Nutrients and phytoplankton biomass distribution and activity at the Barents Sea Polar Front during summer near Hopen and Storbanken

Abstract

In this paper we present data on hydrography, nutrients, phytoplankton biomass distribution and photosynthetic activity from a cruise in early August 2007, covering the waters between the island of Hopen on Spitsbergenbanken and of Storbanken in the Barents Sea. The Polar Front, which separates Atlantic and Arctic waters, was observed along the eastern slope of Spitsbergenbanken at 29.5°E and the western slope of Storbanken around 33°. A surface layer front associated with the meltwater appeared near 26.7°E on Spitsbergenbanken, with strong horizontal temperature and salinity gradients, but relatively weak horizontal density gradients. Phytoplankton biomass was generally low with chlorophyll a (Chl a) concentrations lower than 2mgm−3. No stimulatory front effect was found in this context. The highest concentrations were found as subsurface maximum over Spitsbergenbanken. Nutrients were also low, probably limiting phytoplankton growth. However, enhanced photosynthetic activity was seen near the pycnocline on Storbanken and Spitsbergenbanken, probably an effect of turbulent mixing caused by strong tidal currents, bringing phytoplankton cells in contact with more nutrient rich water, originating from below the pycnocline. Low-light acclimated phytoplankton cells were found at depth in stratified Atlantic Water. About 60% of the nitrate winter reservoir for the upper 100m of the water column had been consumed during the growth season prior to the cruise. This corresponds to a new primary production of 48gCm−2. At the time of the cruise, however, primary production was probably based on regenerated nutrients, conditions that seemed to favour dominance of the coccolithophore Emiliania huxleyi and ultraplankton (<5μm) flagellates.