Plankton community structure and dynamics versus physical structure from Terra Nova Bay to Ross Ice Shelf (Antarctica)

During the austral summer 1997/1998, an oceanographic cruise was carried out on a large-scale grid in the Ross Sea. In this contribution, we focused our attention on the coastal area from the Terra Nova Bay (TBN) polynya to the eastern edge of the Ross Ice Shelf (RIS). We analyzed picoplankton, nanoplankton and microplankton fractions, with particular regard toheterotrophy versus autotrophy and the size-based partitioning of living carbon. Plankton dynamics were closely associatedwith hydrological features: (1) diatom blooms were confined to the ice-edge TNB polynya, (2) Phaeocystis dominance was confined to the lower salinity surface waters, diluted by the RIS and the Drygalsky Ice Tongue, (3) heterotrophic communitiesprevailed in the warmer surface waters of the Drygalsky basin, where most of the living carbon was associated with tintinnids(namely Codonellopsis gaussi). Phaeocystis distribution suggested that low salinities may be the main driving force inenhancing their development. In the deepest layers, heterotrophic communities were dominated by bacteria. Along the transect, we did not find evidence of any unique and continuous temporal evolution of the ice melting process, freshening of the water, and warming of the surface layer that trigger summer algal blooms and plankton dynamics. The physical features, which, inturn, mainly depend on the past history of ice retreating, seem to control the development of the planktonic system whichshowed a patchy distribution, shifting from an autotrophic community of the ice-edge area (TNB polynya) to a heterotrophic community of the warmer surface layer in the Drygalsky basin, which was ice-free for a longer period before the sampling.