Mechanisms Controlling the Air-Sea Flux of CO 2 in the North Atlantic

Abstract

The air-sea flux of carbon is controlled by the disequilibrium in partial pressure of carbon dioxide between the atmosphere and surface ocean. This disequilibrium is a consequence of the interactions of physical, chemical and biological processes in the ocean and, today, includes a response to the anthropogenic increase of atmospheric pCO 2. Fig. 1 illustrates the annual mean airsea flux of carbon, F, estimated from a knowledge of the atmospheric partial pressure, pCO 2 at and compilation of surface pCO 2 observations by Takahashi et al. (1999). The air-sea flux of carbon is determined by (1) F=−KgK0(pCO2−pCOat2 where K 0 is the solubility of CO 2 at local temperature and salinity. K g is the air-sea gas transfer coefficient, which is dependent on local environmental conditions and is usually parameterized as a function of wind speed, sea-surface temperature and sea-surface salinity (Wanninkhof, 1992). The major global scale features in Fig. 1 are the outgassing of CO 2 from the tropical oceans, and the influx at mid and high latitudes. In this chapter we focus on understanding what sets the basin wide, and regional patterns of air-sea carbon flux in the North Atlantic basin. While we focus on the North Atlantic, some of the concepts and discussions are also relevent to other regions of the ocean.