Annual to interannual variations of fCO(2) in the northwestern Mediterranean Sea: Results from hourly measurements made by CARIOCA buoys, 1995-1997

A time series of fCO(2), SST, and fluorescence data was collected between 1995 and 1997 by a CARIOCA buoy moored at the DyFAMed station (Dynamique des Flux Atmospheriques en Mediterranee) located in the northwestern Mediterranean Sea. On seasonal timescales, the spring phytoplankton bloom decreases the surface water fCO(2) to approximately 290 mu atm, followed by summer heating and a strong increase in fCO(2) to a maximum of approximately 510 mu atm. While the Delta fCO(2) shows strong variations on seasonal timescales, the annual average air-sea disequilibrium is only 2 mu atm. Temperature-normalized fCO(2) shows a continued decrease in dissolved CO2 throughout the summer and fall at a rate of approximately 0.6 mu atm d(-1). The calculated annual air-sea CO2 transfer rate is -0.10 to -0.15 moles CO2 m(-2) y(-1), with these low values reflecting the relatively weak wind speed regime and small annual air-sea fCO(2) disequilibrium. Extrapolating this rate over the whole Mediterranean Sea would lead to a flux of approximately -3 x 10(12) to -4.5 x 10(12) grams C y(-1), in good agreement with other estimates. An analysis of the effects of sampling frequency on annual air-sea CO2 flux estimates showed that monthly sampling is adequate to resolve the annual CO2 flux to within approximately +/- 10 - 18% at this site. Annual Aux estimates made using temperature-derived fCO(2) based on the measured fCO(2)-SST correlations are in agreement with measurement-based calculations to within +/-7-10% (depending on the gas transfer parameterization used), and suggest that annual CO2 flu estimates may be reasonably well predicted in this region from satellite or model-derived SST and wind speed information.