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

Air-sea exchange of CO(2) can be enhanced under low wind speed and high temperature conditions when a liquid film dominated by molecular diffusion can form at the ocean surface in which hydration-dehydration reactions of CO(2) with water tends to increase the air-sea CO(2) concentration gradient. We estimate this chemical enhancement effect on the air-sea CO(2) fluxes determined either by the product of the exchange coefficient and the air-sea CO(2) partial pressure gradient, or by the (13)C/(12)C 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 decrease 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 velocities, we observe most of the differences in equatorial regions. However, the importance of the chemical enhancement effect in the ocean has yet to be determined. (C) 1999 Elsevier Science Ltd. All rights reserved.