Spatial distribution of diatoms in surface sediments from the Indian sector of Southern Ocean

A multidisciplinary scientific expedition to the Southern Ocean (Pilot Expedition to the Southern Ocean PESO) onboard ORV Sagar Kanya during the austral summer of 2004 collected various physical, chemical, biological and geological data/samples. From the sediment cores collected during the expedition, six representative core-top samples were studied along a latitudinal transect from 28 degrees to 56 degrees south to ascertain the modern variation in distribution of siliceous microfossils called diatoms. This is the first Indian attempt to understand the latitudinal variation in the distribution of diatom species in Southern Ocean, its relationship with the changing nutrient availability and/or supply, and its utility in palaeoceanographic reconstruction. In all, 24 diatom species were identified. The diatom population seems to be dominated by seven species namely Fragilariopsis kerguelensis, Fragilariopsis separanda, Thalassionenia nitzschioides, Thalassiothrix spp., Thalassiosira lentiginosa, Eucampia antarctica and Azpeitia tabularis. Of these, F. kerguelensis and T. lentiginosa dominate the diatom community in the Southern Ocean sediments. The spatial distribution of most of the diatoms in surface sediments seems to be controlled by physicochemical parameters like sea surface temperature, salinity, silicate, nitrate and phosphate concentrations.