Abstract
Large-scale features of ocean circulation, such as deep water formation in the northern North Atlantic Ocean1, are known to regulate the long-term physical uptake of CO2 from the atmosphere by moving CO2-laden surface waters into the deep ocean. But the importance of CO2 uptake into water masses that ventilate shallower ocean depths, such as subtropical mode waters2 of the subtropical gyres, are poorly quantified. Here we report that, between 1988 and 2001, dissolved CO2 concentrations in subtropical mode waters of the North Atlantic have increased at a rate twice that expected from these waters keeping in equilibrium with increasing atmospheric CO2. This accounts for an extra ∼0.4–2.8 Pg C (1 Pg = 1015 g) over this period (that is, about 0.03–0.24 Pg C yr-1), equivalent to ∼3–10% of the current net annual ocean uptake of CO2 (ref. 3). We suggest that the lack of strong winter mixing events, to greater than 300 m in depth, in recent decades is responsible for this accumulation, which would otherwise disturb the mode water layer and liberate accumulated CO2 back to the atmosphere. However, future climate variability (which influences subtropical mode water formation1,4,5,6,7,8) and changes in the North Atlantic Oscillation9 (leading to a return of deep winter mixing events) may reduce CO2 accumulation in subtropical mode waters. We therefore conclude that, although CO2 uptake by subtropical mode waters in the North Atlantic—and possibly elsewhere—does not always represent a long-term CO2 sink, the phenomenon is likely to contribute substantially to interannual variability in oceanic CO2 uptake3.
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References
Dickson, R., Lazier, J., Meincke, J., Rhines, P. & Swift, J. Long-term coordinated changes in the convective activity of the North Atlantic. Prog. Oceanogr. 38, 241–295 (1996)
Hanawa, K. & Talley, L. D. Ocean Circulation and Climate International Geophysics Series (eds Siedler, G., Church, J. & Gould, J.) Vol. 77, 378–386 (Academic, San Diego, 2001)
Prentice, C. et al. Climate Change 2001: The Scientific Basis (eds Houghton, J. T. et al.) 183–237 (Cambridge Univ. Press, Cambridge, 2001)
Klein, B. & Hogg, N. On the interannual variability of 18 degree water formation as observed from moored instruments at 55°W. Deep-Sea Res. 43, 1777–1806 (1996)
Hazeleger, W. & Drijfhout, S. S. Mode water variability in a model of the subtropical gyre: response to anomalous forcing. J. Phys. Oceanogr. 28, 266–288 (1998)
Joyce, T. M., Deser, C. & Spall, M. A. The relation between decadal variability of subtropical mode water and the North Atlantic Oscillation. J. Clim. 13, 2550–2569 (2000)
Alfutis, M. A. & Cornillon, P. Annual and interannual changes in the North Atlantic STMW layer properties. J. Phys. Oceanogr. 31, 2066–2086 (2001)
Rodwell, M. J., Rowell, D. P. & Folland, C. K. Oceanic forcing of the wintertime North Atlantic Oscillation and European climate. Nature 398, 320–323 (1999)
Hurrell, J. W. Decadal trends in the North Atlantic Oscillation: regional temperatures and precipitation. Science 269, 676–679 (1995)
Worthington, L. V. The 18° water in the Sargasso Sea. Deep-Sea Res. 5, 297–305 (1959)
Jenkins, W. J. Studying subtropical thermocline ventilation and circulation using tritium and 3He. J. Geophys. Res. 103, 15817–15831 (1998)
Talley, L. & Raymer, M. Eighteen degree water variability. J. Mar. Res. 40 (suppl.), 757–775 (1982)
Jenkins, W. G. On the climate of the subtropical gyre: Decade timescale variation in water mass renewal in the Sargasso Sea. J. Mar. Res. 40 (suppl.), 265–290 (1982)
Joyce, T. M. & Robbins, P. The long-term hydrographic record at Bermuda. J. Clim. 9, 3121–3131 (1996)
Bates, N. R. Interannual changes of oceanic CO2 and biogeochemical properties in the Western North Atlantic subtropical gyre. Deep-Sea Res. II 48, 1507–1528 (2001)
Bates, N. R., Michaels, A. F. & Knap, A. H. Seasonal and interannual variability of the oceanic carbon dioxide system at the U.S. JGOFS Bermuda Atlantic Time-series Site. Deep-Sea Res. II 43, 347–383 (1996)
Keeling, C. D. The Global Carbon Cycle (ed. Heimann, M.) 413–430 (Springer, New York, 1993)
Karl, D. M. et al. Temporal studies of biogeochemical processes in the world's oceans during the JGOFS era. Deep-Sea Res. (in the press)
Gruber, N. & Sarmiento, J. L. The Sea: Biological-Physical Interactions in the Ocean (eds Robinson, A. R., McCarthy, J. J. & Rothschild, B. J.) Vol. 12, 337–399 (Wiley and Sons, New York, 2002)
Conte, M. H., Ralph, N. & Ross, E. H. Seasonal and interannual variability in deep ocean particle fluxes at the Ocean Flux Program (OFP)/Bermuda Atlantic Time-series Study (BATS) site in the western Sargasso Sea near Bermuda. Deep-Sea Res. II 48, 1471–1507 (2001)
Wanninkhof, R. & McGillis, W. R. A cubic relationship between air-sea CO2 exchange and wind speed. Geophys. Res. Lett. 26, 1889–1892 (1999)
Takahashi, T. et al. Global air-sea flux of CO2 based on surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II 49, 1601–1622 (2002)
Behringer, D. & Stommel, H. The beta-spiral in the North Atlantic subtropical gyre. Deep-Sea Res. A 27, 225–238 (1980)
Spall, M. A. Cooling spirals and recirculation in the subtropical gyre. J. Phys. Oceanogr. 22, 564–571 (1992)
Woods, J. D. & Barkmann, W. A lagrangian mixed layer model of Atlantic 18° water formation. Nature 319, 574–576 (1986)
Speer, K. & Tziperman, E. Rates of water mass formation in the North Atlantic Ocean. J. Phys. Oceanogr. 22, 93–104 (1992)
Marsh, R. & New, A. L. Modeling 18° water variability. J. Phys. Oceanogr. 26, 1059–1080 (1996)
Luyten, J. R., Pedlosky, J. & Stommel, H. The ventilated thermocline. J. Phys. Oceanogr. 13, 292–309 (1983)
Williams, R. G., Spall, M. A. & Marshall, J. C. Does Stommel's mixed layer “demon” work. J. Phys. Oceanogr. 25, 3089–3102 (1995)
Graedel, T. E., Brewer, P. G. & Rowland, F. S. Panel 4. Chemistry of the air-sea interface. Appl. Geochem. 3, 37–48 (1988)
Acknowledgements
We thank A. H. Knap, A. F. Michaels, D. A. Hansell, D. K. Steinberg and C. A. Carlson for their contributions to the BATS program. We also thank the numerous technicians, graduate students, and captains and crew of the RV Weatherbird II, who have contributed to the success of the BATS program since 1988. W. S. Broecker, T. Takahashi, C. D. Keeling and P. G. Brewer are thanked for the use of ΣCO2 data collected in the Sargasso Sea during 1972–86. This work was supported by the National Science Foundation and National Oceanographic and Atmospheric Administration.
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Bates, N., Pequignet, A., Johnson, R. et al. A short-term sink for atmospheric CO2 in subtropical mode water of the North Atlantic Ocean. Nature 420, 489–493 (2002). https://doi.org/10.1038/nature01253
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DOI: https://doi.org/10.1038/nature01253
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