Primary productivity and new production in the Northeast Water (Greenland) Polynya during summer 1992

Abstract

The primary productivity and rates of new production were assessed in the Northeast Water Polynya during July–August 1992 by using 14C and 15N tracer techniques. The average rate of primary production for the entire region, including an approximate correction for the effects of ice cover, was 0.21 g C m−2 d−1, with the maximum observed rate being slightly over 1.1 g C m−2 d−1. Rates of new production (uncorrected for effects of ice cover) averaged 3.08 mmol N m−2 d−1. Surface f ratios (the ratio between nitrate uptake and the total inorganic nitrate uptake) averaged 0.63, and depth‐integrated f ratios equaled 0.69. It appeared that the water column in general was bilayered, in that f ratios were reduced near the surface in low (less than 2 μM) nitrate waters and increased deeper in the euphotic zone. Ammonium concentrations and uptake were consistently low throughout the region. Growth rates were modest, with surface growth rates averaging 0.33 per day. A simple relationship among the attenuation of solar radiation by sea ice (and its associated snow cover and microbial community), the percentage of open water, ice thickness, water column attenuation, and phytoplankton photosynthesis is described. The relationship is nonlinear, but, in general, nutrient‐replete water column photosynthesis are largely a function of the percentage of open water rather than ice thickness. Both irradiance and nutrient fields exert strong influences on phytoplankton productivity and ultimately result in a mosaic of biomass within the polynya.