Diurnal variability in the oceanic carbon dioxide system and oxygen in the Southern Ocean surface water

During the SWEDARP cruise to the Atlantic sector of the Southern Ocean 1997/1998 six 24-hour stations were occupied in the areas of the Spring Ice Edge (SIE1, SIE2 and SIE3), the Winter Ice Edge (WIE), and the Antarctic Polar Front (APF1 and APF2). Samples were taken at the surface (2 m) every second hour and analyzed for total dissolved inorganic carbon, total alkalinity, pH and dissolved oxygen. By the use of wind speed measurements, calculated fugacity of carbon dioxide, fCO2, and oxygen concentrations in the surface water, sea–air fluxes of carbon dioxide (CO2) and oxygen were calculated. These fluxes and the diurnal change in the chemical properties are discussed in relation to changes in biological activity. The fluctuations in wind speed showed a larger impact on the variability of the calculated fluxes than the fluctuations in surface water fCO2 or oxygen saturation. The calculated fluxes and the variability also showed large differences depending on how the wind speed was used, instantaneously or averaged over 24 hours. The calculated sea–air CO2 fluxes using instantaneous wind speed varied between −0.012 and −0.11 mmol m−2 h−1 in the SIE1, −0.0073 and –0.30 mmol m−2 h−1 in the WIE and –0.043 and –1.65 mmol m−2 h−1 in the APF2. The mean values of sea–air CO2 fluxes were calculated to −0.046±0.044, −0.10±0.094 and −0.52±0.64 mmol m−2 h−1 for the SIE1, WIE and the APF2, respectively. The mean values of sea–air oxygen fluxes were calculated to 0.072±0.073, −0.12±0.54 and 1.4±1.3 mmol m−2 h−1 for the corresponding regions.