On the role of heat fluxes in the uptake of anthropogenic carbon in the North Atlantic

• Published in: Global Biogeochemical Cycles
• Main Authors: Völker, Christoph, Wallace, D. W. R., Wolf-Gladrow, Dieter
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2002
• Subjects: North Atlantic
• Online Access: https://epic.awi.de/id/eprint/5247/; https://doi.org/10.1029/2002GB001897; https://hdl.handle.net/10013/epic.15815

The influence of the overturning circulation on the anthropogenic carbonsink in the North Atlantic is investigated with a simple box model.The net air-sea flux of anthropogenic carbon inthe North Atlantic is the result of two opposing fluxes:The first is the uptake caused by the disequilibriumbetween the rapidly rising atmospheric pCO2and the dissolved carbon content in the ocean, depending mainly onthe water exchange rate between mixed layer and interior North Atlantic ocean.Superimposed is a second flux, related to the northwardtransport of heat within the Atlantic basin, that is directed out of theocean, contrary to conventional wisdom. It is caused by a latitudinalgradient in the ratio of seawater alkalinity to totaldissolved inorganic carbon that in turnis related to the cooling and freshening of surface water on its waynorth. This flux depends strongly on the verticalstructure of the upper branch of the overturningcirculation and on the distribution of under- andsuper-saturation of CO2 in Atlantic surface waters.A data-based estimate of anthropogenic carboninventory in the North Atlantic is consistent with a dominance of thedisequilibrium flux over the heat-flux-related outgassing at thepresent time, but, in our model, does not place astrong constraint on the net anthropogenic air-sea flux.Stabilization of the atmospheric pCO2 on a higher levelwill change the relative role of the two opposing fluxes, making the NorthAtlantic a source of anthropogenic carbon to the atmosphere.We discuss implications for the interpretation ofnumerical carbon cycle models.