Enhanced air–sea CO 2 transfer due to water-side convection

Abstract

The exchange of CO 2 between ocean and atmosphere is controlled by the air–sea difference in partial pressure of CO 2 and by the efficiency of the transfer processes, the efficiency can be represented by a resistance of the surface and expressed by transfer velocity, k. Measurements made at the Östergarnsholm field station in the Baltic Sea indicate that the CO 2 transfer velocity is also a function not only of wind speed, but also of the mixed-layer depth of the water and, to a lesser degree, of the stratification of the atmosphere. The transfer velocity is significantly enhanced by a large mixed-layer depth, the enhancement increasing as the surface cooling increases. The impact of mixed-layer depth is expressed by the convective velocity scale of the water (analogous to atmospheric convective scaling). Enhancement due to convection is an important factor affecting the diurnal cycle of air–sea fluxes. Large air–sea temperature differences also occur due to air mass advection. Here water-side convection at wind speeds between 2.5 and 6.5 m s − 1 is investigated. The enhancement due to convection can be added to the traditional transfer velocity.