LATE AUSTRAL SPRING DIATOM DISTRIBUTION BETWEEN NEW-ZEALAND AND THE ROSS ICE SHELF, ANTARCTICA - HYDROGRAPHIC AND SEDIMENT CORRELATIONS

Six diatom assemblages were identified in 10 surface water samples taken along a north-south track in December 1976, between New Zealand and the Ross Ice Shelf. These were further divided into two groups, whose boundary is approximately marked by: 1) the 0.degree. C sea surface isotherm; 2) a surface salinity minimum; 3) the northward limit of high-silicate surface water; and 4) the presence of sea-ice to the south. The northern group (two assemblages) is characterized by open ocean forms while the southern group (four assemblages) is characterized by ice-edge and near-ice forms. Diatom abundance along this track appears to be dictated by temperature and nutrients and the dampening effects of sea-ice on surface water productivity. We could not, however, rule out other factors such as differing nutrient concentrations and proportions and water column stability. A number of surface water assemblages could also be observed in the underlying surface sediments after allowing for dissolution in the water column and the homogenizing effects of deep and bottom water currents.