Carbon flux in ice–ocean–plankton systems of the Bellingshausen Sea during a period of ice retreat

Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations 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 generated by the interaction between the marginal ice zone and the front. Size-based analyses of the microbial system were derived for ice-covered, recently 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 but 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 losses were far higher than production, although the high sedimentation losses expected were not observed. The carbon flow networks are discussed in relation to the environmental changes and the interaction of the marginal ice zone and the frontal system appears crucial to the phytoplankton. Microzooplankton grazing is implicated as a major controlling factor. The local microbial dynamics are strongly influenced by material which was produced at an earlier time and somewhere else in the Southern Ocean. La plupart des analyses de systèmes microbiens marins dans les zones à couverture saisonnière de glace dans l'Océan Austral reposent sur des données obtenues dans les baies principales des Mers de Ross et de Weddell. Cette étude présente des données collectées en Mer de Bellingshausen à des stations couvrant une gamme de régimes depuis la couverture totale de glace jusqu'à l'eau libre. Une caractéristique majeure du système de production dans cette zone était le retrait rapide de la banquise, ce qui découplait la zone marginale des glaces de la poussée phytoplanctonique, laquelle restait associée à un système frontal. Cette poussée était maintenue, et avait probablement été initiée, dans un environnement inhabituel issu de l'interaction entre la zone marginale des glaces et le front. D