Simulated response of the ocean carbon cycle to anthropogenic climate warming

A 1995 report of the Intergovernmental Panel on Climate Change provides a set of illustrative anthropogenic CO2 emission models leading to stabilization of atmospheric CO2 concentrations ranging from 350 to 1,000 p.p.m. (refs 1–4). Ocean carbon-cycle models used in calculating these scenarios assume that oceanic circulation and biology remain unchanged through time. Here we examine the importance of this assumption by using a coupled atmosphere–ocean model of global warming for the period 1765 to 2065. We find a large potential modification to the ocean carbon sink in a vast region of the Southern Ocean where increased rainfall leads to surface freshening and increased stratification. The increased stratification reduces the downward flux of carbon and the loss of heat to the atmosphere, both of which decrease the oceanic uptake of anthropogenic CO2 relative to a constant-climate control scenario. Changes in the formation, transport and cycling of biological material may counteract the reduced uptake, but the response of the biological community to the climate change is difficult to predict on present understanding. Our simulation suggests that such physical and biological changes might already be occurring, and that they could substantially affect the ocean carbon sink over the next few decades.

[1]  John Theodore Houghton,et al.  Climate Change 1992 , 1992 .

[2]  S. Manabe,et al.  Transient response of a coupled model to estimated changes in greenhouse gas and sulfate concentrations , 1997 .

[3]  E. Maier‐Reimer,et al.  Future ocean uptake of CO2: interaction between ocean circulation and biology , 1996 .

[4]  M. McElroy,et al.  Changes in atmospheric CO2: Influence of the marine biota at high latitude , 1984 .

[5]  David C. Lowe,et al.  Variability in the O2/N2 ratio of southern hemisphere air, 1991–1994: Implications for the carbon cycle , 1996 .

[6]  Syukuro Manabe,et al.  Transient responses of a coupled ocean-atmosphere model to gradual changes of atmospheric CO2 , 1991 .

[7]  Kenneth S. Johnson,et al.  Marine Chemistry Discussion Paper What controls dissolved iron concentrations in the world ocean , 1997 .

[8]  J. Sarmiento,et al.  Three‐dimensional simulations of the impact of Southern Ocean nutrient depletion on atmospheric CO2 and ocean chemistry , 1991 .

[9]  P. Tans,et al.  What atmospheric oxygen measurements can tell us about the global carbon cycle , 1993 .

[10]  J. M. Gregory,et al.  Climate response to increasing levels of greenhouse gases and sulphate aerosols , 1995, Nature.

[11]  U. Siegenthaler,et al.  Rapid atmospheric CO2 variations and ocean circulation , 1984, Nature.

[12]  Jorge L. Sarmiento,et al.  Oceanic Carbon Dioxide Uptake in a Model of Century-Scale Global Warming , 1996, Science.

[13]  Raphael Kudela,et al.  A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean , 1996, Nature.

[14]  Syukuro Manabe,et al.  Century-scale effects of increased atmospheric C02 on the ocean–atmosphere system , 1993, Nature.

[15]  Corinne Le Quéré,et al.  AIR-SEA CO2 TRANSFER AND THE CARBON BUDGET OF THE NORTH ATLANTIC , 1995 .

[16]  Ian G. Enting,et al.  Future emissions and concentrations of carbon dioxide: Key ocean / atmosphere / land analyses , 1994 .

[17]  David Archer,et al.  Multiple timescales for neutralization of fossil fuel CO2 , 1997 .

[18]  G. Watts,et al.  Climate Change 1995 , 1998 .

[19]  Corinne Le Quéré,et al.  Limiting future atmospheric carbon dioxide , 1995 .

[20]  J. Sarmiento,et al.  A perturbation simulation of CO2 uptake in an ocean general circulation model , 1992 .

[21]  P. Gent,et al.  Parameterizing eddy-induced tracer transports in ocean circulation models , 1995 .

[22]  J. Toggweiler,et al.  A new model for the role of the oceans in determining atmospheric PCO2 , 1984, Nature.

[23]  David M. Karl,et al.  VERTEX: carbon cycling in the northeast Pacific , 1987 .

[24]  Syukuro Manabe,et al.  Multiple-Century Response of a Coupled Ocean-Atmosphere Model to an Increase of Atmospheric Carbon Dioxide , 1994 .

[25]  R. Wanninkhof.  Relationship between wind speed and gas exchange over the ocean , 1992 .