THE NORTH-EAST WATER POLYNYA (GREENLAND SEA) .2. MECHANISMS OF NUTRIENT SUPPLY AND INFLUENCE ON PHYTOPLANKTON DISTRIBUTION

The nutrient and phytoplankton distributions in the North East Water p olynya (NEW) were determined in June 1991. At Norske Oer Ice Barrier ( the polynya's southern boundary), water was upwelled, but vertical ins tability precluded the development of phytoplankton blooms. Along the length of the northward coastal current, part of the anticyclonic circ ulation in this area, the vertical stability increased to the north by the input of melt water and solar heating. This caused a gradual incr ease in phytoplankton biomass and a decrease in nutrient concentration s until, in the northernmost area, nitrate was depleted at the surface , and sub-surface maxima of chlorophyll a were observed. The band of h igh chlorophyll a concentrations extending from this area to the south along the eastern margin of the polynya was interpreted as the presen ce of phytoplankton advected by the local circulation. The phytoplankt on communities, consisting mainly of flagellates and diatoms, were typ ical for the beginning of phytoplankton development in ice-covered are as. They seemed to be partially released from melting ice. Three commu nities were distinguished, which represented, firstly, the upwelled wa ter and its northern extension, secondly, an area of high phytoplankto n biomass in the northwestern part of the polynya, and thirdly, the pa ck-ice region. The major taxa co-occurred at all stations, with only t heir relative importance changed. The nutrient concentrations in the N EW were different from those in the adjacent areas. The low nitrate va lues of about 4 muM 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 Oer Ice Barrier are important for local nu trient 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 productio n, although these nutrients were not limiting during this study. The h igh-nutrient jets were detected in the upper 100 m of the water column at the eastern boundary of the polynya.