Estimates of anthropogenic carbon in the Indian Ocean with allowance for mixing and time‐varying air‐sea CO2 disequilibrium

[1] We apply to the Indian Ocean a novel technique to estimate the distribution, total mass, and net air-sea flux of anthropogenic carbon. Chlorofluorocarbon data are used to constrain distributions of transit times from the surface to the interior that are constructed to accommodate a range of mixing scenarios, from no mixing (pure bulk advection) to strong mixing. The transit time distributions are then used to propagate to the interior the surface water history of anthropogenic carbon estimated in a way that includes temporal variation in CO2 air-sea disequilibrium. By allowing for mixing in transport and for variable air-sea disequilibrium, we remove two sources of positive bias common in other studies. We estimate that the anthropogenic carbon mass in the Indian Ocean was 14.3–20.5 Gt in 2000, and the net air-sea flux was 0.26–0.36 Gt/yr. The upper bound of this range, the no-mixing limit, generally coincides with previous studies, while the lower bound, the strong-mixing limit, is significantly below previous studies.

[1]  C. Goyet,et al.  New determination of carbonic acid dissociation constants in seawater as a function of temperature and salinity , 1989 .

[2]  Wolfgang Roether,et al.  Temporal evolution of CFC 11 and CFC 12 concentrations in the ocean interior , 1996 .

[3]  W. Owens,et al.  The Importance of Lateral Diffusion for the Ventilation of the Lower Thermocline in the Subtropical North Atlantic , 2000 .

[4]  M. England,et al.  An off‐line 3D model of anthropogenic CO2 uptake by the oceans , 2001 .

[5]  P. Brewer.  Direct observation of the oceanic CO2 increase , 1978 .

[6]  V. Ittekkot,et al.  Determination of anthropogenic CO2 in the North Atlantic Ocean using water mass ages and CO2 equilibrium chemistry , 2001 .

[7]  J. Sarmiento,et al.  Anthropogenic CO2 Uptake by the Ocean Based on the Global Chlorofluorocarbon Data Set , 2003, Science.

[8]  Thomas W. N. Haine,et al.  A Generalized Transport Theory: Water-Mass Composition and Age , 2002 .

[9]  T. Haine,et al.  Inferring the concentration of anthropogenic carbon in the ocean from tracers , 2002 .

[10]  Samar Khatiwala,et al.  Age Tracers in an Ocean GCM , 2001 .

[11]  W. Liu,et al.  CO2 exchange coefficients from remotely sensed wind speed measurements: SSM/I versus QuikSCAT in 2000 , 2002 .

[12]  R. Fine,et al.  Circulation of tritium in the Pacific Ocean , 1981 .

[13]  R. Matear,et al.  Can CFCs be used to determine anthropogenic CO2? , 2003 .

[14]  Timothy M. Hall,et al.  Transit-Time and Tracer-Age Distributions in Geophysical Flows , 2000 .

[15]  Thomas W. N. Haine,et al.  Relationships among tracer ages , 2003 .

[16]  R. Healy,et al.  Spatial variation of total CO2 and total alkalinity in the northern Indian Ocean : A novel approach for the quantification of anthropogenic CO2 in seawater , 1999 .

[17]  F. Millero,et al.  Gradual increase of oceanic CO2 , 1979, Nature.

[18]  J. Karstensen,et al.  Water subducted into the Indian Ocean subtropical gyre , 2002 .

[19]  C. Sweeney,et al.  Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects , 2002 .

[20]  W. Jenkins.  The use of anthropogenic tritium and helium-3 to study subtropical gyre ventilation and circulation , 1988, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[21]  R. Weiss,et al.  Solubilities of chlorofluorocarbons 11 and 12 in water and seawater , 1985 .

[22]  R. Feely,et al.  Comparison of recent Indian Ocean anthropogenic CO2 estimates with a historical approach , 2001 .

[23]  Jorge L. Sarmiento,et al.  Tracer dating and ocean ventilation , 1990 .

[24]  Syukuro Manabe,et al.  Simulated response of the ocean carbon cycle to anthropogenic climate warming , 1998, Nature.

[25]  E. Maier‐Reimer,et al.  Estimates of anthropogenic carbon uptake from four three‐dimensional global ocean models , 2001 .

[26]  A. Basu,et al.  The Inverse Gaussian Distribution , 1993 .

[27]  R. Feely,et al.  Comparison of methods to determine the anthropogenic CO2 invasion into the Atlantic Ocean , 1999 .

[28]  R. Weiss,et al.  Reconstructed histories of the annual mean atmospheric mole fractions for the halocarbons CFC‐11 CFC‐12, CFC‐113, and carbon tetrachloride , 2000 .

[29]  A. Bower,et al.  Character and dynamics of the Red Sea and Persian Gulf outflows , 2000 .

[30]  R. Sonnerup.  On the relations among CFC derived water mass ages , 2001 .

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

[32]  N. Gruber,et al.  Comparison of two approaches to quantify anthropogenic CO2 in the ocean: Results from the northern Indian Ocean , 2001 .

[33]  T. Stocker,et al.  An improved method for detecting anthropogenic CO2 in the oceans , 1996 .

[34]  K. Johnson,et al.  Anthropogenic CO2 inventory of the Indian Ocean , 1999 .

[35]  M. Tomczak,et al.  Thermocline circulation and ventilation in the Indian Ocean derived from water mass analysis , 1993 .