Physical and biological oceanographic interaction in the spring bloom at the Bering Sea marginal ice edge zone

Abstract

At the edge of the melting sea ice pack in the Bering Sea in spring, physical, biological, and chemical oceanographic processes combine to generate a short‐lived, intense phytoplankton bloom that is associated with the retreating ice edge. The bloom begins a week or so before the first of May triggered by insolation and by the low‐salinity meltwater stratification in the presence of high nitrate concentrations (∼ > 25 μM). Meltwater (salinity) stratification delineates ice edge blooms from open water blooms where temperature gradients generate the stratification. Five cross‐ice sections of temperature, salinity, σt, chlorophyll, and nitrate are presented as a time series from April 27 to May 5 illustrating the bloom. Evidence of two separate but concurrent blooms in the ice edge zone are presented. In addition, meteorological and oceanographic conditions were observed that should have been conducive to ice edge up welling. While significant ice and water movement occurred, upwelling was not observed. Finally, the Bering Sea ice edge spring bloom is compared with other ice edge systems in both hemispheres, showing that initial Bering Sea nitrate concentrations are among the highest observed but quickly become limiting owing to the rapid build up of phytoplankton populations. This primary production is not coupled to the pelagic Zooplankton because Zooplankton are largely absent on account of the cold temperatures. Observed maximum chlorophyll concentrations in the bloom are several times greater than those observed in other systems.