THE RELATIONSHIP BETWEEN SUSPENDED PARTICULATE MATERIAL, PHYTOPLANKTON AND ZOOPLANKTON DURING THE RETREAT OF THE MARGINAL ICE-ZONE IN THE BELLINGSHAUSEN SEA

The distribution, abundance and composition of suspended particulates, phytoplankton and zooplankton biomass were investigated for the margi nal ice zone in the Bellingshausen Sea during the Austral spring of 19 92. Marked changes were observed between the amount and composition of particulates under the sea-ice and those in open waters. Measures of phytoplankton abundance (chlorophyll) ranged from similar to 0.05 mu g 1(-1) under the ice to 3 mu g 1(-1) in the open waters to the north. The high nutrient concentrations and low level of phytoplankton under the ice suggest that this region is typical of over-wintering conditio ns and provides a suitable background comparison to the development of more productive, recently ice-free waters, further north. Nearly all basic measurements of particulate material showed a gradient from sout h to north. However, the biochemistry of particulates (lipid in partic ular), a more sensitive measure of environmental growth conditions, sh owed the area as a whole to be broadly split into two; under ice (ligh t limited) and open water (no light limitation). Total particulate car bon was almost entirely composed of inorganic carbon under the ice; wa ters away from the ice edge also contained significant levels of inorg anic carbon. Hence, C:chlorophyll was estimated from POC or phytoplank ton carbon. There was no evidence of nutrient limitation at any of the stations investigated. Integrated phytoplankton carbon for the upper 100 m ranged from 0.1 gC m(-2) under the ice to 11.5 gC m(-2) in the d iatom dominated bloom in open waters. The mesozooplankton biomass in t he same depth interval increased from 0.02 gC m(-2) under the ice to 0 .21 gC m(-2) In open waters. However, zooplankton biomass in the upper 600 m changed little from under the ice out to open waters north of t he ice edge; although the northernmost station, in the region of highe st chlorophyll, had approximately three times more zooplankton carbon (0.67 gC m(-2)) than the other stations. There is some evidence, howev er, that the northern station may be associated with a frontal feature , and that conditions observed may not be solely related to previous i ce edge processes.