Nitrogen uptake and new production in the Greenland Sea: The spring Phaeocystis bloom

Abstract

Nitrogen (nitrate and ammonium) uptake was measured in the Greenland Sea during April–May 1989 as part of the Coordinated Eastern Arctic Experiment (CEAREX). The region was dominated by a massive bloom of Phaeocystis pouchetii, and particulate nitrogen concentrations reached 450 mmol m−2 within the bloom. Particulate carbon:nitrogen ratios were similar to other polar assemblages, suggesting that the particulate matter composition was not dominated by carbon‐rich extracellular material. Vertically integrated f ratios ranged from 0.09 to 0.90 and generally decreased with time, as did nitrate concentrations. Nitrate uptake rates showed no temporal trend, but ammonium uptake rates were low initially and increased greatly by the end of the study. New production rates were very high, with carbon‐based productivities calculated from nitrate uptake rates and observed C:N ratios up to 4.9 g C m−2 d−1. Based on a simple mass balance of organic matter, much (∼60%) of the biogenic material produced in the Phaeocystis bloom apparently was removed from the surface layer. It is hypothesized that the formation of aggregates led to increased fluxes of particulate organic matter from the surface layer. As a result, Phaeocystis blooms may play important roles in the vertical transport of carbon and nitrogen in the Greenland Sea.