Spring Bloom Development in the Marginal Ice Zone and the Central Barents Sea


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Abstract. The knowledge of the relative contribution of algal groups and the environmental factors that control their abundance in the marginal ice zone of the Barents Sea is rather limited. Therefore, a field investigation to study the hydrography and the phytoplankton composition of the marginal ice zone (MIZ) in the central Barents Sea was carried out along a south-north transect in May 1993. The weakly stratified Atlantic sector of the transect appeared to be in a pre-bloom state and had intermittent intrusions from the meandering Polar Front and the Norwegian Coastal Current, introducing water of a more advanced bloom state. Pico- and nanoplankton flagellates and monads dominated, with a few diatoms and Phaeocystis pouchetii colonies. The average new production rate of 26 g C · m−2 as reflected by NO3 depletion in the euphotic zone, however, indicated that the vernal bloom had been in progress for some time in the Atlantic sector without leaving specific signals in the suspended fraction. The ice-edge and Polar Front area was characterized by a dominance of centric colonial diatom genera Chaetoceros and Thalassiosira with some development of P. pouchetii. In the densely ice-covered and stratified Arctic zone the vernal bloom was at its maximum and dominated by the diatom genera Fragilariopsis and Chaetoceros. Diatoms were limited by silicate concentrations <2 µM in 32% of all samples. New production, as revealed by the C equivalent of nitrate depletion in the upper layer, ranged between 12 g C · m−2 in the north to 45 g C · m−2 in the meandering Polar Front, with an average of about 27 ± 28% g C · m−2. The time development of the vernal bloom in the marginal ice zone and the central Barents Sea in late May 1993, with its complicated zonal structure, was not from south to north, but intermittently from north to south. Later during the year the general development of the vernal bloom was, as expected, from south to north.