Spatiotemporal variability of inorganic nitrogen stocks and uptake fluxes in the Scotia-Weddell Confluence area during November and December 1988

Abstract

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" latitude. High ammonium concentrations and marked nitrate depletions indicate an enhanced b~ological activity in this part of the ocean. By means of the uptake rates, obtained from I5N 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.