Abstract
Sea surface fugacity of carbon dioxide (fCO 2 ssw) was measured across the Weddell gyre and the eastern sector in the Atlantic Southern Ocean in autumn. During the occupation between February and April 2019, the region of the study transect was a potential ocean CO 2 sink. A net CO 2 flux (FCO 2 ) of −6.2 (± 8; sink) mmol m –2 d –1 was estimated for the entire study region, with the largest average CO 2 sink of −10.0 (± 8) mmol m –2 d –1 in the partly ice-covered Astrid Ridge (AR) region near the coast at 68°S and −6.1 (± 8) mmol m –2 d –1 was observed in the Maud Rise (MR) region. A CO 2 sink was also observed south of 66°S in the Weddell Sea (WS). To assess the main drivers describing the variability of fCO 2 ssw, a correlation model using fCO 2 and oxygen saturation was considered. Spatial distributions of the fCO 2 saturation/O 2 saturation correlations, described relative to the surface water properties of the controlling variables (chlorophyll a, apparent oxygen utilization (AOU), sea surface temperature, and sea surface salinity) further constrained the interplay of the processes driving the fCO 2 ssw distributions. Photosynthetic CO 2 drawdown significantly offsets the influence of the upwelling of CO 2 -rich waters in the central Weddell gyre and enhanced the CO 2 sink in the region. FCO 2 of −6.9 mmol m –2 d –1 estimated for the Weddell gyre in this study was different from FCO 2 of −2.5 mmol m –2 d –1 in autumn estimated in a previous study. Due to low CO 2 data coverage during autumn, limited sea-air CO 2 flux estimates from direct sea-surface CO 2 observations particularly for the Weddell gyre region are available with which to compare the values estimated in this study. This highlights the importance of increasing seasonal CO 2 observations especially during autumn/winter to improving the seasonal coverage of flux estimates in the seasonal sea ice-covered regions of the Southern Ocean.