The pCO2 variability in the midlatitude North Atlantic Ocean during a full annual cycle

Abstract

The results of 1 year of automated pCO2 measurements in 2002 /2003 onboard the car carrier M/V Falstaff are presented and analyzed with regard to the driving forces that change the seawater pCO2 in the midlatitude North Atlantic Ocean. The pCO2 in surface seawater is controlled by thermodynamics, biology, air-sea gas exchange, and physical mixing. Here we estimate the effects on the annual cycle of pCO2 and relate this property to parameters like SST, nitrate, and chlorophyll. On the basis of the amplitude in seawater pCO 2 for all 4° × 5° grid boxes, this region can be separated into an eastern and western basin. The annual pCO 2 cycle in the eastern basin (10°W-35°W) is less variable, which can be related to the two counteracting effects of temperature and biology; air-sea gas exchange plays a minor role when using climatological MLD. In the western basin (36°W-70°W) the pCO2 amplitude is more variable and strongly follows the thermodynamic forcing, since the biological forcing (as derived from nitrate concentrations) is decreased. Biology and air-sea exchange strongly depend on the MLD and therefore also include physical mixing effects. The pCO2 data of the analyzed region between 34° N and 52°N compare well to the Takahashi et al. [2002] climatology except for regions north of 45°N during the wintertime where the bias is significant. Copyright 2004 by the American Geophysical Union.