Toward an Assessment of Ocean Acidification inthe Adriatic Sea and Impacts on the Biogeochem-istry of Marine Carbonate System

A. Luchetta, C. Cantoni, G. Catalano, S. CozziInstitute of Marine Sciences, CNR, Trieste, Italyanna.luchetta@ts.ismar.cnr.it

Abstract

The increase of CO2 amount in the atmosphere has created great concern: itwill in all probability result in changes in temperature, precipitation and/or their sea-sonal amplitudes with consequences not only on sea level rise but also on chemicalequilibrium of the CO2 system in seawater, mainly reducing pH and carbonate ionconcentration (Ocean Acidification). The process is now well documented in fielddata from all around the world. However is not sufficiently witnessed in the Mediter-reranean Sea, due to the scarcity of good quality data. On this concern, results for theAdriatic Sea are presented: from experimental measures of pH and total alkalinity,two seasonal pictures of pH and carbonate system parameters have been drawn. Inaddition, a pH decrease of 0.063 pHT units with related chemistry changes has beeninferred in the North Adriatic Dense Water (NAdDW) over the two last decades.These results, although preliminary, merit attention as confirm that N. A. sea hasbeen affected by OA, being sensitive to the climate forcing. Potential impacts of OAare several and should be assessed, as many might even exacerbate hyopoxia/anoxiaevents, already affecting the area. OA might also affetc the food web, as the car-bonate reduction has the potential to alter the distribution and abundance of marineorganisms that use calcium carbonate to build their shells or skeletons (corals, plank-ton) and the organisms that depend on them for survival (fishes, marine mammals).

1 Introduction

Over the past 250 years the carbon diox-ide (CO2) concentration in the atmospherehas continuously raised, reaching values upto 380 ppmv, that have never been expe-rienced on Earth in the last 800,000 years[1]. It is now largely recognized that thisincrease was mainly determined by humanactivities related to the combustion of fos-sil fuels and deforestation, which, in allprobability will result in changes in tem-perature, precipitation and/or their seasonal

amplitudes with consequences on the sta-bility of our climate. Since the beginningof the industrial age, between 1800 and2000, mankind has emitted 361 Gt C tothe atmosphere [2]. The ocean has ab-sorbed approximately 155 Gt C: this makethe world ocean the largest sink of anthro-pogenic CO2, without it atmospheric car-bon dioxide levels would be approximately450 ppmv today [2, 3]. The uptake of CO2

by the ocean is primarily due to physico-chemical processes. As CO2 solubilises inseawater, it behaves like a weak acid that

Oceanography

dissociates according to:

CO2(atm) CO2(aq) + H2O

H2CO3(aq)

H+(aq) + HCO−3 (aq)

H+(aq) + CO2−3 (aq),

leading to an increase of [H+] and to adecrease of pH value (pH = -log [H+]).The overall process resulting in a reduc-tion of pH and shifts in carbonate specia-tion is referred to as “Ocean Acidification”(OA). Climate change and ocean acidifica-tion are both caused by the increasing ofatmospheric CO2 levels and ocean acid-ification has been recently referred to as“The other CO2 problem” [4]. However, ifclimate change forecasts suffer from someuncertainties, in contrast OA is a well pre-dictable consequence of rising atmosphericCO2. On global scale, OA is now doc-umented with hydrographic surveys, timeseries data and well verified from models[5, 6, 7, 8, 9, 10].Since preindustrial times, the averageoceanic surface pH has fallen down byapproximately 0.1 units, from approxi-mately 8.21 to 8.10 [11], and is ex-pected to decrease a further 0.3–0.4 pHunits [9] if atmospheric CO2 concen-trations reachs 800 ppmv (the projectedend-of-century concentration according tothe Intergovernmental Panel on ClimateChange (IPCC) business-as-usual emissionscenario). Ocean acidification alters sea-water speciation and biogeochemical cy-cles of many elements and compounds, in-cluding nitrogen, phosphorus, silicon andtrace elements (iron, zinc), thus chang-ing their availability for phytoplankton [4].Acidification of ocean water occurs in tan-dem with decreases in carbonate ion (CO=

3 )

concentration and saturation state of cal-cium carbonate minerals (CaCO3), whichdirectly impact the formation and disso-lution. In the marine environment, car-bonate formation is largely a biotic pro-cess: corals, foraminifera, coccoliths, bi-valves and other marine organisms formshells and skeletons composed of a varietyof carbonate minerals.CO2 solubility in seawater is the highestat low temperatures, thus the most pro-nounced effects of OA on marine ecosys-tems are expected to affect sub polar seasand not the Mediterranean Sea, a semi-enclosed water body in a temperate cli-mate region [12]. In addition Mediter-ranean seawater is characterized, on aver-age, by higher alkalinity than open ocean,that would increase the buffering capacityof the Mediterranean waters thus limitingOA. Notwithstanding, ocean acidificationis particularly interesting to be investigatedin the Mediterranean Sea as the basin issupposed to be very sensitive to the globalclimatic change (giving a rapid response),because of the faster water renewal (shorterresidence times of water masses) comparedto the oceans and the high anthropogenicpressure concurrently with the high CO2

carrying capacities of the cold surface wa-ters in the northernmost regions. Conse-quently the Mediterranean area would al-ready present significant pH drops [12], es-pecially in the regions where cold densewaters are formed. But the OA processin the Mediterranean Sea is not sufficientlywitnessed, due to the scarcity of good qual-ity pH measurements, particularly in theEastern sub-basin [12, 13].The Adriatic basin is one of the few siteswhere dense waters are formed in wintryseason. This process represents an im-portant driving engine for the circulationand ventilation of deep waters of the east-

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ern Mediterranean Sea. Adriatic densewaters form either on the northern shal-low shelf of this basin, North AdriaticDeep Water (NAdDW), and by the deepSouthern Adriatic Pit, Adriatic Deep Water(ADW). Afterward, they usually sink andoutflow through the Otranto Strait sill (750m), which controls the export to Ionianand Eastern Mediterranean Seas [14]. TheAdriatic Sea has been therefore consideredthe dominant source region of dense wa-ters for the Eastern Med until the occur-rence of the Eastern Mediterranean Tran-sient [15], in the end of 1980’s, whichabruptly changed the deep circulation pat-tern. At present time, the deep circula-tion scheme seems to have switched backto pre-Transient conditions.The Adriatic basin is subjected to highanthropogenic pressure, being surroundedby very industrialized regions that releaseCO2 into the atmosphere. There car-bon dioxide uptake and ocean acidificationwould be particularly effective, due to lowtemperature of surface waters, especiallyin the northernmost part which representsthe largest shelf area of the entire Mediter-ranean region [14]. According to the deepand bottom layers circulation scheme theAdriatic dense water masses are expectedto have the possibility of spreading acid-ified waters around, through the EasternMediterranean.Therefore monitoring the interannual vari-ability of pH and studying the forcings onthe carbonate system in the Adriatic Seaappears worth and new. Here are presentedthe major findings of the research activitycarried out by ISMAR Trieste in last fewyears, within a few national and europeanprojects and in collaboration with local en-vironmental agency.

2 MethodsThe determination of pH was performed bythe spectrophotometric method describedby Dickson [16], values are expressed onthe total H+ scale (pHT , [H+] in µmolH+/kgSW ), at 25 °C (as recommendedby protocols for quality control of results),with a precision of ± 0.003 pH units.To our knowledge the dataset is the firstcollected with such a precision over thewhole basin. The Total Alkalinity (AT )has been measured by potentiometric titra-tion in an open cell, with precision of± 3.0/kgsw, the accuracy was controlled againstcertified reference materials (CRM) sup-plied by Andrew Dickson (Scripps Institu-tion of Oceanography, San Diego, USA).Both the in situ fugacity of carbon dioxide(f CO2) and the in situ pH values were cal-culated with the CO2 calculation program(CO2SYS program) developed by Lewisand Wallace [17] by using the parameterspHT , AT , silicate, phosphate, T in situ andS for each discrete sample. However, pHdistributions in Figures 1, 2, 3, are shown atfixed temperature (25 C) because fixing thetemperature means “lock” the equilibriumreactions of the carbonate system, gettingrid of the temperature contribution. Thusany comparison between different watermasses and different seasons is more im-mediate.

3 Results and discussion

3.1 pHT spatial and seasonalvariability in the AdriaticSea

In Figures 1 and 2 are reported the distri-butions of potential density (σt), apparentoxygen utilization (AOU) and pHT gath-

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Figure 1: Potential density (σt), apparent oxygen utilization (AOU), pHT at 25 C distri-butions along the Adriatic Sea in February 2008. In the smaller frames a more detailedview of the North Adriatic shelf area is given.

ered at meso scale in the Adriatic basin.They were measured during two surveys,conducted in February and October 2008,within the frame of VECTOR (national)and SESAME (EU FP-6) projects.In February 2008 the North Adriatic shelfwas involved in a dense water forma-tion event, being shallow and exposed tocold dry winds (Bora) as reported alsoin the past [18]. The water column waswell mixed, ventilated down to the bottom(mean AOU = -4.1 µM), cool (10.35 C)and dense (σt > 29.3 kgm−3). The T/Sproperties were in agreement with those ofNAdDW, that are among the densest of theMediterranean Sea [19].The whole water column was rich of DIN

(1.00-7.00 µM) and SiO2 (1.20–5.33 µM),even at surface, thus suggesting that intenseprimary production had not yet started.The pHT values were homogeneously dis-tributed in the water column, ranging be-tween 7.917 and 7.973 pHT units, witha mean value of 7.946 in the core ofdense water mass (NAdDW). Biologicalprocesses such as primary production andremineralization of organic matter, couldcontribute to the final pH of seawater byconsuming or adding CO2. Such a homo-geneous distribution of all parameters overan extended area mirrored the winter timeconditions encountered. The pHT valueswere driven by the high CO2 solubility incold seawater while intense biological pro-

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Figure 2: Potential density (σt), apparent oxygen utilization (AOU), pHT at 25 C distri-butions along the Adriatic Sea in October 2008. In the smaller frames a more detailedview of the North Adriatic shelf area is shown.

cesses had not yet started (as indicated byAOU and nutrients values), that is typicalof wintry season.f CO2 values calculated at fixed tempera-ture (25°C) were high (avg 583 µatm) thusindicating that such cold and ventilated wa-ters had adsorbed high CO2 amount, thatdetermined the decrease of pHT value ob-serveds. At the same time f CO2 values,calculated at the in situ temperature, rangedfrom 222.4 to 334.6 µatm from surfaceto the bottom over the whole area. Theyresulted much lower than the equilibriumvalue with atmospheric CO2 (398 µatm,mean value on measurements conducted onboard). This clearly indicated the occur-rence of under saturated conditions underwhich the northern Adriatic shelf region

was a potential sink for atmospheric CO2.Generally, NAdDW water mass flowssouthward and accumulates at the bottomof the Meso and Southern Adriatic pits(250 and 1250 m, respectively) [14] asevidenced in Figure 1 by density, higherthan 29.3 and 29.2 respectively, at the bot-tom. The dense waters of Meso Adri-atic pit exhibited pHT values lower (<7.880 pHT units) than those on the north-ern shelf because the water mass was older(AOU higher than 65.0 µM), remineralisa-tion processes had time to act releasing nu-trients and CO2 decreasing the pH, as in-dicated also by nutrients maxima (SiO2 >6.0 µM , DIN > 5.0 µM).In the southern part of the section, a veryclear event of deep convection was ob-

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served on February 2008 in the deepestcentral stations, as pointed out by the ho-mogeneous water column down to 600 m(σt around 29.15-29.16 kgm−3 down to600 m, in Figure 1). pHT had an aver-age value of 7.947 ± 0.003 pHT units,AOU was positive (15-35 µM) and nutri-ents were homogeneously distributed downto 600m. Such values suggest that the deepconvection allowed mixing between sur-face and older (AOU > 0) CO2 enricheddeep waters: for such reason surface AOUwere positive in contrast to what occurringalong the whole basin.These results are in agreement to whatreported in literature for the area, whichis known to be dominated by a quasi-permanent cyclonic circulation intensify-ing in autumn and creating the conditionsfor the production of dense and oxygenateddeep waters during winter deep convectionevents [14]. However f CO2 in situ values,around 370-380 µatm, were still slightlylower than the equilibrium value with at-mospheric CO2 (398 µatm). At the begin-ning of October ’08 the situation appearedcompletely changed as the whole Adriaticbasin was characterized by the thermal anddensity stratifications typical of late sum-mer conditions.In the northern shallow shelf region sea wa-ter temperature varied between 13.0 C to19.4 C from surface to bottom with an av-erage value of 17.6, 7.3 degrees higher thanFebruary. The upper water column wascharacterized by higher pHT values (be-tween 7.960 and 8.050 pHT units, Figure2) than in February, due to primary pro-duction process witnessed by the releaseof oxygen (negative AOU values) and thedepletion of all nutrients. In contrast, thelayer below pycnocline, was strongly de-pleted of oxygen (AOU mean value = 102.3µM), more acidic (7.784 pHT units) and

enriched in CO2 and nutrients (DIN upto 22.9 µM; f CO2>600 µatm) due to theremineralization of newly produced POCand labile DOC, all is characteristic of theautumn season.The bottom water mass in the Meso Adri-atic pit in October was about 0.1 °Ccolder than in February, less saline (0.1psu) and more oxigenated (DO 20 µmol/Lhigher), thus indicating at least the par-tial renewal of this water mass with theNAdDW formed during previous winter onthe northern shelf. Also in October pHT

mean value was low (7.861 pHT units,in Figure 2) and mainly determined byremineralization processes as evidenced byhigh AOU values (> 60 µM) and nutrientmaxima (DIN up to 7.0 µM, SiO2 up to 9.0µM).The southern part of the section wasalso characterized by late summer ther-mal and density stratifications (13.178 < T< 21.082 C), with the upper layer domi-nated by primary production processes (0< AOU < 15) and characterized by higherpHT (7.950 < pH < 8.0). In the layers be-low the pycnocline, remineralization pro-cesses prevailed as suggested by oxygenand nutrient values (AOU > 40 µM; DIN> 3.0 µM; SiO2 > 5.0 µM). Seasonal pri-mary production provides POC (in differ-ent amounts) to the euphotic layers, whichis available to the microbial community forremineralization during sinking to the bot-tom. This phenomenology was probably atthe basis of the pHT shift observed in thebottom water mass of the Southern Adri-atic pit between February (pHT = 7.937)and October (pHT = 7.898).This preliminary comparison between pHdistributions and oceanographic conditionsmet in February and October 2008 pointedout the high spatial and seasonal variabil-ity of pHT in the Adriatic sea. The fi-

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nal values were determined by the com-bined effects of circulation patterns, tem-perature driven CO2 solubility and biologi-cal processes (primary production, increas-ing pHT values, and respiration of organicmatter, lowering them).However the most significant conclusionwe can infer is the fact that the lower pHT

values of surface waters in winter were de-termined by the high dissolved CO2 con-centrations (due to atmospheric CO2 forc-ing). In contrast the drawdown of dissolvedCO2 by photosynthetic planktonic organ-isms led to higher pHT values in late sum-mer.

3.2 Long term variability ofpHT in the dense waters ofthe northern Adriatic Sea

The first comparison between two setsof data related to the dense cold waters(Northern Adriatic Dense Water) formed,respectively, in winters 1982-1983 and2007-2008 has been recently published[20]. Values of pH on the NBS scale fromthe old dataset were converted to the new”total hydrogen ion concentration scale”adopted for the new dataset and expressedin +/kgsw, as recommended by the inter-national scientific community. Some re-sults at 25 °C are summarized in Table 1,they show the decrease of both pHT aver-age value (-0.063 pH units) and carbonateion concentration (-19.6H+/kgsw), whichnamed OA. In contrast, the total alkalinity,dissolved inorganic carbon and CO2 fugac-ity exhibit net increases over the same pe-riod.

After an analysis of the different forc-ing (total alkalinity and dissolved carbondioxide) impacting on water masses dur-ing the two seasons and between the two

winters, the net increase of dissolved CO2

resulted to be the driving factor of theobserved inter-decadal acidification [20].This important result confirms that theAdriatic Sea is sensitive to atmospheric gassolubilisation (as CO2) and indicates thatOA has been affecting the Adriatic ma-rine waters for the last 25 years. It alsoindicates the need for a careful checking,in the coming decades, of the acidifica-tion rates as the impact on water quality,marine ecosystems and fishery resourcescould be not negligible. Although a deter-mination of acidification rates is not pos-sible on the base of only 2 specific yearsbecause interannual variations must alsobe considered, we inferred an approximate”acidification rate” over this time span. Itcorresponded to 0.0025 pH units/year, inagreement with acidification rates calcu-lated in other oceanic regions from timeseries: at ESTOC station in the openocean, Atlantic, Canary islands 0.0017 ±0.0004 pH units/year [21] 0.0012 ± 0.0004pH units/year, in the open Atlantic ocean,Bermuda Islands, [22].

3.3 Time series in the Gulf ofTrieste (northern AdriaticSea)

The acquisition of time series, at leastby a few key sites such as those wheredense water formation occurs in winter, isa promising strategy to monitor ocean acid-ification rates and impacts in the Mediter-ranean sea.On this concern, ISMAR Trieste has re-cently started the collection of pHT andother biogeochemical parameters time se-ries in the Gulf of Trieste (very shallow, thenorthernmost of the Mediterranean Sea),which is representative of a coastal envi-

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Param. Units N° samples

Average Std Dev Median

1983 pHT μmol/kgsw 33 8.010 ±.046 8.005

Tot. Alk μmol/kgsw 33 2584.5 ±10.9 2584.8 DIC μmol/kgsw 33 2256.3 ±32.1 2260.9 fCO2 μatm 33 485.1 ±63.6 489.2 H2CO3 μmol/kgsw 33 13.6 ±1.8 13.7 HCO3

- μmol/kgsw 33 2003.8 ±49.0 2011.1 CO3

= μmol/kgsw 33 239.0 ±19.5 236.1 Revelle 33 9.773 ±0.469 9.809 ΩCa 33 5.60 ±0.46 5.54 ΩAr 33 3.71 ±0.30 3.66

2008 pHT μmol/kgsw 56 7.946 ±0.012 7.947

Tot. Alk μmol/kgsw 61 2658.9 ±18.1 2658.1 DIC μmol/kgsw 54 2366.6 ±21.6 2370.3 fCO2 μatm 54 593.4 ±22.3 593.2 H2CO3 μmol/kgsw 54 16.6 ±0.6 16.6 HCO3

- μmol/kgsw 54 2130.6 ±23.9 2137.4 CO3

= μmol/kgsw 54 219.4 ±4.9 219.5 Revelle 54 10.491 ±0.168 10.493 ΩCa 54 5.14 ±0.11 5.14 ΩAr 54 3.40 ±0.07 3.40

Table 1: Values of the carbonate system parameters (at 25 °C) in the Northern AdriaticDense Water mass formed in winter 1983 and 2008.

ronment (Figure 3).Since January 2008, pHT , AT and themayor biogeochemical and physical pa-rameters were acquired on monthly basison the whole water column at the coastalsite PALOMA (centre of the Gulf, 25mdeep, close to the mast PALOMA - Ad-vanced Oceanic Laboratory PlatforM forthe Adriatic sea, 45° 37 N, 13° 34 E). Firstresults evidenced a complex time evolutionof pHT , mainly driven by the combined ef-fect of strong changes in both temperatureand production/ remineralisation processes

(Figure 3). During winter pHT values weregenerally low (7.868-7.958, avg 7.920) andhomogeneous owing to the increased CO2

solubility driven by the low water temper-ature (down to 8.0°C) and by the absenceof intense production processes. Duringspring and summer pHT was highly vari-able and mainly driven by the biologicalprocesses: the highest values (up to 8.120,June 2008) were reached in the upper layerduring high production events (AOU= -34µM) and the lowest values (down to 7.648,August 2008) in the bottom layer during

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Figure 3: Map of the sampling site PALOMA in the Gulf of Trieste; distribution ofmonthly values of pHT (a) and AOU (b) at PALOMA station from January 2008 to July2009.

biomass remineralisation (AOU= 142 µM).During Jan-March 2008 the oceanographicproperties (average σt = 29.35 kgm−3, T =8.84 °C) and pHT values (7.907 ± 0.028)of site PALOMA, indicating dense waterformation, fit well to the general NorthAdriatic Sea conditions over the same pe-riod. In summer, small scale biologicalprocesses prevailed in determining pHT

values both in PALOMA site and in theNorth Adriatic, depicting a more complexsituation.From such preliminary data, this site lo-cated in the centre of the Gulf of Triesteresults to be a good indicator not onlyof coastal dynamics/ processes but also ofsub-basin wide (North Adriatic Sea) pro-cesses and dynamics.

4 Impacts on biogeochem-istry and marine ecosys-tem

The most significant indication we candraw from the preliminary study onNAdDW is that the observed pH de-crease has affected the biogeochemistryof the carbonate system, causing specia-tion shifts (Table 1) as the decrease ofcarbonate ion concentration (from 236.1to 219.5 µ·mol · kg−1

sw ) accompanied bythe increases of bicarbonate ion and car-bonic acid concentrations (from 2011.1 to2137.4 µ·mol · kg−1

sw , from 13.7 to 16.6µ·mol · kg−1

sw , respectively) that fit well towhat generally observed in other oceanicregions [11]. Also the solubility ratios ofcalcite and aragonite show a decrease (ΩCa

from 5.51 to 5.14, ΩAr from 3.66 to 3.40)during last 25 years but, being far from1.0, they indicate that NAdDW is still over-saturated with respect to calcium carbon-

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ate, as already observed for the Mediter-ranean Sea [6]. Therefore, the AdriaticSea with its adequate carbonate saturationsstate seems to ensure still quite healthygrowth conditions for calcifying organisms(from plankton to benthic molluscs, echin-oderms and corals). The increase of theRevelle factor in the same period (R= 9.773± 0.469 and 10.491 ± 0.168, respectively)suggest a decrease of the buffering capac-ity of the whole carbonate system [23]).There are several impacts of OA on the ma-rine ecosystem which have not yet been in-vestigated. For example the observed pHdecrease might have impacted the carbonfixation capacity by photosynthetic organ-isms (calcifyer and non calcifyer), actuallya few papers report the possibility of anincrease of primary productivity [4] in re-sponse to ocean acidification. An increaseof primary production might further affecthypoxia and anoxia events, already sea-sonally occurring in the northern Adriaticbasin [24], through an increase of the mi-crobial respiration of the surplus of organicmatter. On another hand, the combinedimpacts of increased stratification, due tothe global warming, and changes in theocean biology, caused by ocean acidifica-tion, could cause a further decline in dis-solved oxygen concentrations as recentlyforecast by Oeschlies [25]. If this wouldoccur in the North Adriatic it might exac-erbate hypoxia and anoxia. Another sig-nificant impact of OA in the North Adriaticcould be represented by the increase of dis-

solved organic carbon (DOC) productionas response to the increase of primary pro-duction induced by OA [26]. If the DOCincrease would be assessed true also for theAdriatic Sea, it might have major effectson mucillages phenomena which affect thebasin, as mucillages are aggregates of mu-chopolysaccharide and would be favouredby higher DOC concentrations.In the end, all these aspects could havemassive consequences on marine resources(fishery, aquaculture, tourism). Hence theNorthern Adriatic Sea offers challengesfor future research activities of high pri-ority. Thus confirming to be an interest-ing basin where assessing the impacts ofOcean Acidification with the potential formarine organisms to adapt to increasingCO2, and broader implications for marineecosystems.

5 AcknowledgementThe authors thank: dr. Massimo Celio(ARPA-FVG) for the use of CTD data ac-quired at PALOMA station and dr. Ve-drana Kovacevic (OGS-Trieste) for the useof CTD data acquired during VECTORand SESAME campaigns. They are grate-ful to the captains and crews of R/V Ura-nia (CNR) and Effevigi (ARPA-FVG). Thestudy was funded by the VECTOR projectof the Italian Ministry for University andScientific Research and by the SESAMEproject of the European Commission.

References[1] D. Luthi, M. Le Floch, B. Bereiter, T. Blunier, J.M. Barnola, et al. High-resolution

carbon dioxide concentration record 650,000-800,000 years before present. Nature,453:379–382, 2008.

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[2] C.L. Sabine, R.A. Feely, R.M. Gruber, N.and Key, and K. Lee et al. The oceanicsink for anthropogenic CO2. Science, 305:367–371, 2004.

[3] C.L. Sabine and R.A. Feely. The oceanic sink for carbon dioxide. In: Greenhousegas sink, D. Ready, N. Hewitt, J. Grace and K. Smith (editors). pages 31–49, 2007.

[4] S.C. Doney, V.J. Fabry, R.A. Feely, and J. A Kleypas. Ocean Acidification: TheOther CO2 Problem. Annual. Reviews Marine Science, 1:169–192, 2009.

[5] K. Caldeira and M.E. Wickett. Anthropogenic carbon and ocean pH. Nature,425:365–365, 2003.

[6] A. Schneider, D.W.R. Wallace, and A. Koertzinger. Alkalinity of the MediterranenaSea. Geophys. Res. Letters, 34(L15608), 2007.

[7] R.A. Feely, C.L. Sabine, K. Lee, W. Berelson, J. Kleypas, et al. Impact of anthro-pogenic CO2 on the CaCO3 system in the oceans. Science, 305:362–366, 2004.

[8] R.A. Feely, J. Orr, V.J. Fabry, J.A. Kleypas, C.L. Sabine, and C. Langdon. Presentand future changes in seawater chemistry due to ocean acidifcation. In: Carbonsequestration and its role in the global carbon cycle, Brian J. McPherson and EricT. Sundquist (eds.). AGU Monograph, 2009.

[9] J.C. Orr, V.J. Fabry, O. Aumont, L. Bopp, S.C. Doney, R. A. Feely, A. Gnanade-sikan, N. Gruber, A. Ishida, F. Joos, R.M. Key, K. Linsay, E.M. Reimer, R. Matear,P. Monfray, A. Mouchet, R.G. Najjar, G.K. Plattner, K.B. Rodgers, C.L. Sabine,J.L. Sarmiento, R. Schlitzer, R.D. Slater, I.J. Totterdell, M.F. Weirig, Y. Yamanaka,and A. Yool. Anthropogenic ocean acidification over the twenty-first century andits impact on calcifying organisms. Nature, 437:681–686, 2005.

[10] S. Solomon, D. Quin, and M. Mannings et al. Climate Change 2007: the physicalscience basis: contribution of working group I to the Fourth Assessment Report ofthe Intergovernamental Panel on Climate change. New York (2007). CambridgeUniv. Press, 2007.

[11] Royal Society. Ocean acidification due to increasing carbon dioxide, Policy Docu-ment 12/05. 2005.

[12] A. Yilmaz et al. Impacts of acidification on biological, chemical and physical sys-tems in the Mediterranean and Black Seas. In: CIESM Workshop Monographs N°36. F. Briand editor, CIESM, Monaco. page 124, 2008.

[13] MEDAR Group. MEDATLAS/2002 database. Mediterranean and Black Seadatabase of temperature salinity and bio-chemical parameters. Climatological At-las. IFREMER Edition (4 Cd). 2002.

1253

Oceanography

[14] M. Gacic, A. Lascaratos, B.B. Manca, and A. Mantziafoul. Adriatic deep waterand interaction with the eastern Mediterranean Sea. In: Physical Ocenaography ofthe Adriatic Sea. Past, Present and Future. In: B. Cushman-Roisin, M. Gacic, M.P.Poulain and A. Artegiani (eds.), Kluwer Academic Publishers, The Netherlands.pages 111–142, 2001.

[15] W. Roether, B. Manca, B. Klein, D. Bregant, D. Georgopoulos, V. Beitzel, V. Ko-vacevic, and A. Luchetta. Recent changes in the Eastern Mediterranean deep wa-ters. Science, 271:333–335, 1996.

[16] A.G. Dickson, C.L. Sabine, and J.R Christian. Guide to best practices for oceanCO2 measurements. PICES Special Publication, 3:191, 2007.

[17] E. Lewis and D.W.R. Wallace. Program Developed for CO2 System Calculations.ORNL/CDIAC-105. Carbon Dioxide Information Analysis Centre, Oak Ridge Na-tional Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee. 1998.

[18] P. Malanotte-Rizzoli. The northern Adriatic Sea as a prototype of convection andwater mass formation on the continental shelf. In: Deep convection and deep waterformation in the oceans. P.C. Chu and J.C. Gascard (eds.). Elsevier OceanographySeries, 57:229–239, 1991.

[19] A. Artegiani, E. Paschini, A. Russo, D. Bregant, F. Raicich, and N. Pinardi. TheAdriatic Sea Circulation, Part 1: Air-sea interactions and water mass structure. J.Phys. Oceanography, 27:1492–1515, 1997.

[20] A. Luchetta, C. Cantoni, and G. Catalano. New observations of CO2 induced acid-ification in the Northern Adriatiic Sea, over the last quarter century. Chemistry andEcology, 26:1–17, 2010.

[21] J.M. et al. Santana Casiano. The interannual variability of oceanic CO2 in thenortheast Atlantic subtropical gyre at the ESTOC site. Global Biogeochem. Cycles,21(GB1015), 2007.

[22] N.R. Bates. Interannual variability of CO2 sink in the subtropical gyre of the NorthAtlantic Ocean over the last two decades. J. Geophys. Res., 112, 2007.

[23] F.J. Millero. The marine inorganic carbon cycle. Chemical Reviews, 107:308–341,2007.

[24] R. Marchetti. The problems of the Emilia Romagna coastal waters: facts and inter-pretations. In: Marine Coastal Eutrophication. pages 21–33, 1992.

[25] A. Oschlies, K.G. Schulz, U. Riebesell, and A. Schmittner. Simulated 21st cen-tury’s increase in oceanic suboxia by CO2-enhanced biotic carbon export. GlobalBiogeochemical Cycles, 22, 2008.

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[26] U. Riebesell, K. G. Schulz, R. G. J. Bellerby, M. Botros, P. Fritsche, Meyerhofer,et al. Enhanced biological carbon consumption in a high CO2 ocean. Nature,450:545–548, 2007.

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