The fugacity of CO2 (fCO(2)) and the content of chlorophyll alpha in surface-water were determined during consecutive sections between 47 degrees and 60 degrees S along 6 degrees W in austral spring, October-November 1992. In the Polar Frontal region, the fCO(2) of surface-water decreased from slightly below the atmospheric value to 50 mu atm below it. This was accompanied by the development of diatom blooms. Seasonal warming of 1.2 degrees C and air-sea exchange partly compensated the decrease of fCO(2) by biological activity. Meanders of the Polar Frontal jet and a mesoscale eddy were reflected in spatial variability of fCO(2) and chlorophyll a. Systematic observations indicated relationships between fCO(2) and chlorophyll a, albeit changing with time. The combination of biological CO2-uptake with formation of Antarctic Intermediate Water (AAIW) makes the Polar Front a site of combined biological/physical CO2-drawdown from the atmosphere. In the southern part of the Antarctic Circumpolar Current (sACC) and the Southern Frontal region, fCO(2) increased 7-8 mu atm due to surface-water warming of 0.5 degrees C. A sharp rise of surface water fCO(2) of 13 mu atm occurred south of the southern Frontal jet. As the ice-cover disappeared, the Boundary between the ACC and the Weddell Gyre released significant amounts of CO2. The Weddell Gyre would become a strong CO2-source after the imminent retreat of the ice. Clearly mechanisms behind changes of fCO(2) in surface waters differ for the hydrographic regions. Interstitial brines of sea-ice had fCO(2) as low as 100 mu atm and had been depleted in nutrients. The summation of significant sources and sinks in the different regions indicates an overall minor oceanic CO2-sink of 0.3 mmol m(-2) day(-1) throughout the cruise, on the basis of the Wanninkhof relationship at in situ wind speed without skin effect. Uptake of CO2 increased to 1.0 mmol m(-2) day(-1), when a uniform cold skin temperature difference of 0.2 degrees C was assumed. The skin temperature difference derived from the physical model by Soloviev and Schlussel (1994a,b) had an average value of 0.2 degrees C, leading to an uptake of CO2 of 1.2 mmol m(-2) day(-1). The measured skin temperature difference exceeded the calculated value. These assessments underline the uncertainty in the estimated air-sea exchange of CO2 due to the thermal shin effect, the chosen parametrization of the gas transfer velocity, and the selected length of the wind speed interval. Limited understanding of the mechanistics of gas exchange, as well as large seasonal and spatial variability of the air-sea flux, still preclude a reliable estimate of the basin-wide annual flux for the Southern Ocean. (C) 1997 Elsevier Science Ltd.
