| Summary: | The location of the main Southern Ocean frontal systems, identified from surface water data for salinity and temperature during INDIGO 3, determines the surface water values for nitrate, silica and barium. For nitrate the strongest gradient coincides with the Subtropical Convergence (STC; 42°S). with zero concentration north of this front and concentrations from 17 to 27 µmol/l south of it. North of the STC silica never is completely exhausted, while dissolved barium concentrations decrease to 40 nmol/l, the lowest values observed. Along the watercolumn within the Circumpolar Current the following watermasses are identified (from surface to bottom) : Antarctic Surface Water, Winter Water, Circumpolar Deep Water, Weddell Sea Deep Water and Antarctic Bottom Water. Here, typical profiles for dissolved barium show surface values of 77 nmol/l and bottom values of 100 nmol/l. Along Antarctica some stations show a decrease in dissolved barium and silica in bottom waters. This indicates local bottom water formation, confirmed by freon-11 data for two stations in Wild Canyon (west of Amery Basin). The maxima of particulate barium in the euphotic layer (-35m) and the oxygen minimum layer (-200m) suggest that both, active (the living phytoplankton cell) and passive (the desintegration of organic detritus microenvironments) processes control the production of barite.
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