Small nanoplankton and bacteria in the Western Ross Sea during sea-ice retreat (spring 1994)

Spatial changes of small nanoplankton (2-10 mu m) were investigated in rela tion to sea-ice conditions, hydrography and receding ice processes in the R oss Sea (Antarctica) during spring 1994. Abundance and biomass of heterotro phic and autotrophic nanoplankton, as well as bacterioplankton, were determ ined along a south-north transect from the open waters polynya towards the pack ice. Autotrophic and heterotrophic nanoplankton biomass ranged from 75 8 to 4570 mgC m(-2) and from 3 to 387 mgC m(-2), respectively. Heterotrophi c nanoplankton accounted, on average, for about 9% of the total (i.e. autot rophic plus heterotrophic) nanoplankton biomass, The size structure of both auto- and heterotrophic nanoplankton in the Ross Sea continental shelf rec eding ice edge was different from that of nanoplankton associated with the shelf break and open Antarctic ice-edge area. Generally, the highest hetero trophic biomass was found in the pack-ice zone on the continental shelf, wh ile the highest heterotrophic contribution to the total nanoplankton biomas s (up to 25%) was encountered at the shelf break where phytoplankton was la rgely dominated by 2- to 3-mu m-size cells.