Core Theme 1

WP 1.1

Task 1.1.1: Assessment of millenium-scale

simulations and role of external forcing

Compare simulated (signatures of) THC variability on interdecadal to centennial time scales with palaeo-observations from WP1.2 [LOCEAN, MET-O, MPI-M, NERSC]

Compare simulated key processes of THC dynamics with observations from CT3 [MPI-M]

Design a procedure for coordinated model testing [LOCEAN] and apply to the models [IFM-GEOMAR, LOCEAN, MET-O, MPI-M, NERSC]

Investigate the role of external forcing on THC variability [MET-O, MPI-M, NERSC, IfM GEOMAR]

17

17.5

18

18.5

19

19.5

20

-3

-2

-1

0

1

2

3

4

5

1400 1500 1600 1700 1800 1900 2000

SS

(m

ea

n) A

MO

Ind

ex

Year A.D.

ISOW & AMO in phase

vigorous ISOW

sluggish ISOW

warm phase AMO

cold phase AMO

Mean Sortable Silt at Gardar drift(this study)

Reconstructed AMO basedOn three rings (Gray et al., 2004)

WP 1.2 RESULTS - MEAN SORTABLE SILT AT GARDAR DRIFT

Gadar Drift data suggest that basin-wide warm phase is associated with vigorous ISOW flow

Role of processes

Monthly mean observed (blue) and modelled (red) Faroe Bank Channel overflow

Modeled annual mean Denmark Strait (upper) and FBC (lower) overflow

Olsen et al., 2008

Role of processes

Modeled annual mean Denmark Strait transport from NCEP forced ocean-only experiment (grey) and assimiltion run with coupled AOGCM (green)

Matei et al., in prep.

Internal variability vs. External forcing as a pacemaker for Atlantic multidecadal

variability?

Otterå et al 2009

…but this finding appears to be model (and forcing) dependent….

Task 1.1.2: THC variability on decadal to

centennial time scalesInvestigate mechanisms responsible for low-frequency THC

variability with focus on overflow, deep water formation and its preconditioning [LOCEAN, MET-O, MPI-M, NERSC]

Design [MPI-M] sensitivity experiments to investigate the impact of changes in overflow and deep water formation on the THC [LOCEAN, MET-O, MPI-M, NERSC]

Assess the role of THC variations on recent changes in North Atlantic heat/fresh water content [MET-O]

Design budget and statistical analysis diagnostics [MET-O] and apply to the models [LOCEAN, MET-O, MPI-M, NERSC]

Variability: No consensus among state-of-the-art climate models

MPI KCM

100 10100 10

CSIRO GFDL

Power spectra: Maximum Atlantic MOC at 30N, CMIP3 pre-industrial control simulations

Period (yr)Period (yr)Courtesy: Jin Ba

Role of overflow variations for MOC

Denmark Strait Overflow Transp. and MOC anomalies @ 1085m

3

0

-3Anomaly (Sv)Jungclaus et al., in prep.

Sensitivity experiment: supress density variations in NS

Denmark Strait Overflow Transp. and MOC anomalies @ 1085m

3

0

-3Anomaly (Sv)Jungclaus et al., in prep.

Task 1.1.3: Ocean-atmosphere feedbacks and

climatic impact of THC changes

Statistical analysis of lead/lag relationships to investigate the relative role of (un)coupled modes in explaining the low-frequency THC variability [LOCEAN, MET-O, MPI-M, NERSC], aided by sensitivity experiments [LOCEAN, MPI-M, NERSC]

Perform partial coupled experiments with focus to identify to which extent the Atlantic Multidecadal Oscillation is part of a coupled climate mode [LOCEAN, MET-O, MPI-M, NERSC]

Investigate the impact of THC changes on European and Arctic climate [LOCEAN, MET-O, MPI-M, NERSC]

Ocean-atmosphere feedbacks

Msadek & Frankignoul, 2009

The WP1.1 model zooNERSC: Bergen Climate Model (BCM):ARPEGE (T42/L31) + MICOM (2.4°, L35)

700yr long control integration 1400-1999 solar and volcanic forcing 1850-1999 solar, volcanic, GHG and aerosol forcing ensembles for selected periods planned scenario integration

MPI-M: MPI-M Earth System Model (COSMOS) ECHAM5 (T31/L19) + MPI-OM, 3°, L40 + carbon cycle)•3000yr long control integration•800-2005 solar, volcanic, land use change, GHG and aerosol forcing (ensemble of 5), •single forcing experiments•alternative solar forcing (ensemble of 3)

The WP1.1 model zooLOCEAN: IPSLCM4_v2: Atm: 96x71x19, Ocn: 2°x2°

1000yr long control integration 950yr solar and CO2 forcing solar, volcanic and CO2 forcing (running)

higher-resolution runs planned:

METO: HadCM3 1.25° ocean,L205700yr pre-industrial control1500-2000 „natural 500“, solar, orbital, volcanic aerosol, preindustrial GHG (1750), 1750 land surface1750:2000: „all250“: as natural 500 + GHG & aerosol emission history, land-use-change, ozone1860-2000 4 member anthropogenic + natural ensemble

The WP1.1 model zooIfM GEOMAR: KCM: ECHAM5 (T31/L19) + NEMO 2°x2°/L31)

5000yr long control integration idealized solar forcing runs

higher-resolution runs planned

IN SUMMARY:All modelling groups have provided long integrationsCross-model validation is going on using >1000 yr controlexperiments:Overflow characteristicsSub-polar-gyre characteristicsAMO vs. AMOCSea ice variability

WP1.1 summary

All modelling groups have provided long integrationsCross-model validation is going on using >1000 yr controlexperiments:Overflow characteristicsSub-polar-gyre characteristicsAMO vs. AMOCSea ice variability

Things to do

Assess similarities and differences in the THC as represented in the various models and millennium-scale reconstructions

representation of processes

characteristics of internal variability

climate response to THC changes

THC response to external forcings

What causes the differences between the models?

Define common analyses tools and prepare publication strategy

WP 1.2: Participants: BCCR and CNRS (Gif-sur-Yvette)

Task 1.2.1. Characterize changes in the deep and intermediate return flow of THC;Determine how much it changed, which components, and why.

Task 1.2.2. Characterize the upper limb of THC—Variations in the inflows to the Nordic Seas.

Task 1.2.3. Characterize climate and thermocline evolution over the last millennium

Variability in ISOW vigor over the last 1300 years and its relationship to climate

U. Ninnemann, T.L. Mjell, H. Kleiven and I. Hall,

Bathymetry of the northern North Atlantic and the Nordic Seas. Location of cores MD03-2664/2665 and ODP 983/MC09 are marked with red dots (Modified from Smith and Sandwell, 1997)

Linkages to AMOC?How have Nordic Seas overflows varied?

Study Area—ISOW variability on Gardar drift

Latitude: 60°19’ NLongitude: 23° 58’ WDepth: 2081 m

GS06-144-09 MC-D

IR

NIIC

Iceland-Scotland Overflow Water (ISOW)

Curry & Mauritzen, 2005

~1400 AD

Location in the core of ISOW overflow

Y= 19.833 – 0.00082278x R= 0.43356

I II III IV

~1400-1520 AD

~1521-1618 AD ~1618-1721 AD

~1721-1820 AD

~1820-1937 AD ~1937-1996 AD

WP 1.2 RESULTS - MEAN SORTABLE SILT AT GARDAR DRIFT

• Multidecadal to centennial variability in ISOW vigor and chemical properties over the last ~600+ years

• ISOW flow variability is coherent across a range of depths and space (not a local signal)

• During the past ~350 years ISOW vigor is in phase with reconstructed AMO on both inter-decadal and centennial timescale—within the error of our age models.

• This strong coherence suggests that low frequency variability in key components of AMOC is coupled to basin-wide temperature perturbations

Summary of Observations

Eirik sediment drift – DSOW & DWBC variability

~ 2006 AD

~600 AD

Curry & Mauritzen, 2005

GS06-144-03MC A

Latitude: 57°29’ NLongitude: 48° 37’ WDepth: 3432 m

Deep Western Boundary Current (DWBC)

Mann and Jones (2003)NH tmp. reconstructions

Benthic oxygen isotopesFrom MD03-2664; 3 pt.smooth(Kleiven et al., in prep)

Natural variability in the deep water masses

WP 1.2.3: Towards the reconstruction of the thermocline

variability in the North Atlantic during the last millennium

T. Bouinot, E. Cortijo, A. Govin, C. ClérouxLSCE/IPSL (Gif/Yvette, France)

Study sites:

sediment cores

SST August

Already studied

Future work

How to reconstruct the thermocline variability?

Summer mixed layer

Seasonal thermocline

Temperature

Water depth

Permanent thermocline

Deep-dwelling foraminifera:1. Globorotalia inflata2. Pulleniatina obliquiloculata

1. 2.

Planktic foraminifera1. Globigerinoides ruber2. Globigerina bulloides

2.1.

Core MD99-2203 (35°N, 75°W, 620 m)

SST August

C. Cléroux, PhD thesis

Future work: to better trace the extension of the subtropical & subpolar gyres in the North

Atlantic

From Hatun et al. Science 2005

Subtropical gyre water

Subpolar gyre water

MD08-3182Q

MD03-2674Q(56.4°N, 27.8°W, 2830 m)

MD03-2678Q(58.8°N, 26.0°W, 2603 m)

Coretop’s date 2000 a is around

MD03-2674Q 671.5 a ± 30 a 50 cm

MD03-2678Q 308.5 a ± 30 a 35 cm

Deliverables

Deliverables

All WP 1.1 partners have control integrations of 1000 to 6000 years

forced integrations over the millennium are accomplished or ongoing, some forced integrations have been run in ensemble mode

analyses focus presently on the assessment of THC characteristics and mechanisms

Summary WP 1.1

WP1.2: reconstructions of the strength of the ISOW over last millennium ready, upper ocean T and S in progress.

Reconstruction of integrated overflows south of Greenland as well as upper ocean T, S, and chemical properties in progress

New cores (Gadar Drift and Bay of Biscay) give detailled information on the structure of the thermocline

Hydrographic reconstructions from the inflow region (Faroe transect and Norwegian Sea ready for the last 400-600 years, will be extended back in time

Summary WP 1.2

Data from WP3 for process understanding:

- Overflow transport timeseries

-Watermass characteristics

monthly basis /

Some key data should be put somewhere together, for instance the data from CT1 on overflow transport / overflow overturning

Give information on variability on time scales most relevant for decadal prediction (CT4)

CT1 and other CTs