The seasonal and interannual variability of the air-sea CO 2 flux (F ) in the Atlantic sector of the Barents Sea have been investigated. Data for seawater fugacity of CO 2 (f CO 2 sw ) acquired during five cruises in the region were used to identify and validate an empirical procedure to compute f CO 2 sw from phosphate (PO 4 ), seawater temperature (T ), and salinity (S ). This procedure was then applied to time series data of T, S, and PO 4 collected in the Barents Sea Opening during the period 1990-1999, and the resulting f CO 2 sw estimates were combined with data for the atmospheric mole fraction of CO 2 , sea level pressure, and wind speed to evaluate F.
The results show that the Atlantic sector of the Barents Sea is an annual sink of atmospheric CO 2 . The monthly mean uptake increases nearly monotonically from 0.101 mol C m -2 in midwinter to 0.656 mol C m -2 in midfall before it gradually decreases to the winter value. Interannual variability in the monthly mean flux was evaluated for the winter, summer, and fall seasons and was found to be ±0.071 mol C m -2 month -1 . The variability is controlled mainly through combined variation of f CO 2 sw and wind speed. The annual mean uptake of atmospheric CO 2 in the region was estimated to 4.27 ± 0.68 mol C m -2 .