Carbon flux in ice-ocean-plankton systems of the Bellingshausen Sea duringa period of ice retreat

Most analyses of marine microbial systems in the seasonally ice covered are as of the Southern Ocean have been based on data from the major embayment a reas of the Ross and Weddell Seas. In this study data were collected at sta tions covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature of the production system was a rapid retreat of the ice-edge, which uncoupled the marginal ice zone from a phytoplankton bloom which remained associated with a frontal system. This bloom was maintained, and probably initiated, in an unusual environment gen erated by the interaction between the marginal ice zone and the front. Size -based analyses of the microbial system were derived for ice-covered, recen tly ice-covered and open water sites. Estimates of standing stocks and key rate processes were combined to produce a single food web network for each station. The under-ice system was one of low production and low recycling b ut apparently high retention. As the ice retreated the microbial systems to the north began to develop, but these were constrained by grazing pressure . The bloom in the area appeared to be sustained even though estimated loss es were far higher than production, although the high sedimentation losses expected were not observed. The carbon flow networks are discussed in relat ion to the environmental changes and the interaction of the marginal ice zo ne and the frontal system appears crucial to the phytoplankton. Microzoopla nkton grazing is implicated as a major controlling factor. The local microb ial dynamics are strongly influenced by material which was produced at an e arlier time and somewhere else in the Southern Ocean.