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 15N 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 pro-duc...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
1994
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.582.5345 http://www.aslo.org/lo/toc/vol_39/issue_7/1630.pdf |
| Summary: | The uptake rates of nitrate, ammonium, and urea were measured with a 15N 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 pro-duction-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 post-bloom 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- I) in open and ice-free parts during the bloom and transition period. Mean growth rate of phytoplankton-nitrogen was 0.5 doubling d-l during the bloom and ranged from 0.3 to 0.4 doubling d-l after the bloom. We hypothesize that primary production in the MIZ is not nutrient limited but is proportional to phy-toplankton standing stocks. Primary production in Arctic waters is char-acterized by a marked seasonality. Primary production increases during the spring as light availability increases and the water column stabilizes. Nutrient levels are maximal in the winter and decrease rapidly during the spring bloom. The concomitant depletion of surface nitrate and reduction of primary production has led to the hypothesis that primary pro-duction becomes nitrogen-limited during the Arctic summer (Harrison and Cota 1991). Zooplankton abundance also varies seasonally and follows the same pattern as primary pro-duction with a 2-3-week lag period (Skjoldal et al. 1987). Grazing by Calanoid copepods consumes 5-20 % of primary production in spring and 65-90 % in summer (Eilertsen et al. 1989). In addition, grazing by microzooplank- |
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