SPATIOTEMPORAL VARIABILITY OF INORGANIC NITROGEN STOCKS AND UPTAKE FLUXES IN THE SCOTIA-WEDDELL CONFLUENCE AREA DURING NOVEMBER AND DECEMBER 1988

Distributions of nitrate and ammonium and corresponding uptake fluxes were investigated in the Scotia-Weddell Confluence area during EPOS LEG 2 (November and December 1988) on board RV 'Polarstern'. In this area a central low-salinity and low-nitrate compartment extends southward from the Scotia Front over 1 to 1.5-degrees-latitude. High ammonium concentrations and marked nitrate depletions indicate an enhanced biological activity in this part of the ocean. By means of the uptake rates, obtained from N-15 incubations, and of nitrate depletion data it is proved that this marginal ice zone ecosystem shifts from predominantly new production based (highest f-ratio 0.83) to regenerated production based (lowest f-ratio 0.30) after some 3 wk. This transition corresponds with the change from a higher diatom presence to a higher flagellate presence in the phytoplankton community. Moreover, it is in agreement with the described sudden termination of export fluxes in the Weddell Sea.