Geological controls on life on the Antarctic sea floor

The Antarctic continental margin has been shaped by geological history and modern processes which in turn influence the benthic communities. Integrating bathymetry, geomorphology, sediment samples and quantitative analysis of sea floorvideo and still images reveals some of these influences. The Antarctic shelf comprises shallow banks separated by inner shelf deeps and cross-shelf valleys. These deeper regions are the primary sites for accumulation of phytodetritus-rich ooze, though many areas are floored by compact subglacial sediments or exposed rock. Bank processes are dominated by iceberg scouring. Quantitative classification of video transects allows multivariant analysis that relates small scale relief and estimates of grain size to biological communities. It shows a complex set of relationships with rocky substrates colonised by bryozoa, sponges and colonial tunicates, while coarse sediment are colonised by sponges and bryozoa. Deep, flat sediment surfaces are colonised by sponges and tunicates and bryozoa, sponges and soft corals colonise the rough sea floor produced by iceberg scours. Muddy sediments are inhabited by infauna, holothurians and shrimps. Most fine sediment is found in the shelf deeps but they also include areas of harder flat sediment probably formed as compact glacial till. The similarity of faunas on iceberg scoured sediment and harder substrates probably reflects compaction of the muddy sea floor sediment by icebergs. Where iceberg scoured sediment is sandy and less cohesive, such as the shallow sea floor around the Vestfold Hills, the scoured surface is flatter and the biota is dominated by infauna such as burrowing bivalves.