The abundance and species composition of nannofossil assemblages in sediments from continental shelf to offshore basin, western Tasman Sea

Abstract

Abundance and species composition of recent nannofossil assemblages are described from continental shelf, slope, rise and offshore basin sediments (36 to 37°S Lat.). Shelf and upper slope assemblages contain extremely few nannofossil specimens and species. Numbers of specimens and species diversity increases from slope to basin areas. The overall nannofossil content of the sediment is divided into three groups: all very small species; Gephyrocapsa oceanica; the remaining large species. It is the abundance of the large species which changes most noticeably between shelf, slope, rise and basin areas. Some individual species have specific distribution patterns. Some decrease and others increase in proportion from shelf to basin. Comparing shelf, slope and rise assemblages with basin assemblages indicates that shelf and slope assemblages are not indicative of offshore oceanic hydrological regimes. These differences may be attributed to a variety of hydrological factors which distinguish coastal shelf waters from oceanic waters. Rise assemblages are the shallowest water assemblages which give an indication of offshore oceanic hydrological conditions.