper range for risk assessments, but DMI has, in corporation with University of Copenhagen,

estimated and upper limit for a medium-high climate scenario for Denmark to be 1.4 m by year 2100.

Today, a storm surge of 1.5 m is a 100-year event in Copenhagen. With a sea level rise of 0.5 cm, this

level will be reached every second year.

Meteorological Tsunamis In The World Oceans: An Overview. Alexander Rabinovich “Meteorological tsunamis” (or “meteotsunamis”) are destructive tsunami-like waves that have

approximately the same temporal and spatial scales as ordinary tsunami waves and can affect coastal

areas of the ocean in a similar devastating way. In particular regions and in certain situations,

meteotsunamis can have catastrophic effects and even lead to death. Meteotsunamis are generated

by various types of atmospheric disturbances, including trains of atmospheric gravity waves, passing

fronts, squall lines, and jumps in atmospheric pressure.It is common for strong meteotsunamis to be

associated not with some extreme events, like typhoons and and hurricanes, but with calm weather

associated with high-pressure systems. There are some specific regions where meteotsunamis are

regularly observed: the Balearic Islands, Spain; west coasts of Sicily, Italy and the Adriatic Sea,

Croatia; Kyushu Island, Japan; Longkou Harbour, China, and the Great Lakes, USA-Canada.

Meteotsunamis have a resonant mechanism of generation and cited particular regions have

favourable conditions for their formation. However, considerable interest in the tsunami problem, in

general, initiated by the catastrophic 2004 Sumatra and 2011 Tohoku tsunamis, and by significant

improvement in instrumentation (high-precision tide gauges and microbarographs) recording these

events, has recently led to new information on meteorological tsunamis and demonstrated that this

is a much more common and widespread phenomenon than had been considered previously. Major


Palma de Mallorca, June 10-12, 2015 meteotsunamis in 2013-2014 occurred on the East Coast of the USA, in Brazil, in the Gulf of Mexico,

in Australia and the Mediterranean. All of these events were well documented and are under

thorough investigation. The key scientific and applied question is the elaboration of effective and

reliable methods of meteotsunami forecasting.

The impact of sea level rise on storm surge water levels and wind waves. Arne Arns, Jürgen

Jensen The impact of sea level rise on extreme water levels and wind waves is investigated using a numerical

model that covers the entire North Sea, but has its highest spatial resolution in the northern part of

the German Bight. A 40-year hindcast covering the period 1970 to 2009 is conducted using observed

mean sea level changes, tides and atmospheric forcing as boundary conditions. The model

reproduces the observed water levels and wind waves well for this control period. A second 40-year

run is then conducted considering the same atmospheric forcing but adding +0.54 m to the MSL to

explore the effects of sea level rise on storm surges and wind waves in the investigation area.

At most locations, the second model run leads to changes in the storm surge water levels that are

significantly different from the changes in MSL alone. The largest increases of the order of 15 cm (in

addition to the MSL changes) occur in the shallow water areas of the Wadden Sea. These increases

are caused by nonlinear changes in the tidal constituents which, however, are spatially not coherent.

Also the wave heights show significant increases which are mainly caused by the larger water depth

reducing the association between storm surge water levels and depth limited wave heights.

Finally, we estimate the impact of SLR on return water levels using extreme value analyses. Our

analyses highlight that this impact is nonlinear and spatially incoherent. In some locations, the

increase in return water levels is nearly constant for all exceedance probabilities with values

exceeding the considered SLR by 7-10 cm. Together with the simulated changes in wind waves,

required increases in design levels (considering water levels and wind waves or wave run-up) are

expected to be considerably above the rate of SLR alone. For instance, to keep the current safety

levels, coastal defenses need to be improved by up to twice the considered SLR locally.

Atmospheric Circulation Changes and their Impact on Extreme Sea Levels and Coastal Currents

in Australia. Kathleen L. McInnes, Frank Colberg, Julian O’Grady Extreme sea levels are a significant hazard for many low-lying coastal communities, causing a range

of coastal impacts such as flooding and erosion. Changes in atmospheric circulation patterns and

severe weather systems may therefore lead to changes in the frequency and intensity of extreme sea

levels and the strength of coastal currents. In this study a hydrodynamic model at 5 km resolution

has been implemented over Australia to investigate future changes to sea levels and currents. The

role of tide-surge interaction is first assessed and found to have negligible effects on storm surge

heights over most of the coastline. Tidal forcing is therefore omitted in the climate change

simulations. Twenty-year simulations are carried out over the time periods 1981-1999 and 2081-

2099 using atmospheric forcing from four CMIP5 climate models. Results suggest that extreme sea

levels will undergo small changes along much of the Australian coastline. However there are some

regions along the north and south coasts of mainland Australia that appear to be sensitive to


Palma de Mallorca, June 10-12, 2015 projected changes in circulation patterns, particularly in the Austral summer months. These changes

and their possible coastal impacts will be presented and discussed.

Global Secular Changes in different Tidal High Water, Low Water and Range levels. Robert J.

Mawdsley, Ivan D. Haigh,N.C. Wells Tides exert a major control on the coastal zone by influencing high sea levels and coastal flooding,

navigation, sediment dynamics and ecology. Therefore, any changes to tides have wide ranging and

important implications. In this paper, we uniquely assess secular changes in 15 regularly used tidal

levels (five high water, five low water and five tidal ranges), which have direct practical applications.

Using sea level data from 220 tide gauge sites, we found changes have occurred in all analysed tidal

levels in many parts of the world. For the tidal levels assessed, between 36% and 63% of sites had

trends significantly different (at 95% confidence level) from zero. At certain locations, the magnitude

of the trends in tidal levels were similar to trends in mean sea level over the last century, with

observed changes in tidal range and high water levels of over 5mm/yr and 2mm/yr respectively.

More positive than negative trends were observed in tidal ranges and high water levels, and vice

versa for low water levels. However we found no significant correlation between trends in mean sea

level and any tidal levels. Spatially coherent trends were observed in some regions, including the

north-east Pacific, German Bight and Australasia, and we also found that differences in trends occur

between different tidal levels. This implies that analysing different tidal levels is important. Because

changes in the tide are widespread and of similar magnitude to mean sea level rise at a number sites,

changes in tides should be considered in coastal risk assessments.

Posters

How to interpret expert judgment assessments of 21st century sea-level rise? Hylke de Vries,

Roderik S.W. van de Wal Over the last years it has been realized that the ice dynamical contribution of ice sheet to sea level

can possibly not be estimated in a deterministic way. As a result a few expert assessments have

attempted to estimate sea-level rise. It turned out that experts have a strongly diverging opinion on

the ice sheet contribution. We argue that such lack of consensus should form an essential and

integral part of the subsequent analysis of the data. By employing a method that keeps the level of

consensus included, and that is also more robust to outliers and less dependent on the choice of the

underlying distributions, we obtain on the basis of the same data lower high-end estimates. We show

that results are sensitive to assumptions on the shape and minimum of the underlying distributions.

Our analysis therefore demonstrates that one should be careful in considering high-end sea-level rise

estimates as being well-determined and fixed numbers.



Expected Vertical Load in coastal GPS due to a Tsunami like the 1775 Lisbon Tsunami: GPS

Tsunami Early-Warning capabilities. Leonor Mendoza An approach for tsunami early warning is studied, based on GPS observations of the vertical crustal

loading caused by a tsunami-induced redistribution of water.

The test area is the Atlantic coast of the Iberian Peninsula. Due to the lack of real tsunami recordings

in the region, this approach could not be tested using data recorded in-situ. Instead, the GPS

sensitivity and detection capability has been evaluated for coastal stations in the Iberian Peninsula

during two periods of extremely high tides in 2011. GPS measurements have been compared to

vertical displacement caused by the predicted and observed water levels. GPS data corrected for the

predicted ocean tidal loading does not show any signal above noise level in those periods.

Moreover, two tsunami models (best- and worst-case scenarios) have been used to estimate the

crustal vertical deformation due to a tsunami with similar characteristics of the 1755 Lisbon tsunami.

Arrival times of the maximum subsidence and water height have been compared in order to establish

the possible warning time available for each scenario. This accommodation time is fundamental for

the early warning of an incoming tsunami, because the subsidence experienced and the amount of

water traveling toward the coast are intrinsically linked.

Analysis of recent high-frequency sea level events in the European Atlantic coast: impact on the

design of automatic algorithms for tsunami detection. Begoña Pérez Gómez, Marta Gómez

Lahoz, Enrique Álvarez Fanjul, Carlos González, François Schindele The upgrade of the sea level networks worldwide, to allow their integration in the sea level related

hazards warning systems, have increased significantly our possibilities of measuring and analysing

high frequency sea level oscillations. Many tide gauges around the European waters provide today 1’

(or less) sea level data which reveal the common occurrence of such events, with periods of several

minutes. Their origin and spatial distribution is diverse and must be better understood, for a correct

design and interpretation of the automatic detection algorithms to be used by the tsunami warning

centers in the region. We will present here the analysis of two events recorded in the European

Atlantic coast: the wave induced “seiches” occurred along the North of Spain during the storms of

January and February of 2014, and the potential detection of a small tsunami after an earthquake in

the midle of the Atlantic the 13th of February of 2015. The former caused significant floods in towns

and villages and an stunning increase of the waves induced coastal damage that was present in the

media during weeks. The second, however, was just a small signal present in several tide gauges in

the Atlantic coast that, although fortunately unnoticed by the local population, could yield significant

information for tsunami wave modellers and the development of tsunami detection software. In

both cases the REDMAR tide gauges from Puertos del Estado did send automatic messages to the

network operators, that revealed the importance and relatively well performance of the automatic

detection algorithms developed for this network. This study will provide, therefore, not only the

physical description of the two mentioned events but, at the same time, a better understanding of

the limitations of this type of automatic algorithms and the possible improvements on the

information provided to the tsunami warning centers in order to distinguish clearly both types of

signals.



Estimation extreme sea levels from the combination of tides and storm surges for the coasts of

the Sea of Okhotsk. Georgy Shevchenko Extreme sea levels arising from the combination of tides, seasonal and meteorologically-induced

oscillations (including the extreme events, storm surges) were estimated by the joint probability

method for the coast of the Sea of Okhotsk and the Pacific coast of the Kuril Islands. The sea level

observations at 10 coastal tide gauges (6 stations on the Kuril Islands, 3 on the eastern coast of

Sakhalin Island and 1 on the northern coast of the Sea of Okhotsk) were examined. High quality 1-

year time series of hourly sea level data were used for harmonic tidal analysis. The tidal heights at

most stations are about 1.5 - 2 m, and only at Magadan they are much larger (about 5 m). Storm

surges have the largest heights for the central Kuril Islands (Matua and Iturup islands), while at the

North and South Kuril Islands the surge heights are the smallest. The winter maximum in sea level is a

specific feature of seasonal variations in this region which is associated with the winter amplification

of cyclonic circulation over the Sea of Okhotsk and with the prevailing winds. The monthly mean sea

level series were used to compute the amplitudes and phases of annual (Sa) and semiannual (Ssa)

seasonal constituents. The mean values of seasonal harmonics were used to calculate the probability

density functions (PDF) in combination with tides. Predicted time series for the 19-years interval (we

used 2000-2018 to take into account the 18.6 years tidal nodal cycle) were used to calculate the PDF

(histogram) with class interval 5 cm. The residual series (after subtracting tides and seasonal

variations) were used to analyze meteorologically-induced sea levels and storm surges, and to

calculate their PDF (histogram of total residual series). Storm surges have the largest heights for the

central Kuril Islands (Matua and Iturup) islands.

Spatial variation in extreme water levels in the Baltic Sea – North Sea transition from tide gauge

records. Carlo Sørensen, Ole B. Andersen, Per Knudsen Extreme water levels in the Baltic Sea – North Sea transition are governed by a variety of factors (met

forcing, nearshore bathymetry and profile slopes, coastline orientation, water compartment

configuration, fiord sills etc) that provide a complex picture between locations. Currently about 70

tide gauges (TG), with data series ranging from less than 20 to 125 years (21 TG 60y), are deployed

along the 7,300 long and diverse Danish coastline (in addition to these are Swedish, Norwegian and

German TGs). Unfortunately, many of the long data series have not been digitized (pre-1970s) and

where only the extremes have been extracted in the past. Some full series are available e.g. for

digitization, whereas others are deemed to have been lost. Furthermore, data quality is varying. Still,

in toto, TGs provide a unique background data set for EVA on water levels. In an on-going study, we

research the spatial variation and regionalization in order to provide more objective and robust

statistics. This includes among other detrending, choice of distribution functions (building on the

work of Arns et al, 2013), and possible ways of including historical events of an assumed very low

probability. The paper outlines the methodological approach, presents results from selected water

compartments and the work ahead, as well as some core issues of validation of TG series and

statistics (not often addressed; e.g. temporal coherence and TG’s ability to actually measure the

“true” extremes) are highlighted to discuss these matters with the scientific community at the

workshop.



The Impact of an Eroding Barrier Island on Extreme Water Levels in the Tampa Bay Area. Marius

Ulm, Arne Arns, Jürgen Jensen Barrier islands characterize an eighth of the global coastlines. Since barrier islands are part of a

dynamic coastal regime, a change in their shape or even a complete erosion may lead to an increased

impact of storm surge events on the mainland. A barrier island which is under the particular threat of

erosion is Egmont Key, located in the mouth of the Tampa Bay estuary in Florida.

For the investigation of the influence of barrier islands on storm surge water levels at the mainland’s

coast, two 2D depth averaged hydrodynamic-numerical models of the Gulf of Mexico and of the

adjacent Tampa Bay were set up using Delft3D. The models were forced with tidal and

meteorological information using inputs from a global tide model and reanalysis data. In a first step,

a 63 year water level hindcast (A-scenario) for the period 1948-2010 in combination with a

parametric bias correction derived from a fit against existing tide gauge observations was developed.

In a second step, this run was repeated using the same boundary conditions as in the A-scenario but

with Egmont Key removed from the bathymetry (B-scenario). In a third step, the bias-corrected

water levels from the A-scenario, as well as the water level increases from the B-scenario added up

on the corrected A-scenario water levels were used to estimate return water levels. The return level

assessment was conducted using the peaks over threshold method based on the 99.8th percentile

threshold exceedances.

The A-B comparison of the return water levels along the coastline of the Tampa Bay shows that

Egmont Key has a significant influence on the mainland, especially in the northern parts of the

estuary. An increase in the order of 5 cm to 17 cm for a return period of 100 years indicates that the

barrier island Egmont Key provides natural coastal protection for the mainland. Furthermore, a small

increase in the tidal range and a 20 minute time shift in the peak time series imply that the flushing

of the estuary would also be affected by a potential disappearance of Egmont Key.

Coastal Impacts of Sea Level Changes

Oral Presentations

Evaluating uncertainties in future coastal flooding occurrence as sea-level rises. Gonéri Le

Cozannet, Jeremy Rohmer, Anny Cazenave, Déborah Idiera, Roderik Van de Wal, Renske de

Winter, Rodrigo Pedreros, Yann Balouin, Charlotte Vinchon, Carlos Oliveros As sea-level rises, the frequency of coastal marine flooding events is changing. For accurate

assessments, several other factors must be considered as well, such as the variability of sea-level rise

and storm surge patterns. Here, a global sensitivity analysis is used to provide quantitative insight

into the relative importance of contributing uncertainties over the coming decades. The method is

applied on an urban low-lying coastal site located in the northwestern Mediterranean, where the

yearly probability of damaging flooding could grow drastically after 2050. Storm surge propagation

processes, then sea-level variability, and, later, global sea-level rise scenarios become successively

important source of uncertainties over the 21st century. This defines research priorities that depend


Palma de Mallorca, June 10-12, 2015 on the target period of interest. On the long term, scenarios RCP 6.0 and 8.0 challenge local

capacities of adaptation for the considered site.

Effects of scale and input data on assessing the future impacts of coastal flooding. An

application of DIVA for the Emilia-Romagna coast. Claudia Wolff, Athanasios T. Vafeidis, Daniel

Lincke, Christian Marasmi, Jochen Hinkel Coastal flood impacts under 21st century sea-level rise are assessed for Emilia-Romagna (Italy) using

the Dynamic Interactive Vulnerability Assessment (DIVA) modeling framework. The sensitivity of the

modeling tool to three parameters, namely (1) elevation, (2) population and (3) vertical land

movement as well as (4) to the scale of assessment are investigated. A one-driver-at-a-time

sensitivity approach was used in order to explore and quantify possible errors and uncertainties in

input data and assessment scale on model outputs. Our results show that coastal flood impacts by

the end of the century are more sensitive to variations in elevation and vertical land movement input

data than to variations in population. The inclusion of human induced subsidence rates increases the

relative sea-level by 55cm in 2100. This leads to up to two times higher coastal flood impacts

compared to those generated with the global DIVA values, which only account for natural processes.

Furthermore, the choice of one elevation model over another can result to differences of around

60% in the extent of the coastal floodplain area and up to 70% in flood damages in 2100. These

model results indicate that variations in vertical land movement and elevation data can be very

significant to the calculation of coastal flood impacts.

The change in assessment scale was implemented via the use of a more detailed coastline and input

data (e.g. higher resolution) for the coastline segmentation process. This lead to an increase in the

number of coastal segments and a 28-fold decrease of average length per segment. Model results

show a moderate sensitivity to this change Nevertheless, we observed that the more detailed

assessment scale resulted in a more realistic spatial representation of coastal flood impacts for the

Emilia-Romagna coast. The results emphasize that different input datasets and assessment scales

have different uncertainties and implications on the results of coastal flood impact assessments.

Therefore, it is important to investigate and communicate those uncertainties in order to effectively

support decision-makers as there is a growing need to continue planning for the future, even if

future projections are not robust.

An assessment of extreme sea levels, waves and coastal flooding in the Maldives. Matthew

Wadey, Ivan Haigh, Sally Brown, Robert Nicholls As part of a project that aims to assess impacts and vulnerability of coastal systems (at local, regional

and global scales) to sea level rise (SLR) we provide a case study of the low-lying Island nation of the

Maldives. The Maldives are regarded to imminently face the detrimental effects of SLR. We focus

upon the man-made island of Hulhumalè (adjacent to the capital, Malé) which is undergoing rapid

population growth. Our aim is to assess coastal inundation scenarios to inform practical options for

adaptation. The first objective is to assemble data on extreme sea levels, waves, past events and

defences, which includes analysis of tide gauge records and floodplain elevation maps. The second

objective is to model defence failures and inundation across a range of 21st century mean SLR

projections and extreme storm events. This includes coupling the output of a numerical wave


Palma de Mallorca, June 10-12, 2015 overtopping model to flood spreading simulations. By showing land and property affected, we

analyse these inundation scenarios in context with present-day and future coastal flooding events,

and discuss adaptation pathways.

Land subsidence and sea level rise at Lipari island (Italy): implications for flooding scenario.

Anzidei Marco, Bosman Alessandro, Carluccio Roberto, Carmisciano Cosmo, Casalbore Daniele,

Chiappini Massimo, Chiocci Francesco Latino, D’Ajello Caracciolo Francesca, Esposito

Alessandra, Fabris Massimo, Muccini Filippo, Nicolosi Iacopo, Pietrantonio Grazia, Sepe

Vincenzo, Vecchio Antonio The volcanic Island of Lipari is located in the active volcanic arc of the Aeolian islands, between the

Southern Tyrrhenian Sea back arc basin (Marsili basin) and the Calabrian Arc, an orogenic belt

affected by a Late Quaternary extensional tectonics and uplift.

In this geodynamic framework, continuous and episodic GPS data collected at Lipari and nearby

islands in the time span 1996-2012, evidenced an active crustal deformations. Particularly, the

vertical component of land motion is causing the rapid subsidence of Lipari at velocities even

exceeding 10 mm/yr. Instrumental data are in agreement with independent local observations based

on archaeological data, that show a continuous subsidence with rates at about 8 mm/yr since the last

2000 years B.P.

On these basis, an integrated study of this area was planned. Multibeam bathymetry with aerial

digital photogrammetry, the latter also performed locally by drone surveys, were combined to

generate a ultra-high resolution digital terrain model of land and submarine areas. The latter was

extracted with a resolution up to 0.1 m, thus supporting the creation of a detailed flooding scenario

for 2100, based on the sea level rise projections estimated from the analysis of tide gauge data

collected in the central Mediterranean in the time span 1872-2014 and IPCC reports.

Finally, relative sea level rise at Lipari is expected to cause large impacts on the environment and the

coastal installations, representing a significant hazard factor for the local population living near the

shore

Posters

Characterization and Hybrid Downscaling of Wave Climate at a central Pacific atoll for extreme

sea level impacts assessment in Funafuti, Tuvalu. Ron Hoeke, Kathleen McInnes, Tom Durrant Quantitative knowledge of nearshore wind-wave climate is essential for effective coastal

management. This is particularly the case for steep-shelfed islands where waves are the dominant

cause of extreme sea levels and coastal inundation (Hoeke et al, 2012). Information needs are

particularly pertinent in atoll nations, which are perceived as highly vulnerable to sea level rise.

Robust simulations of wave climate are increasingly available, however the spatial scales and bulk

statistics of available (stored) output are ineffective for many coastal applications. Here, we

characterize the complex deep-water wave climate of Tuvalu through partition analysis of deep-

water wave spectra from a global hindcast simulation and implement a high resolution unstructured


Palma de Mallorca, June 10-12, 2015 wave model to simulate the complex wave propagation and dissipation patterns around the atoll.

The deep-water wave climate and high resolution model are then used to downscale wave climate

for the entire atoll through a hybrid statistical/dynamical approach. The results show how the atoll's

morphology acts as a complex filter to deep-water wave climate: different areas on both the seaward

sides and within lagoon are subjected to very different modal and episodic (extreme) neashore wave

regimes associated with different meteorological conditions and (swell) source regions. The

complexities of both local wave climate and atoll morphology provided a challenging test bed for the

hybrid downscaling methods we developed in this study. Therefore the successful application of the

methods to this study site suggest they will be readily applicable to most other coastal regions to

provide greatly improved quantification of local wave climate on scales pertinent to coastal

engineering and management.

Simulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea

level rise effects. Sylvestre Le Roy, Rodrigo Pedreros, Camille André, François Paris, Sophie

Lecacheux, Fabien Marche, Charlotte Vinchon Recent progresses in numerical modelling and data acquisition have allowed significant

improvements in coastal flooding simulations, with a maturity of numerical tools that now allows

very precise results in urban areas. Essentially used for hazard studies, their reliability now offers the

perspective to estimate the impact of sea level rise on coastal flooding hazards.

The presented method is based on simultaneous simulation of wave overtopping and resulting flood

in urban areas. This type of two-dimensional simulations can afford reproducing both the chronology

and the effect of urban areas on flood dynamics. The method consists in elaborating, from larger

simulations, a time-series of instantaneous water levels, including waves. This time-series is imposed

upon a time-dependent phase-resolving model to simulate dynamically wave overtopping and the

resulting flood, using a Digital Elevation Model that includes buildings.

This method has been applied to the Johanna storm (2008) in Gâvres (France). SURF-WB, a NLSW

model, allowed simulating both overtopping dynamics and flooding, taking into account buildings

thanks to a 1m-resolution. Obtained results proved to be very consistent with available reports

(overtopping sectors, flooded area, water heights and chronology). This method allows reproducing

very realistically overtopping and flooding dynamics in an urban area (water heights and velocities),

with an increased accuracy and very realistic results compared to more classical approaches.

This type of simulations can be used to estimate the potential evolutions of coastal flooding

processes in a context of sea level rise due to climate change, supposing nevertheless a non-modified

morphology. Preliminary simulations realized on the site of Gâvres showed how sea level rise could

increase overtopping for a storm like Johanna. For example, a rise of 20 cm of the sea water level

may lead to a slightly larger flooded area, but with water heights increasing of about 28 cm, due to

the modifications in overtopping flows and chronology.



Tidal influence on high frequency harbor oscillations in a narrow entrance bay. S.

Monserrat, I. Fine, A. Amores, M. Marcos High frequency sea level oscillations at Wells Harbor (Maine, Northeastern US), with periods in the

range of several tens of minutes, display a tidally modulated response. During low tides these sea

level oscillations reach amplitudes of 10-20 cm, while during high tides they are significantly smaller.

Wells Harbor is located in a low lying area with a tidal range of about 2 m and is connected to the

open ocean through a narrow channel. Thus the extent and depth of the bay significantly vary over a

tidal cycle. This changing geometry determines both the resonant periods and the amplification

factor of the bay. Numerical results confirm the link between observed variability and these specific

topographic features. Results imply that when exceptionally energetic long waves reach the Wells

Harbor entrance (as in the case of a tsunami or meteotsunami) the expected response will be

significantly stronger during low tide than during high tide. Although mean sea level would be lower

in the former case, the currents inside the bay would be stronger and potentially more dangerous.

This tidally modulated response could be extrapolated to other sites with similar topographic

characteristics

A probability-based method to estimate sea level rise and future flooding risks on the

Finnish coast. Hilkka Pellikka, Milla M. Johansson, Ulpu Leijala, Katri Leinonen, Kimmo K.

Kahma Current sea level rise scenarios are subject to large uncertainties, and decision-makers have to

consider how to incorporate the uncertainties in long-term coastal management, e.g. in determining

the building elevations of new coastal infrastructure. Preparing for the worst case is usually not cost-

effective. Rather, the risk level chosen should depend on the potential damage in case of flooding. To

be highly valuable for decision-making, flood risk analysis should provide estimates of flood levels

with different probabilities in the future. We present the method used to make such estimates on

the coast of Finland in the Baltic Sea.

The foundation of our calculations are the long (ca. 100 years) tide gauge records from the Finnish

coast. Historically, sea level has been declining relative to land in Finland because of postglacial land

uplift. We determine the rate of land uplift as a residual trend once the effects of global mean sea

level rise and changes in the wind climate have been removed from the tide gauge time series. The

land uplift is expected to continue with a constant rate for the next few centuries.

We construct a probability distribution of sea level rise in 2000-2100 using an ensemble of recently

published predictions, which have been scaled to take into account regional deviations from the

global mean. In the resulting distribution, the 5-95% range of global mean sea level rise is 33-156 cm.

Regional effects reduce the upper limit by an estimated 20-25% on the Finnish coast. By combining

this distribution with an exceedance frequency distribution of short-term sea level variations, derived

from the last 30 years of measurements, we can estimate the probabilities of different flood levels in

the future.



Combining sea state and land subsidence rates in an assessment of flooding hazards at the

Danish North Sea coast. Carlo Sørensen, Niels Broge, Per Knudsen, Ole B. Andersen The paper presents hitherto unpublished tide gauge (TG) series from the Danish North Sea coast and

investigates their data quality and variability in mean and extreme water levels. Especially TG

benchmarks are subject to a close scrutiny as several stations are placed on sandy barriers liable to

exhibit short and longer term vertical movement, and where only recently TGs have been linked and

related to the Danish vertical datum, DVR90, making the assessment of e.g. SLR difficult. Knowledge

about sea state is important in relation to climate change (CC) effects on erosion and flooding. Here,

flooding hazards are evaluated in a case study in the town of Thyborøn that combines SLR, extreme

value analysis, and local subsidence (2-7 mm/y) and we provide (preliminary) results on the

challenges faced by the local community and their efforts opting for the best adaptation measures

based on current knowledge and projections of regional CC impacts. Sea level research and the

absorption of this knowledge into adaptation schemes in a vulnerable coastal region are discussed.

Special session on Mediterranean sea level

Oral Presentations

To what extent can Mediterranean sea level evolve differently from global sea level rise?.

Gabriel Jordà, Damià Gomis, Marta Marcos During the last decades, Mediterranean sea level has been rising at a lower rate than the global

ocean. In addition to the recognised role of the atmospheric pressure between the 1960s and the

1990s, a salinity increase has also been claimed as a possible mechanism to explain the lower sea

level rise. More important, it has been hypothesized that the continuous salinity increase projected

by most models could partially compensate future global sea level rise, so that by the end of the 21st

century Mediterranean sea level could be significantly lower than global sea level. These claims have

generated confusion on the fate of Mediterranean sea level under climate change.

In this presentation we will first argue why changes in the salinity of the Mediterranean Sea do not

have a significant impact on the basin averaged sea level. Furthermore we will propose a novel

approach to combine the information from global and regional models to generate a large ensemble

of Mediterranean sea level projections for the XXI century. The results from such projection

ensemble suggest that, independently of the emission scenario, Mediterranean sea level will evolve

similarly to the NE Atlantic. Namely, the projections show a slight increase in the baroclinic slope

along Gibraltar Strait and a small increase in the atmospheric pressure over the basin relative to the

Atlantic, which altogether would result in a decrease of about 5 cm in the Mediterranean sea level

relative to the NE Atlantic. In turn, the ensemble mean sea level shows that the NE Atlantic will be

about 15 cm higher than global mean sea level by the end of the 21st century. This altogether would

result in a Mediterranean sea level about 10 cm higher than global mean sea level.



On the connection between the sea level variability in the Mediterranean and in the Black

Seas. Denis Volkov, Felix Landerer The Black Sea is part of a large-scale climatic system that includes the Mediterranean and the North

Atlantic. The seasonal sea level budget shows similar contributions of fresh water fluxes

(precipitation, evaporation, and river discharge) and the Black Sea outflow, while the impact of the

net surface heat flux is smaller although not negligible. We find that the nonseasonal sea level time

series in the Black and Aegean (Mediterranean) Seas are significantly correlated, the latter leading by

~1 month. This lag is attributed to the adjustment of sea level in the Black Sea to externally forced

changes of sea level in the Aegean Sea and to the impact of river discharge. The nonseasonal sea

level budget in the Black Sea is dominated by precipitation and evaporation over the sea itself, but

external processes such as river discharge and changes in the outflow can also cause some large

synoptic-scale sea level anomalies. Sea level is strongly coupled to terrestrial water storage over the

Black Sea drainage basin, which is modulated by the North Atlantic Oscillation (NAO). We show that

during the low/high NAO southwesterly/northeasterly winds near the Strait of Gibraltar and

southerly/ northerly winds over the Aegean Sea are able to dynamically increase/decrease sea level

in the Mediterranean and Black seas, respectively.

Meteotsunamis in the Mediterranean Sea: rare but destructive extreme sea level events

occurring under specific synoptic conditions. Ivica Vilibic, Jadranka Sepic This presentation will encompass state-of-the-art on meteotsunamis, rare but potentially destructive

extreme sea level phenomenon which occurs in the tsunami frequency band. The tsunami-like waves

are generated by atmospheric pressure disturbances propagating over a shelf, resonantly pumping

energy into the ocean during those situations in which speed of air pressure disturbance equals

speed of long ocean waves. These propagating atmospheric disturbances are normally associated

with specific atmospheric conditions which enable generation and non dissipative propagation of

low-tropospheric waves over long distances.

Meteotsunamis have been documented to appear in coastal waters of all continents and world seas,

with a substantial coastal impact in low-tidal basins such as the Mediterranean. Destructive

meteotsunamis normally affect a limited area not wider than a few hundreds of kilometres; however,

the extreme events like the one occurring in the Mediterranean between 22 and 27 June 2014 may

be composed of a chain of destructive events, affecting coastal regions over a few thousands of

kilometres.

In the Mediterranean, destructive meteotsunamis are documented to occur in the Balearic Islands,

the Adriatic Sea, western Sicily coast, the Maltese Islands and the western Black Sea coast, with

several meters high waves occurring once in a decade. Meteorological tsunamis normally occur

during warm seasons when inflow of warm and dry air from Africa is persistent in the lower

troposphere, and when a strong and unstable mid-tropospheric south-westerly jet stream can

become a dominant atmospheric feature, serving as a generating and reflecting layer for surface

atmospheric disturbances over long distances. Damages to coastal infrastructure during destructive

meteotsunami events can be up to several millions of Euros and higher, due to both destructive sea

level waves and severe currents in harbour or bay constrictions. Meteotsunamis have also been

suspected to be responsible for a loss of human lives in an event that hit Algerian coastline in August

2007. Less prominent high-frequency events, which cause no damage, but are registered on tide

gauges, occur several times a year throughout the Mediterranean. These events may impact statistics


Palma de Mallorca, June 10-12, 2015 of extreme sea levels in an area, but can also provide an opportunity to study meteotsunamis in

more detail.

Sea level at 2ka BP in the Balearic Islands from Roman age coastal quarries. Fabrizio

Antonioli, Marcus Heinrich Hermanns, Marco Anzidei Along the coasts of Ibiza and Mallorca (Balearic Islands, Spain) have been identified submerged

coastal quarries of roman age which are of great interest for the study of the relative sea level

changes during the last millennia. These were carved on sedimentary carbonate coasts, as in other

sites of the Mediterranean basin, at elevation above sea level. Here we show the results of

observations and measurements collected at the four sites: Sain Jordan in Mallorca, Port d'es

Torrent, Ses Portes and Cap Jueu at Ibiza. Once field observations have been corrected for tide

amplitudes at the time of the surveys by tide gauge data from the nearest stations, lowest cuttings

were placed at elevations between -0.7 and -0.3 meters. Since the Balearic islands are located in a

tectonically stable region, the elevation of the quarries, after they have been interpreted for their

functional elevations, are in agreement with a sea level at 2ka BP lowers than today of about 1.3 m,

in good agreement with the estimates of Lambeck and Purcell (2005). These observations, that are in

contrast with Dorhale et al. (2010), suggest that since the last 2 ka the Balearic Islands underwent to

glacio-hydro-isostatic movements similar to Sardinia, in absence of significant tectonic events.

Evolution of sea level and other variables on the XXI century: a picture derived from

Vanimedat II and ESCENARIOS projects. Enrique Álvarez Fanjul, Damià Gomis, E.

Rodríguez-Camino, Marta Marcos, Gabriel Jordà, R. Aznar, J. C. Sánchez-Perrino, A.

Martínez Asensio, J. Llasses, Elena Padorno, Begoña Pérez, M. N. Tsimplis, F.M. Calafat,

Samuel Somot, F. Sevault, F. Adloff, J. M. Rodríguez An overview of the results of climate change studies on the Mediterranean Sea, made over the last

decade in the framework of Vanimedat II and SCENARIOS projects, is presented. The evolution of the

main marine physical variables (waves, sea level, currents, water temperature and salinity) is

analyzed, as well as changes in atmospheric variables with important impact on marine dynamics

(heat and fresh water fluxes, wind and atmospheric pressure). In order to fulfill this objective, long

term numerical simulations have been carried out: WAM has been employed for reproducing wave

dynamics, Nivmar for sea level residual, RCA for atmosphere and NEMO for sea level, circulation and

hydrography. Integration domains cover all the Mediterranean Sea. The model runs have been

nested, when it has been necessary, into the results of global models generated by other institutions.

New methodologies have been developed to cope with the treatment of sea level data provided by

nested 3D baroclinic models. More specifically, the problem of dealing with changes into the mass

flows has been addressed. In order to obtain a more complete view of the evolution of certain

variables, previously existing simulations from other institutions have been included into the analysis.

As a result of the works, a consistent high resolution description of the evolution of climate change

on the Spanish coast has been obtained. The simulations describe a significant increase in mean sea

level and SST, as well as minor changes in the wave regime. The evolution of salinity is conditioned by

changes in the boundary conditions from global model, which vary significantly from one simulation

to another. These results are consistent with those from the IPCC, but provide a detailed high


Palma de Mallorca, June 10-12, 2015 resolution view over the Mediterranean Sea. The scenarios obtained show the need to develop

adaptation policies on our shores.

Future evolution of sea level extremes along the Mediterranean coastline as produced by

the superposition of storminess and sea level rise. Piero Lionello, Dario Conte, Luigi Marzo,

Luca Scarascia The maximum water level that water reaches at the coast during a storm depends on several factors:

change of mean level (in turn depending on regional steric effects and on remote melting of ice

caps), wave heights, storm surge level. This study attempts to estimate the overall maximum water

level by a simple linear superposition of these factors along the coasts of the Mediterranean Sea. This

is a particularly interesting case as these factors act in opposite directions: sea level is expected to

increase (though the actual future level is uncertain) while reduction of storminess is expected to

decrease future surges and wave height maxima. It is shown that if water mass addition across the

Gibraltar Strait will produce a 10cm sea level rise in the Mediterranean Sea, this contribution will

compensate for the reduction of storminess on water level maxima until mid 21st century. However,

if mass addition will contribute a 20cm sea level rise, then water level maxima during storms will

significantly increase along more than 75% of the Mediterranean coastline.

Posters

On the representation of Mediterranean sea level in regional climate models. Fanny Adloff,

Gabriel Jordà, Samuel Somot, Florence Sevault, Benoît Meyssignac, Thomas Arzouse, Laurent Li,

Serge Planton So far, the question about future sea level change in the Mediterranean remains open. Climate

modelling attempts to assess future sea level change in the Mediterranean were unsuccessful. On

one hand, global models (e.g. CMIP-type models) have a rather low resolution which prevents an

accurate representation of important small scales processes acting over the Mediterranean region - a

basic pre-requisite to achieve a good representation of water masses and sea level in this region.

Additionally, global models often parameterize the water exchange at the narrow Strait of Gibraltar,

which strongly influences the circulation and the changes in sea level in the Mediterranean Sea.

There is thus a need to use high resolution regional ocean modelling to answer the question of

ongoing Mediterranean sea level change. However, up to now, long term regional Mediterranean

ocean models do not integrate the full sea level information from the Atlantic even if it has been

shown that sea level variability in the east Atlantic drives the Mediterranean variability at interannual

and interdecadal scales (Calafat et al, 2012; Tsimplis et al., 2013).

In the present study, we aim to improve the representation of sea level in the regional ocean model

NEMOMED12. The simulation covers the hindcast period 1980-2013. At the Atlantic buffer zone, we

apply a restoring to the temperature, salinity and sea surface height from the reanalysis ORAS4. The

seasonal cycle of the sea surface height is corrected with the altimetry (CCI-sea level data, Ablain et

al. 2015). We evaluate the quality of the simulated Mediterranean sea level through the comparison

with altimetry and reconstructed sea level fields for the pre-altimetric period. We assess the added

value of this new dataset of Atlantic boundary forcing comparing our new simulation with former


Palma de Mallorca, June 10-12, 2015 hindcast simulations from 3 different regional coupled climate models. This validation procedure of

sea level representation in regional ocean simulations is a crucial step before planning climate

change scenario simulations with regional models.

Sensitivity of the Mediterranean sea level to atmospheric pressure and free surface

elevation numerical formulation in NEMO. Antonio Bonaduce, Paolo Oddo, Nadia Pinardi,

Antonio Guarnieri The sensitivity of the dynamics of the Mediterranean Sea to atmospheric pressure and free surface

elevation formulation using NEMO (Nucleus for European Modelling of the Ocean) was evaluated.

Four different experiments were carried out in the Mediterranean Sea using filtered or explicit free

surface numerical schemes and accounting for the effect of atmospheric pressure in addition to

wind and buoyancy fluxes. Model results were evaluated by coherency and power spectrum analysis

with tide gauge data. We found that atmospheric pressure plays an important role for periods

shorter than 100 days. The free surface formulation is important to obtain the correct ocean

response for periods shorter than 30 days. At frequencies higher than 15 days−1 the Mediterranean

basin’s response to atmospheric pressure was not coherent and the performance of the model

strongly depended on the specific area considered. A large-amplitude seasonal oscillation observed

in the experiments using a filtered free surface was not evident in the corresponding explicit free

surface formulation case, which was due to a phase shift between mass fluxes in the Gibraltar Strait

and at the surface. The configuration with time splitting and atmospheric pressure always performed

best; the differences were enhanced at very high frequencies.

Rescuing historic Maltese tide gauge data. Elizabeth Bradshaw The British Oceanographic Data Centre (BODC), through funding from the UK Department for

Business, Innovation and Skills (BIS) 'Breakthrough Fund' have scanned tidal charts from Valletta,

Malta (1876-1926), which were in the archive of the United Kingdom Hydrographic Office (UKHO).

The analogue records were difficult to access and in need of conservation. They have now been

conserved and photographed to produce digital images and these images will be publically available

from www.bodc.ac.uk/data/online_delivery/historical_uk_tide_gauge_data/, preserving one of the

longest and earliest temporal series of sea level data in the Mediterranean.

A vital component of climate change research, long-term sea level records are used to identify global

and regional sea level changes and the changing frequency of storm surges and coastal floods. The

data are used by the Intergovernmental Panel on Climate Change (IPCC) in their reports, which

inform policy on our changing weather. Historical data are unrepeatable measurements and we want

to encourage their rescue and re-use, especially from data-sparse regions. There are no long-term

sea level records in the middle of the Mediterranean, and only one with 50 years of data in the

Southern Mediterranean in the Permanent Service for Mean Sea Level data bank.

We are investigating digitising the images via a citizen science activity, such as the International

Environmental Data Rescue Organization (IEDRO) project, Weather Wizards, where citizen scientists

are helping to digitise pluviograms (rainfall charts). If possible, this system could be adapted for tide

gauge charts.


Palma de Mallorca, June 10-12, 2015 Once the record is digitised, it can be studied to help refine models of climate change, surges and

tsunami propagation in the Mediterranean.

BODC have been working with the Global Sea Level Observing System Group of Experts (GLOSS GE)

on sea level data archaeology (unearthing, preserving, digitising, quality controlling and distributing

historical data) - www.gloss-sealevel.org/data/glossdataarchaeology.html

Long-wave analysis of coastal sea-level records and implications for hazard monitoring and

assessment: an application to the Siracusa, Italy, tide-gauge station. Lidia Bressan, Stefano

Tinti The Siracusa tide-gauge station is part of the TSUNET network, a sea-level monitoring network to

measure and detect tsunamis in Eastern Sicily, one of the most hazardous coastal areas for tsunamis

in the Mediterranean sea. Detection of tsunamis and other anomalous wave conditions is carried out

by using a specific package called TEDA developed by the Tsunami Research Team of the University

of Bologna, Italy. TEDA is a real-time detection algorithm for long period waves structured in two

algorithms that work in parallel: i) the tsunami detection method that detects impulsive long period

waves, like tsunamis, and that it is based on a modified STA/LTA algorithm working on the detided

sea-level instantaneous slope IS and on the background slope BS; and ii) the secure detection

method that computes the detided secure detection marigram (MSD) and identifies waves exceeding

a certain amplitude threshold.

In this work, also exploiting the specific TEDA functions, we analyze the tide-gauge records of

Siracusa. It is found that the sea-level presents a typical spectral content due to the regional and local

coastal morphology and bathymetry, which is reflected also in the functions IS and MSD. The station

exhibits spectral stability on an annual basis, and seasonal variability, with more energetic spectra in

winter months and quieter spectra in summer.

A further analysis focused on the empirical frequency distribution (EFD) of the TEDA characteristic

functions, confirms the annual stability and seasonal variability. Interestingly, it is found that the

EFDs computed on a monthly or longer-interval basis fit well-known probability density functions,

which helps to study the seasonal variations of the sea-level and calls for a theoretical interpretation.

The results of the analysis are presented and discussed.

Mesoscale eddies in the Western Mediterranean Sea. Romain Escudier, Ananda Pascual,

Pierre Brasseur, Lionel Renault Mesoscale eddies are relatively small structures that dominate the ocean variability and have large

impact on large scale circulation, heat fluxes and biological processes. In the western Mediterranean

Sea, a high number of eddies has been observed and studied in the past with in-situ observations.

Yet, a systematic characterization of these eddies is still lacking due to the small scales involved in

these processes in this region where the Rossby deformation radius that characterizes the horizontal

scales of the eddies is small (10-15 km).

The objective of this study is to perform a characterization of mesoscale eddies in the western

Mediterranean. In this objective, we develop a high resolution simulation of the area. Then we apply

three different eddy detection and tracking methods to extract eddy characteristics from the outputs

http://www.gloss-sealevel.org/data/glossdataarchaeology.html


Palma de Mallorca, June 10-12, 2015 of the high-resolution simulation, a coarser simulation and altimetry maps. The results allow the

determination of some characteristics of the detected eddies. The size of eddies can greatly vary but

is around 25-30 km. About 30 eddies are detected per day in the region with a very heterogeneous

spatial distribution. Unlike other areas of the open ocean, they are mainly advected by currents of

the region. Eddies can be separated according to their lifespan. Long-lived eddies are larger in

amplitude and scale and have a seasonal cycle with a peak in late summer, while short-lived eddies

are smaller and more present in winter. The penetration depth of detected eddies has also a large

variance but the mean depth is around 300 meters. Anticyclones extend deeper in the water column

and have a more conic shape than cyclones.

Improved satellite altimeter mapped sea level anomalies in the Mediterranean Sea. Marta

Marcos, Ananda Pascual, Isabelle Pujol The new gridded Mediterranean sea level anomaly product recently released by AVISO (DT14) is

evaluated and compared with the earlier version (DT10) at which it is aimed to substitute.

Differences between the two products are found along coastal regions, where the new version

captures more variability (up to 10% more) and trends locally differ by up to 1 mm/yr for the

altimetric period. Coastal tide gauge observations have therefore been used as the basis for

quantifying changes in DT14. Correlation and variance reduction in available monthly tide gauge time

series are improved in more than 80% of the selected sites, resulting in an overall higher skill to

recover coastal low frequency sea level signals. Results for higher/lower order percentiles were also

explored and showed different performances depending on the site, although with a slight overall

improvement. A comparison with tide gauges on a daily basis using wavelet analysis reveals that

altimetry gridded products are still far from recovering higher frequency coastal sea level signals

despite some advances have been achieved thanks to the daily temporal sampling of DT14.

Determination of Mean Dynamic Topography over the Mediterranean Sea from Jason-2

Altimetry Measurements and EGM2008 Data. Ali Rami, Sofiane Khelifa The ocean surface must be surveyed in order to determine the dynamic topography, tides, time-

variations etc…

The ocean dynamic topography, which is the distance between the geoid and the instantaneous sea

surface height and which reflects the ocean dynamics, is a primary oceanography unknown.

The processing of 5 years of Jason-2 satellite altimetry measurements is done after the estimation of

the environmental geophysical and orbital parameters corrections, permit us to determinate the sea

surface height with 1 cm of precision, while using the Earth Gravitational Model EGM2008 (geoid)

based on a combined data (GRACE, terrestrial and altimetry measurements,….) we can calculate the

mean dynamic topography of the Western Mediterranean sea. The variation of the obtained mean

dynamic topography is between -1.12 and 1.12m.

The obtained surface is compared with the Mean dynamic topography provided by AVISO Altimetry

(RioMed).



Interannual variability of the Surface Geostrophic Circulation of the Mediterranean Sea. M.

Sempere, S. Esselborn, I.Vigo The most recent advances in the geoid determination, provided by the Gravity Field and Steady-State

Ocean Circulation Explorer (GOCE) mission, together with the continuous monitoring of the sea

surface height by the altimeters on board of satellites have made possible to retrieve ocean surface

currents directly through remote sensing. A reliable estimation of the ocean Dynamic Topography

(DT) that, in turn, requires reliable measurements of the Absolute Sea Level (ASL) height and an

independent geoid are the key to the determination of the Surface Geostrophic Currents (SGC).

Nowadays it is possible to combine more than 20 years of altimetry data with a geoid model based

on GOCE data to obtain the DT with an unprecedented precision and accuracy. In addition, the

improved accuracy in satellite altimetry data has allowed to determine ASL maps at weekly

resolution.

New insights into the structure and variability of the Mediterranean Sea's surface circulation are

obtained through the analysis of the long series, for the period spanning 1992–2014, of weekly SGC

maps gridded at one eighth degree longitude and latitude resolution resolving spatial scales as short

as 70 km. For presentation, this data set is averaged monthly and the results are interpreted and

validated with simulations from ECCO/Mercator models and/or drifter observations where possible.

Seasonal Cycle of Surface Geostrophic Circulation of the Mediterranean Sea. M.Sempere, I.

Vigo, M. Trottini, S. Esselborn The most recent advances in the geoid determination, provided by the Gravity Field and Steady-State

Ocean Circulation Explorer (GOCE) mission, together with the continuous monitoring of the sea

surface height by the altimeters on board of satellites have made possible to retrieve ocean surface

currents directly through remote sensing. A reliable estimation of the ocean Dynamic Topography

(DT) that, in turn, requires reliable measurements of the Absolute Sea Level (ASL) height and an

independent geoid are the key to the determination of the Surface Geostrophic Currents (SGC).

Nowadays it is possible to combine more than 20 years of altimetry data with a geoid model based

on GOCE data to obtain a the DT with an unprecedented precision and accuracy. In addition, the

improved accuracy in satellite altimetry data has allowed to determine ASL maps at weekly

resolution.

In this work, weekly SGC maps of the entire Mediterranean Sea for the period spanning 1992–2014

gridded at one eighth degree longitude and latitude resolution resolving spatial scales as short as 70

km are used to extend previous research on the Mediterranean surface circulation seasonality. To

investigate the annual and semiannual cycles in SGC, we least squares fitted the corresponding

harmonics independently for each velocity component. For presentation, the data sets are averaged

monthly and the results are interpreted and validated with simulations from ECCO/Mercator models

and/or drifter observations where possible.



High-frequency sea-level oscillations in the Mediterranean Sea: analysis and synoptic

preconditioning. Jadranka Sepic, Ivica Vilibic, Amaury Lafon, Loic Macheboeuf, Zvonko

Ivanovic During the last decade many national tide gauge networks have been upgraded to measure sea level

with a higher sampling rate (1-min). Concurrently, through a number of tsunami warning systems

and data sharing services, these data became freely available to scientific community, allowing for

regional and ocean studies of high-frequency component of sea level oscillations.

Presented study focuses on an analysis of 1-min sea level time series collected at 32 Mediterranean

tide gauge stations with 4 or more years of data available between 2008 and 2014. The data is

available at the IOC website (http://www.ioc-sealevelmonitoring.org). Sea level time series were de-

spiked, de-tided, linearly interpolated, high-pass filtered and analysed. Several important points were

revealed: (i) high-frequency sea level oscillations are often widespread and can affect areas from the

eastern Spanish to the western Greek coast; (ii) during the Mediterranean-wide events, oscillations

typically first occur in the Western Mediterranean, and then their occurrence propagates within the

next few days to the Eastern Mediterranean (Greece); (iii) oscillations occur throughout the year but

are, depending on area, strongest from April to August; and (iv) high-frequency sea level oscillations

are often associated with higher-than-average mean sea level conditions, adding to a possible danger

of flooding; also, they are occasionally related to dangerous meteotsunami events.

Synoptic conditions observed during the 48 strongest events were analysed in more detail. These

events typically occur during: (i) presence of low mean sea level pressure with a centre northwest

from the affected area; (ii) inflow of warm African air in the lower troposphere; (iii) strong south-

western winds and the jet at mid-tropospheric levels embedded in (iv) instable atmospheric levels.

Analysis of sea level data combined with statistics of appearance of favourable synoptic pattern has a

potential to further contribute to the flooding hazard assessment.

Mean sea level secular trends from PSMSL RLR data: A case study for the Mediterranean

basin. Hebib Taibi , Mahdi Haddad In this paper, Dynamic Harmonic Regression (DHR) model is applied to the investigation of the long-

term evolution of sea level time series monitored in Mediterranean coastal areas and recovered from

the Permanent Service for Mean Sea Level (PSMSL) database.

The analysis of 9 long monthly mean sea level series indicate that the Mediterranean mean sea level

has significantly been raised during the last century. The various results obtained in this paper are

promising and show that the sea level behavior in different stations is far from uniform. As extremity,

while in Split - Gradska Luka station, the sea level has indeed risen during the period 1955-2008 by up

to 0.43 ± 0.06 mm/year, the sea level Venezia (Punta Della Salute) has raised with a rate of 3.01 ±

0.03mm/year during the period 1909-2000.

Relative sea level trend and long term variability in the Northern Mediterranean from tide

gauge data: implications for future projections. Antonio Vecchio, Marco Anzidei We analyzed the longest tidal records available for the Mediterranean region at eight tide gauge

stations distributed along the coasts of Italy, France, Slovenia and Croatia. Data were retrieved from


Palma de Mallorca, June 10-12, 2015 the Permanent Service for Mean Sea Level and were collected in the 1872-2014 time span for the

tidal stations of Genova and Marseille. From these long records we identified the contributions of the

nonlinear global warming signal and the long term natural variability in the sea level trend. Through

the development of a simple low order theoretical model we investigated the combined effect of the

global sea level increase and the decadal natural variability on the future sea levels at the analyzed

stations. Finally, we tentatively estimated the future sea level rise up to 2100, by including the IPCC

predictions in our analysis. Here we show and discuss the expected sea levels at the individual

stations that will have implications for coastal flooding of lowland areas located in the investigated

region.

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