Possible consequences of the chemical enhancement effect for air-sea CO2 flux estimates

Air-sea exchange of CO2 can be enhanced under low wind speed and high tempe rature conditions when a liquid film dominated by molecular diffusion can f orm at the ocean surface in which hydration-dehydration reactions of CO2 wi th water tends to increase the air-sea CO2 concentration gradient. We estim ate this chemical enhancement effect on the air-sea CO2 fluxes determined e ither by the product of the exchange coefficient and the air-sea CO2 partia l pressure gradient, or by the C-13/C-12 isotopic method. We show that the chemical enhancement effect could increase the ocean-atmosphere global net flux retrieved by the direct method by less than 0.1 GtC yr(-1) and can dec rease the one deduced from the 13C/12C isotopic method by 0.2 to 0.3 GtC yr (-1). Since an enhancement effect could exist only for low transfer velocit ies, we observe most of the differences in equatorial regions. However, the importance of the chemical enhancement effect in the ocean has yet to be d etermined. (C) 1999 Elsevier Science Ltd. All rights reserved.