During the Quaternary, the Mac. Robertson shelf of East Antarctica was deeply eroded by glaciers and currents exposing the underlying basement, resulting in a scalped shelf.

Life in icy waters: A geoscience perspective of life on the Antarctic seafloor

The Rayner Complex of East Antarctica is exposed between 45??80?E in the Enderby Land through Princes Elizabeth Land sector of East Antarctica. It is known to correlate with parts of present day India and to have been deformed and metamorphosed at high grades in the earliest Neoproterozoic (990-900 Ma). The age and origin of the protolith rocks of the Rayner Complex however remains largely unknown, as does the tectonic setting in which these rocks formed. New age data collected from the northern Prince Charles Mountains (eastern Rayner Complex), demonstrate that the pre-orogenic rocks from this region consist of: (1) volcanogenic and terrigenous sediments deposited between 1400 Ma and 1020 Ma in a magmatically active basin characterised by limited input from cratonic sources and, (2) probable syn-sedimentary granitoids dated to 1150 Ma. Our data confirm the continuity of the Rayner Complex into Prydz Bay, a region that preserves a remarkably similar geologic history but which is often differentiated from the Rayner Complex on the basis of a higher grade early Cambrian (~520 Ma) overprint. On the basis of our data we further conclude that the Rayner Complex protoliths likely in formed in a back-arc system that existed along the margin of the pre-Gondwana Indian craton. Anticlockwise P-T paths and high-T, low-P metamorphism associated with the inversion of the Rayner back-arc (990-900 Ma) suggest this event resulted from the accretion of a number of independent microplates, rather than continent-continent collision.

Recently discovered drift deposits on the Antarctic continental shelf provide access to information on the Holocene palaeoceanography of the bottom current regime within deep shelf basins that were previously inaccessible. The George Vth Basin on the East Antarctic margin has been identified by oceanographers as an important source of Antarctic Bottom Water, hence the Holocene history of bottom current activity here may be relevant to variations in bottom water export.

The Antarctic Ice Sheet plays a fundamental role in influencing global climate, ocean circulation patterns and sea levels. Currently, significant research effort is being directed at understanding ice sheet dynamics, ice mass balance, ice sheet changes and the potential impact on, and magnitude of, global climate change. An important boundary condition parameter, critical for accurate modelling of ice sheet dynamics, is geothermal heat flux, the product of natural radiogenic heat generated within the earth and conducted to the earths surface. The total geothermal heat flux consists of a mantle heat component and a crustal component. Ice sheet modelling generally assume an 'average' crustal heat production value with the main variable in geothermal heat flux due to variation of the mantle contribution as a function of crustal thickness. The mantle contribution is typically estimated by global scale seismic tomography studies or other remote methods. While the mantle contribution to the geothermal heat flux is a necessary component, studies of ice sheet dynamics do not generally consider local heterogeneity of heat production within the crust, which can vary significantly from global averages. Heterogeneity of crustal heat production can contribute to significant local variation of geothermal heat flux and may provide crucial information necessary for understanding local ice sheet behaviour and modelling.

The Stillwell Hills region comprises granulite facies gneisses which record evidence for multiple periods of deformation and metamorphism spanning more than 2500 Million years. The predominant orthogneiss package (Stillwell Orthogneiss) represents the margin of an Archaean craton exposed in Enderby Land, some 150 km to the west that was reworked during the late Proterozoic. Younger additions to the crust include Palaeoproterozoic charnockitic gneiss (Scoresby Charnockite) and Meso-Neoproterozoic mafic sills and dykes (Point Noble Gneiss, Kemp Dykes) and felsic pegmatites (Cosgrove Pegmatites). Subordinate supracrustal rocks, including metaquartzite, metapelitic, metapsammitic and calc-silicate gneiss (Dovers Paragneiss, Sperring Paragneiss, Stefansson Paragneiss, Keel Layered Paragneiss, Ives Gneiss) are intercalated and interfolded with the Archaean-Palaeoproterozoic orthogneisses.

Geophysical data were acquired by Australia and Japan from 1994-2002 on the deep-water continental margin offshore from Queen Mary Land, East Antarctica in the general locality of Bruce Rise. This paper presents a regional interpretation of these data and outlines the tectonic history.

Physical and biological characteristics of benthic communities are analysed from underwater video footage collected across the George V Shelf during the 2007/2008 CEAMARC voyage. Benthic habitats are strongly structured by physical processes operating over a range of temporal and spatial scales. Iceberg scouring recurs over timescales of years to centuries along shallower parts of the shelf, creating communities in various stages of maturity and recolonisation. Upwelling of modified circumpolar deep water (MCDW) onto the outer shelf, and cross-shelf flow of high salinity shelf water (HSSW) create spatial contrasts in nutrient and sediment supply, which are largely reflected in the distribution of deposit and filter feeding communities. Long term cycles in the advance and retreat of icesheets (over millennial scales) and subsequent focussing of sediments in troughs such as the Mertz Drift create patches of consolidated and soft sediments, which also provide distinct habitats for colonisation by different biota. These physical processes of iceberg scouring, current regimes and depositional environments, in addition to water depth, are shown to be important factors in the structure of benthic communities across the George V Shelf. The modern shelf communities mapped in this study largely represent colonisation over the past 8-12ka, following retreat of the icesheet and glaciers at the end of the last glaciation (Harris et al., 2001; Ingólfsson et al., 1998). Recolonisation on this shelf may have occurred from two sources: deep-sea environments, and possible shelf refugia on the Mertz and Adélie Banks. However, any open shelf area would have been subject to intense iceberg scouring (Beaman and Harris, 2003). Understanding the timescales over which shelf communities have evolved and the physical factors which shape them, will allow better prediction of the distribution of Antarctic shelf communities and their vulnerability to change. This knowledge can aid better management regimes for the Antarctic margin.

During the late Neogene, the Lambert Glacier-Amery Ice Shelf drainage system flowed across Prydz Bay and showed several changes in flow pattern. In the Early Pliocene, the Lambert Glacier ice stream reached the shelf edge and built a trough mouth fan on the upper continental slope. This was associated with an increase in ice discharge from the Princess Elizabeth Land coast into Prydz Bay. The trough mouth fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. The composition of debris changes at around 1.1 Ma BP from material derived from erosion of the Lambert Graben and Prydz Bay Basin to mostly basement derived material. This probably results from a reduction in the depth of erosion and hence the volume of ice in the system. In the trough mouth fan, debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. Age control in an Ocean Drilling Program hole indicates that most of the trough mouth fan was deposited prior to the Brunhes Matuyama Boundary (780 ka BP). This stratigraphy indicates that extreme ice advances in Prydz Bay were rare after the mid Pleistocene, and that ice discharge from Princess Elizabeth Land became more dominant than the Lambert Glacier ice in shelf grounding episodes, since the mid Pleistocene. Mechanisms that might have produced this change are extreme inner shelf erosion and/or decreasing ice accumulation in the interior of East Antarctica. We interpret this pattern as reflecting the increasing elevation of coastal ice through time and the increasing continentality of the interior of the East Antarctic Ice Sheet. The mid Pleistocene change to 100 ka climatic and sea level cycles may also have affected the critical relationship between ice dynamics and the symmetry or asymmetry of the interglacial/glacial climate cycle duration.

To study the seafloor morpholofy on the George V land shelf, East Antarctica, over 2000 kilometres of high-frequency echo-sounder data were collected between February and March 2000. The acoustic facies are explained in terms of glacial and oceanographic influences on the shelf since the Last Glacial Maximum.