References

Biogeosciences

1726-4189

Copernicus Publications

Göttingen, Germany

10.5194/bg-12-1387-2015

Rapid acidification of mode and intermediate waters in the southwestern Atlantic Ocean

Salt

L. A.

¹ ⁵ van Heuven

S. M. A. C.

https://orcid.org/0000-0003-2001-8710

² ⁶ Claus

M. E.

³ Jones

E. M.

⁴ de Baar

H. J. W.

¹ ³

Royal Netherlands Institute for Sea Research, Landsdiep 4, 1797 SZ, Texel, the Netherlands

Centre for Isotope Research, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, the Netherlands

Department of Ocean Ecosystems, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, the Netherlands

Alfred Wegener Institute for Polar and Marine Research, 120161, 27515, Bremerhaven, Germany

now at: CNRS, UMR7144, Equipe Chimie Marine, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France

now at: Alfred Wegner Institute, Climate Sciences Department, Postfach 120161, 27515 Bremerhaven, Germany

05 03 2015

12 5 1387 1401

2015

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

This article is available from https://bg.copernicus.org/articles/12/1387/2015/bg-12-1387-2015.html

The full text article is available as a PDF file from https://bg.copernicus.org/articles/12/1387/2015/bg-12-1387-2015.pdf

Observations along the southwestern Atlantic WOCE A17 line made during the Dutch GEOTRACES-NL programme (2010–2011) were compared with historical data from 1994 to quantify the changes in the anthropogenic component of the total pool of dissolved inorganic carbon (ΔCant). Application of the extended multi-linear regression (eMLR) method shows that the ΔCant from 1994 to 2011 has largely remained confined to the upper 1000 dbar. The greatest changes occur in the upper 200 dbar in the Subantarctic Zone (SAZ), where a maximum increase of 37 μmol kg−1 is found. South Atlantic Central Water (SACW) experienced the highest rate of increase in Cant, at 0.99 ± 0.14 μmol kg−1 yr−1, resulting in a maximum rate of decrease in pH of 0.0016 yr−1. The highest rates of acidification relative to ΔCant, however, were found in Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). The low buffering capacity of SAMW and AAIW combined with their relatively high rates of Cant, increase of 0.53 ± 0.11 and 0.36 ± 0.06 μmol kg−1 yr−1, respectively, has lead to rapid acidification in the SAZ, and will continue to do so whilst simultaneously reducing the chemical buffering capacity of this significant CO2 sink.

References 1

Álvarez, M., Lo Monaco, C., Tanhua, T., Yool, A., Oschlies, A., Bullister, J. L., Goyet, C., Metzl, N., Touratier, F., McDonagh, E., and Bryden, H. L.: Estimating the storage of anthropogenic carbon in the subtropical Indian Ocean: a comparison of five different approaches, Biogeosciences, 6, 681–703, <a href="http://dx.doi.org/10.5194/bg-6-681-2009">https://doi.org/10.5194/bg-6-681-2009</a>, 2009.

Álvarez, M., Tanhua, T., Brix, H., Lo Monaco, C., Metzl, N., McDonagh, E. L., and Bryden H. L.: Decadal biogeochemical changes in the subtropical Indian Ocean associated with Subantarctic Mode Water, J. Geophys. Res., 116, C09016, <a href="http://dx.doi.org/10.1029/2010JC006475">https://doi.org/10.1029/2010JC006475</a>, 2011.

Álvarez, M., Sanleón-Bartolomé, H., Tanhua, T., Mintrop, L., Luchetta, A., Cantoni, C., Schroeder, K., and Civitarese, G.: The CO2 system in the Mediterranean Sea: a basin wide perspective, Ocean Sci., 10, 69–92, <a href="http://dx.doi.org/10.5194/os-10-69-2014">https://doi.org/10.5194/os-10-69-2014</a>, 2014.

Bednarsek, N., Tarling, G. A., Bakker, D. C. E., Fielding, S., Jones, E. M., Venables, H. J., Ward, P., Kuzirian, A., Lézé, B., Feely, R. A., and Murphy, E. J.: Extensive dissolution of live pteropods in the Southern Ocean, Nat. Geosci., 5, 881–885, <a href="http://dx.doi.org/10.1038/NGEO1635">https://doi.org/10.1038/NGEO1635</a>, 2012.

Bindoff, N. L., Willebrand, J., Artale, V., Cazenave, A., Gregory, J., Gulev, S., Hanawa, K., Le Quéré, C., Levitus, S., Nojiri, Y., Shum, C. K., Talley, L. D., and Unnikrishnan, A.: Observations: Oceanic Climate Change and Sea Level, in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K. B., Tignor, M., and Miller, H. L., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 385–432, 2007.

Brewer, P. G.: Direct observation of the oceanic CO2 increase, Geophys. Res. Lett., 5, 997–1000, 1978.

Brown, P. J., Bakker, D. C. E., Schuster, U., and Watson, A. J.: Anthropogenic carbon accumulation in the subtropical North Atlantic, J. Geophys. Res., 115, C04016, <a href="http://dx.doi.org/10.1029/2008JC005043">https://doi.org/10.1029/2008JC005043</a>, 2010.

CARINA Group: Carbon in the Atlantic Ocean Region – the CARINA project: Results and Data, Version 1.0., Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee. <a href="http://dx.doi.org/10.3334/CDIAC/otg.CARINA.ATL.V1.0">https://doi.org/10.3334/CDIAC/otg.CARINA.ATL.V1.0</a>, 2009.

Dickson, A. G.: Standard potential of the reaction: AgCl(s) + 1/2H2(g) = Ag(s) + HCl(aq), and the standard acidity constant of the ion HSO4- in synthetic seawater from 273.15 to 318.15 K, J. Chem. Thermodyn., 22, 113–127, 1990.

Dickson, A. G. and Millero, F. J.: A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media, Deep Sea Res., 34, 1733–1743, 1987.

Dickson, A. G., Sabine, C. L., and Christian, J. R. (Eds.): Guide to best practices for ocean CO2 measurements, PICES Special Publications 3, 191 pp., <a href="http://dx.doi.org/10.1029/2006JC004051">https://doi.org/10.1029/2006JC004051</a>, 2007.

Egleston, E. S., Sabine, C. L., and Morel, M.: Revelle revisited: Buffer factors that quantify the reponse of ocean chemistry to changes in DIC and alkalinity, Global Biogeochem. Cy., 24, GB1002, <a href="http://dx.doi.org/10.1029/2008GB003407">https://doi.org/10.1029/2008GB003407</a>, 2010.

Friis, K., Körtzinger, A., Patsch, J., and Wallace, D. W. R.: On the temporal increase of anthropogenic CO2 in the subpolar North Atlantic, Deep-Sea Res. Pt. I, 52, 681–698, <a href="http://dx.doi.org/10.1016/j.dsr.2004.11.017">https://doi.org/10.1016/j.dsr.2004.11.017</a>, 2005.

González-Dávila, M., Santana-Casiano, J. M., Fine, R. A., Happell, J., Delille, B., and Speich, S.: Carbonate system in the water masses of the Southeast Atlantic sector of the Southern Ocean during February and March 2008, Biogeosciences, 8, 1401–1413, <a href="http://dx.doi.org/10.5194/bg-8-1401-2011">https://doi.org/10.5194/bg-8-1401-2011</a>, 2011.

Grasshof, K., Ehrhardt, M., and Kremling, K.: Methods of seawater analysis, Verlag Chemie GmbH, Weinheim, 125–188, 1983.

Gruber, N., Sarmiento, J. L., and Stocker, T. F.: An improved method for detecting anthropogenic CO2 in the oceans, Global Biogeochem. Cy., 10, 809–837, 1996.

Hartin, C. A., Fine, R. A., Sloyan, B. M., Talley, L. D., Chereskin, T. K., and Happell, J.: Formation rates of Subantarctic mode water and Antarctic intermediate water within the South Pacific, Deep-Sea Res. Pt. I, 158, 524–534, 2011.

Hauck, J., Hoppema, M., Bellerby, R. G. J., Völker, C., and Wolf-Gladrow, D.: Data-based estimation of anthropogenic carbon and acidification in the Weddell Sea on a decadal timescale, J. Geophys. Res., 115, C03004, <a href="http://dx.doi.org/10.1029/2009JC005479">https://doi.org/10.1029/2009JC005479</a>, 2010.

Johnson, K. M., Sieburth, J. M., Williams, P. J., and Brändström, L.: Coulometric total carbon dioxide analysis for marine studies: Automation and calibration, Mar. Chem., 21, 117–133, 1987.

Karstensen, J. and Quadfasel, D.: Water subducted into the Indian Ocean subtropical gyre, Deep Sea-Res.-Pt. II, 49, 1441–1457, 2002.

Key, R. M., Tanhua, T., Olsen, A., Hoppema, M., Jutterström, S., Schirnick, C., van Heuven, S., Kozyr, A., Lin, X., Velo, A., Wallace, D. W. R., and Mintrop, L.: The CARINA data synthesis project: introduction and overview, Earth Syst. Sci. Data, 2, 105–121, <a href="http://dx.doi.org/10.5194/essd-2-105-2010">https://doi.org/10.5194/essd-2-105-2010</a>, 2010.

Lee, K., Choi, S.-D., Park, G.-H., Wanninkhof, R., Peng, T.-H., Key, R. M., Sabine, C. L., Feely, R. A., Bullister, J. L., Millero, F. J., and Kozyr, A.: An updated anthropogenic CO2 inventory in the Atlantic Ocean, Global Biogeochem. Cy., 17, 1116, <a href="http://dx.doi.org/10.1029/2003GB002067">https://doi.org/10.1029/2003GB002067</a>, 2003.

Levine, N. M., Doney, S. C., Wanninkhof, R., Lindsay, K., and Fung, I. Y.: Impact of ocean carbon system variability on the detection of temporal increases in anthropogenic CO2, J. Geophys. Res., 113, C03019, <a href="http://dx.doi.org/10.1029/2007JC004153">https://doi.org/10.1029/2007JC004153</a>, 2008.

Lewis, E. L. and Wallace, D. W. R.: Program developed for CO2 system calculations, ORNL/CDIAC-105, Carbon dioxide information analysis center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, 1998.

Lischka, S., Büdenbender, J., Boxhammer, T., and Riebesell, U.: Impact of ocean acidification and elevated temperatures on early juveniles o f the polar shelled pteropod Limacina helicina: mortality, shell degradation, and shell growth, Biogeosciences, 8, 919–932, <a href="http://dx.doi.org/10.5194/bg-8-919-2011">https://doi.org/10.5194/bg-8-919-2011</a>, 2011.

Lovenduski, N. S., Gruber, N., Doney, S. C., and Lima, I. D.: Enhanced CO2 outgassing in the Southern Ocean from a positive phase of the Southern Annular Mode, Global Biogeochem. Cy., 21, GB2026, <a href="http://dx.doi.org/10.1029/2006GB002900">https://doi.org/10.1029/2006GB002900</a>, 2007.

McCartney, M. S.: Subantarctic Mode Water, in: A Voyage of Discovery, edited by: Angel, M., Pergamon, Elmsford, New York, 103–119, 1977.

McNeil, B. I. and Matear, R. J.: Southern Ocean acidification: A tipping point at 450 ppm atmospheric CO2, P. Natl. Acad. Sci., 105, 18860–18864, 2008.

McNeil, B. I., Tilbrook, B., and Matear, R.: Accumulation and uptake of anthropogenic CO2 in the Southern Ocean, south of Australia between 1968 and 1996, J. Geophys. Res., 106, 31431–31445, 2001.

McNeil, B. I., Metzl, N., Key, R. M., Matear, R. J., and Corbiere, A.: An empirical estimate of the Southern Ocean air-sea CO2 flux, Global. Biogeochem. Cy., 21, GB3011, <a href="http://dx.doi.org/10.1029/2007GB002991">https://doi.org/10.1029/2007GB002991</a>, 2007.

Mehrbach, C., Culberson, C. H., Hawley, J. E., and Pytkowicz, R. M.: Measurement of the apparent dissociation constants of carbonic acid in seawater at atmospheric pressure, Limnol. Oceanogr., 18, 897–907, 1973.

Mémery, L., Arhan, M., Alvarez-Salgado, X. A., Messias, M.-J., Mercier, H., Castro, C. G., and Ríos, A. F.: The water masses along the western boundary of the south and equatorial Atlantic, Prog. Oceanogr., 47, 69–98, 2000.

Metzl, N., Tilbrook, B., and Poisson, A.: The annual fCO2 cycle and the air-sea CO2 flux in the sub-Antarctic Ocean, Tellus, 51B, 849–861, 1999.

Mintrop, L., Perez, F. F., Gonzalez-Davila, M., Santana-Casiano, M. J., and Kortzinger, A.: Alkalinity determination by potentiometry: intercalibration using three different methods, Cienc. Marinas, 26, 23–37, 2000.

Murata, A., Kumamoto, Y., Sasaki, K.'I., Watanabe, S., and Fukasawa, M.: Decadal increases of anthropogenic CO2 in the subtropical South Atlantic Ocean along 30° S, J. Geophys. Res., 113, C06007, <a href="http://dx.doi.org/10.1029/2007JC004424">https://doi.org/10.1029/2007JC004424</a>, 2008.

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

Orsi, A. H., Johnson, G. C., and Bullister, J. L.: Circulation, mixing, and production of Antarctic Bottom Water, Prog. Oceanogr., 43, 55–109, 1999.

Peng, T.-H. and Wanninkhof, R.: Increase in anthropogenic CO2 in the Atlantic Ocean in the last two decades, Deep-Sea Res. Pt. I, 57, 755–770, <a href="http://dx.doi.org/10.1016/j.dsr.2010.03.008">https://doi.org/10.1016/j.dsr.2010.03.008</a>, 2010.

Pérez, F. F., Álvarez, M., and Ríos, A. F.: Improvements on the back-calculation technique for estimating anthropogenic CO2, Deep-Sea Res. Pt. I, 49, 859–875, 2002.

Pérez, F. F., Vázquez-Rodríguez, M., Mercier, H., Velo, A., Lherminier, P., and Ríos, A. F.: Trends of anthropogenic CO2 storage in North Atlantic water masses, Biogeosciences, 7, 1789–1807, <a href="http://dx.doi.org/10.5194/bg-7-1789-2010">https://doi.org/10.5194/bg-7-1789-2010</a>, 2010.

Peterson, R. G. and Whitworth, T.: The Subantarctic and Polar Fronts in relation to deep water masses through the Southwestern Atlantic, J. Geophys. Res., 94, 10817–10838, 1989.

Revelle, R. and Suess, H.: Carbon dioxide exchange between atmosphere and ocean and the question of an increase of atmospheric CO2 during the past decades, Tellus, 9, 18–27, 1957.

Ríos, A. F., Johnson, K. M., Alvarez-Salgado, X. A., Arlen, L., Billant, A., Bingler, L. S., Branellec, P., Castro, C. G., Chipman, D. W., Roson, G., and Wallace, D. W. R.: Carbon Dioxide, Hydrographic, and Chemical Data Obtained During the R/V Maurice Ewing Cruise in the South Atlantic Ocean (WOCE Section A17, 4 Janurary–21 March 1994), Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, ORNL/CDIAC-148, NDP-084, 1–27, 2005.

Ríos, A. F., Vázquez-Rodríguez, M., Padin, X. A., and Pérez, F. F.: Anthropogenic carbon dioxide in the South Atlantic western basin, J. Mar. Syst., 83, 38–44, 2010.

Ríos, A. F., Velo, A., Pardo, P. C., Hoppema, M., and Pérez, F.F.: An update of anthropogenic CO2 storage rates in the western South Atlantic basin and the role of Antarctic Bottom Water, J. Mar. Syst., 94, 197–203, <a href="http://dx.doi.org/10.1016/j.jmarsys.2011.11.023">https://doi.org/10.1016/j.jmarsys.2011.11.023</a>, 2012.

Sabine, C. L. and Tanhua, T.: Estimation of Anthropogenic CO2 Inventories in the Ocean, Ann. Rev. Mar. Sci., 2, 175–198, <a href="http://dx.doi.org/10.1146/annurev-marine-120308-080947">https://doi.org/10.1146/annurev-marine-120308-080947</a>, 2010.

Sabine, C. L., Key, R. M., Johnson, K. M., Millero, F. J., Poisson, A., Sarmiento, J. L., Wallace, D. W. R., and Winn, C. D.: Anthropogenic CO2 inventory of the Indian Ocean, Global Biogeochem. Cy., 13, 179–198, 1999.

Sabine, C. L., Feely, R. A., Gruber, N., Key, R. M., Lee, K., Bullister, J. L., Wanninkhof, R., Wong, C. S., Wallace, D. W. R., Tilbrook, B., Millero, F. J., Peng, T.-H., Kozyr, A., Ono, T., and Rios, A. F.: The Oceanic Sink for Anthropogenic CO2, Science, 305, 367–371, 2004.

Santana-Casiano, J. M., González-Dávila, M., Rueda, M.-J., Llinás, O., and González-Dávila, E.-F.: The interannual variability of oceanic CO2 parameters in the northeast Atlantic subtropical gyre at the ESTOC site, Global Biogeochem. Cy., 21, GB1015, <a href="http://dx.doi.org/10.1029/2006GB002788">https://doi.org/10.1029/2006GB002788</a>, 2007.

Sarmiento, J. L., Gruber, N., Brzezinski, M. A., and Dunne, J. P.: High-latitude controls of thermocline nutrients and low latitude, Nature, 427, 56–60, 2004.

Schneider, A., Tanhua, T., Kortzinger, A., and Wallace, D. W. R.: An evaluation of tracer fields and anthropogenic carbon in the equatorial and the tropical North Atlantic, Deep-Sea Res. Pt. I, 67, 85–97, 2012.

Talley, L. D.: Antarctic intermediate water in the South Atlantic, edited by: Wefer, G., Berger, H. H., Siedler, G., and Webb, D., in: The South Atlantic: Present and Past Circulation, Springer-Verlag, 219–238, 1996.

Tanhua, T.: Matlab Toolbox to Perform Secondary Quality Control (2nd QC) on Hydrographic Data, ORNL/CDIAC-158, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, <a href="http://dx.doi.org/10.3334/CDIAC/otg.CDIAC_158">https://doi.org/10.3334/CDIAC/otg.CDIAC_158</a>, 2010.

Touratier, F., Azouzi, L., and Goyet, C.: CFC-11, Δ14C and 3H tracers as a means to assess anthropogenic CO2 concentrations in the ocean, Tellus, 59B, 318–325, 2007.

van Heuven, S., Pierrot, D., Lewis, E., and Wallace, D. W. R.: MATLAB Program Developed for CO2 System Calculations, ORNL/CDIAC-105b, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, 2011a.

van Heuven, S. M. A. C., Hoppema, M., Huhn, O., Slagter, H. A., and de Baar, H. J. W.: Direct observation of increasing CO2 in the Weddell Gyre along the Prime Meridian during 1973–2008, Deep-Sea Res. Pt. II, 58, 2613–2635, <a href="http://dx.doi.org/10.1016/j.dsr2.2011.08.007">https://doi.org/10.1016/j.dsr2.2011.08.007</a>, 2011b.

Vázquez-Rodríguez, M.: Reconstructing preformed properties and air-sea CO2 disequilibria for water masses in the Atlantic from subsurface data: An application in anthropogenic carbon determination, PhD Thesis of University of Vigo, Spain, 48–60, 2008.

Vázquez-Rodríguez, M., Touratier, F., Lo Monaco, C., Waugh, D. W., Padin, X. A., Bellerby, R. G. J., Goyet, C., Metzl, N., Ríos, A. F., and Pérez, F. F.: Anthropogenic carbon distributions in the Atlantic Ocean: data-based estimates from the Arctic to the Antarctic, Biogeosciences, 6, 439–451, <a href="http://dx.doi.org/10.5194/bg-6-439-2009">https://doi.org/10.5194/bg-6-439-2009</a>, 2009a.

Vázquez-Rodríguez, M., Padin, X. A., Ríos, A. F., Bellerby, R. G. J., and Pérez, F. F.: An upgraded carbon-based method to estimate the anthropogenic fraction of dissolved CO2 in the Atlantic Ocean, Biogeosciences Discuss., 6, 4527–4571, <a href="http://dx.doi.org/10.5194/bgd-6-4527-2009">https://doi.org/10.5194/bgd-6-4527-2009</a>, 2009b.

Vázquez-Rodríguez, M., Pérez, F. F., Velo, A., Ríos, A. F., and Mercier, H.: Observed acidification trends in North Atlantic water masses, Biogeosciences, 9, 5217–5230, <a href="http://dx.doi.org/10.5194/bg-9-5217-2012">https://doi.org/10.5194/bg-9-5217-2012</a>, 2012.

Wallace, D. W. R.: Monitoring global ocean carbon inventories. OOSDP Background Report No. 5, Texas A&M University, College Station, Texas, USA, 54 pp., 1995.

Wanninkhof, R., Doney, S. C., Bullister, J. L., Levine, N. M., Warner, M., and Gruber, N.: Detecting anthropogenic CO2 changes in the interior Atlantic Ocean between 1989 and 2005, J. Geophys. Res., 115, C11028, <a href="http://dx.doi.org/10.1029/2010JC006251">https://doi.org/10.1029/2010JC006251</a>, 2010.

Waugh, D. W., Hall, T. M., McNeil, B. I., Key, R., and Matear, R. J.: Anthropogenic CO2 in the oceans estimated using transit time distributions, Tellus, 58B, 376–389, <a href="http://dx.doi.org/10.1111/j.1600-0889.2006.00222.x">https://doi.org/10.1111/j.1600-0889.2006.00222.x</a>, 2006.

Wong, A. P. S., Bindoff, N. L., and Church, J. A.: Large-scale freshening of intermediate waters in the Pacific and Indian oceans, Nature, 400, 440–443, 1999.

Yool, A., Oschlies, A., Nurser, A. J. G., and Gruber, N.: A model-based assessment of the TrOCA approach for estimating anthropogenic carbon in the ocean, Biogeosciences, 7, 723–751, <a href="http://dx.doi.org/10.5194/bg-7-723-2010">https://doi.org/10.5194/bg-7-723-2010</a>, 2010.