NITROGEN CYCLING IN THE BARENTS SEA - SEASONAL DYNAMICS OF NEW AND REGENERATED PRODUCTION IN THE MARGINAL ICE-ZONE

The uptake rates of nitrate, ammonium, and urea were measured with a N-15 technique during seven cruises in the marginal ice zone (MIZ) in the Barents Sea in 1984-1988. The results from all the cruises were pooled to obtain means for the prebloom, bloom, transition, and postbloom periods. New production-nitrate uptake as percent of total uptake-was high (92-96%) during the prebloom and bloom periods and decreased thereafter. Regenerated production - summed ammonium + urea uptake as percent of total uptake-increased through the bloom cycle and was at its maximum (75-93%) during the postbloom period. New production (as percent of the total) was higher in the ice-filled parts than in the ice-free parts, especially during the postbloom period. Nitrate uptake rates, however, were highest (9-25 nM h(-1)) in open and ice-free parts during the bloom and transition period. Mean growth rate of phytoplankton-nitrogen was 0.5 doubling d(-1) during the bloom and ranged from 0.3 to 0.4 doubling d(-1) after the bloom. We hypothesize that primary production in the MIZ is not nutrient limited but is proportional to phytoplankton standing stocks.