The North East Water polynya (Greenland Sea) II. Mechanisms of nutrient supply and influence on phytoplankton distribution

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Lara, R. J. , Kattner, G. , Tillmann, U. and Hirche, H. J. (1994): The North East Water polynya (Greenland Sea) II. Mechanisms of nutrient supply and influence on phytoplankton distribution , Polar Biology, 14 , pp. 483-490 .
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The nutrient and phytoplankton distributions in the North East Water polynya (NEW) were determined in June 1991. At Norske Oeer Ice Barrier (the polynya's southern boundary), water was upwelled, but vertical instability precluded the development of phytoplankton blooms. Along the length of the northward coastal current, part of the anticyclonic circulation in this area, the vertical stability increased to the north by the input of melt water and solar heating. This caused a gradual increase in phytoplankton biomass and a decrease in nutrient concentrations until, in the northernmost area, nitrate was depleted at the surface, and sub-surface maxima of chlorophyll a were observed. The band of high chlorophyll a concentrations extending from this area to the south along the eastern margin of the polynya was interpreted as the presence of phytoplankton advected by the local circulation. The phytoplankton communities, consisting mainly of flagellates and diatoms, were typical for the beginning of phytoplankton development in ice-covered areas. They seemed to be partially released from melting ice. Three communities were distinguished, which represented, firstly, the upwelled water and its northern extension, secondly, an area of high phytoplankton biomass in the northwestern part of the polynya, and thirdly, the pack-ice region. The major taxa co-occurred at all stations, with only their relative importance changed. The nutrient concentrations in the NEW were different from those in the adjacent areas. The low nitrate values of about 4 mu M in the upper 70 m, found to be representative for the beginning of the growth season, imposed limitations on the overall phytoplankton production. Therefore, fertilization mechanisms such as upwelling along the Norske Oeer Ice Barrier are important for local nutrient replenishment during the period of active phytoplankton growth. Eventually, silicate and phosphate supplied in higher concentrations by jets of the Arctic outflow may also support phytoplankton production, although these nutrients were not limiting during this study. The high nutrient jets were detected in the upper 100 m of the water column at the eastern boundary of the polynya.

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