Authors: Beaman, R.J.
Publication: P.T. Harris (Editor), Fifth Australian Marine Geoscience Conference, 27-29 June 2001. Consortium for Ocean Geosciences of Australian Universities, Hobart, Australia.
Sediment drift deposits have been recently targeted by international marine geoscience cruises to the East Antarctic continental shelf as they contain important high-resolution records of palaeoenvironmental changes during the Holocene. A summary will be presented of the Jan-Mar 2001 United States RV NATHANIEL B. PALMER cruise, which mapped and cored some 50 stations within the deep continental shelf basins where drift deposits are often found.
The Mertz Drift will be discussed in more detail. This drift was discovered by the Feb-Mar 2000 Italian-Australian WEGA expedition within an 850 metre deep area of the George V Basin. The deposit is over 390 km2 and is composed of biosiliceous ooze up to 30 m thick. The expedition collected 18 piston and gravity cores from 16 sites on the deposit in two cross-drift transects. High-resolution seismic data, seafloor photographs and grab samples were also obtained from the deposit. Sediment cores revealed laminated, olive green, siliceous mud and diatom ooze (SMO) overlying a glacial-marine diamicton. While the lower SMO sediments are laminated, there is a 20 to 50 cm thick sandy drape at the surface overlying the whole drift.
This study found seasonal changes in diatom assemblages within lamination couplets with mean deposition times between 2.6 to 4.3 years. Two currents are believed responsible for the construction of the drift. Upwelled Circumpolar Deep Water transports fine grained sediments southwards towards the inner shelf, and deep, high salinity Shelf Water flows northwesterly along the George V Basin, focusing sinking sediments into a drift deposit. A relative reduction in sea ice during a climatic optimum is believed to be a key factor for reducing bottom currents and the concentration of greater volumes of sediment into the drift.