A numerical model of mesoscale physical‐biological interactions in the Fram Strait marginal ice zone

A numerical model of marginal ice zones is presented which includes ice-atmosphere-ocean interactions and couples biological processes to the physical dynamics of the ice edge. We have used initial conditions from the Fram Strait in spring when stratification is increasing, nutrient concentrations are high, and solar radiation is increasing, conditions which are found prior to an ice edge phytoplankton bloom. We present three sets of experiments: (1) a standard case (and variations resulting from different initial conditions) with oceanic and ice melt stratification, but no winds or eddies, (2) one with wind forcing and ice cover but no eddies, and (3) cases with cyclonic and anticyclonic eddies under ice cover. In general, stratification within the upper layers accelerates the growth and accumulation of phytoplankton. When the stratification is due to ice melt only, the bloom is horizontally constrained between the ice and the ice edge frontal structure. Maximum primary productivity occurs 7 to 10 days after the introduction of stratification, and chlorophyll reaches a maximum approximately 3 days later. The bloom's biomass is eventually limited by nutrients. Wind-driven ice edge upwelling alone was ineffective in stimulating phytoplankton growth. However, any wind-induced horizontal movement of ice either uncovers nutrient-rich water or advects nutrients into open water, which stimulates phytoplankton growth. When a cyclonic eddy rotates under the ice, a surface divergence results, causing the ice to open in the center, while upwelling at the eddy core injects nutrients into the euphotic zone. Anticyclonic eddies induce downwelling at the eddy's core and upwelling and surface divergence at the outer edges. With the increased irradiance and high nutrient concentrations, phytoplankton biomass within the eddy increases rapidly.

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