Surface layer balance of the southern Antarctic Circumpolar Current (primemeridian) used to derive carbon and silicate consumptions and annual air-sea exchange for CO2 and oxygen

A simple model, using concentrations of nitrate and phosphate in austral wi nter 1992, reveals that the Antarctic Surface Water (AASW) of the southernm ost Antarctic Circumpolar Current (ACC) between the Southern ACC Front and the Weddell Front is made up of similar to 90% Upper Circumpolar Deep Water (UCDW) and 10% northward flowing AASW from the Weddell Gyre. With a typica l timescale of similar to 1 year the upwelling velocity tvas calculated to be as high as 60-100 m yr(-1). Knowing the composition of the surface water with respect to its sources, changes due to several processes in the surfa ce layer were deduced for carbon dioxide, oxygen, and silicate. As the time scale of changes in the surface layer of the southern ACC is similar to 1 y ear, this allows us to calculate changes on an annual basis without interfe rence of short-term variations. Balancing the contributions by upwelling, b iological activity, and air-sea exchange to the concentrations in the surfa ce layer, the area was found to be a large sink for atmospheric oxygen of 6 .0 mol m(-2) yr(-1) (53 mu mol kg(-1)) and a small sink for atmospheric car bon dioxide of 1.0 mol m(-2) yr(-1) (9 mu mol kg(-1)), The most important c ause For the oxygen sink is the upwelling of oxygen-poor UCDW, which surpas ses the oxygen-elevating effect of primary productivity. This large oxygen sink, in between areas to the north and south which are only a small sink o r even a source, conforms with the latitudinal distribution of atmospheric oxygen, The small CO2 sink is largely brought about by biological activity. The annual carbon utilization amounts to 76 +/- 22 g C m(-2) yr, which is relatively high for an open ocean region in the Antarctic. However, it supp orts recent estimates of primary production of the Antarctic Ocean that are higher than early published values. The annual silicate consumption was ca lculated to be 126 +/- 19 g Si m yr(-1), This is considerably higher than t he Southern Ocean mean in current estimates, Although the southernmost ACC may be atypical for the Southern Ocean, the current estimate for Southern O cean silica production may well be an underestimation. The silicate to carb on utilization ratio derived here is 0.53 which aligns with investigations on Antarctic phytoplankton and thus underscores the consistency of our resu lts.