The Davis Coastal Seabed Mapping Survey, Antarctica (GA-4301 / AAS2201 / HI468) was acquired by the Australian Antarctic Division workboat Howard Burton during February-March 2010 as a component of Australian Antarctic Science (AAS) Project 2201 - Natural Variability and Human Induced Change on Antarctic Nearshore Marine Benthic Communities. The survey was undertaken as a collaboration between Geoscience Australia, the Australian Antarctic Division and the Australian Hydrographic Service (Royal Australian Navy). The objectives were to provide multibeam bathymetry and backscatter of the coastal region of the Vestfold Hills around Davis Station, Antarctica, to aid the understanding of sea bed character, benthic habitats, provide a basis for hydrodynamic modeling of water movement around Davis, and to update and extend the navigational charts of the region.

Data from surveys along the East Antarctic margin will be presented to provide insights into the diversity and distribution of benthic communities on the continental shelf and slope, and their relationship to physical processes. Seabed video and still imagery collected from the George V shelf and slope and the sub-ice shelf environment of the Amery Ice Shelf indicate that the benthic communities in these regions are highly diverse, and are strongly associated with the physical environment. Variations in seafloor morphology, depth, sediment type and bottom circulation create distinct seabed habitats, such as muddy basins, rugged slope canyons and scoured sandy shelf banks, which are, in turn, inhabited by discrete seabed communities. The infauna dominated muddy basins contrast sharply with the diverse range of filter-feeding communities that occur in productive canyons and rugged inner shelf banks and channels. In the sub-ice shelf environment, differences in organic supply, linked to the circulation patterns, cause distinct differences in the seabed communities. The strong association between benthic communities and seafloor characteristics allows physical parameters to be used to extend our knowledge of the nature of benthic habitats into areas with little or no biological data. Comprehensive biological surveys of benthic communities in the East Antarctic region are sparse, while physical datasets for bathymetry, morphology and sediment composition are considerably more extensive. Physical data compiled within the proposed network of East Antarctic Marine Protected Areas (MPAs) is used to aid our understanding of the nature of the benthic communities. The diversity of physical environments within the proposed MPAs suggests that they likely support a diverse range of benthic communities.

Within the general trend of post-Eocene cooling, the largest and oldest outlet of the East Antarctic Ice Sheet underwent a change from ice-cliff to ice-stream and/or ice-shelf dynamics, with an associated switch from line-source to fan sedimentation. Available geological data reveal little about the causes of these changes in ice dynamics during the Miocene Epoch, or the subsequent effects on Pliocene-Pleistocene ice-sheet history. Ice-sheet numerical modeling reveals that bed morphology was probably responsible for driving changes in both ice-sheet extent and dynamics in the Lambert-Amery system at Prydz Bay. The modeling shows how the topography and bathymetry of the Lambert graben and Prydz Bay control ice-sheet extent and flow. The changes in bathymetric volume required for shelf-edge glaciation correlate well with the Prydz Channel fan sedimentation history. This suggests a negative feedback between erosion and glaciation, whereby the current graben is overdeepened to such an extent that shelf-edge glaciation is now not possible, even if a Last Glacial Maximum environment recurs. We conclude that the erosional history of the Lambert graben and Prydz Bay in combination with the uplift histories of the surrounding mountains are responsible for the evolution of this section of the East Antarctic Ice Sheet, once the necessary initial climatic conditions for glaciation were achieved at the start of the Oligocene Epoch.

Seismic reflection data show the existence of two major sedimentary basins along the continental margin of Wilkes Land and Terre Adélie, East Antarctica, that contain more than 5 s TWT (> 9 km) of sediments. Four seismic megasequences are identified (MS4 to MS1) that are bounded by: basement, unconformities of interpreted Turonian, Maastrichtian and early Middle Eocene age, and the seafloor. The 4-5 km thick rift and pre-rift sediments are concentrated in a margin-parallel basin (Sabrina Basin). On the basis of seismic correlation with the Australian margin, this basin is interpreted to be of Late Jurassic to mid-Cretaceous age. The post-rift sediments are generally thick along the margin and in the adjacent deep-ocean basin, but are particularly thick in a major depocentre off west Wilkes Land, named here the Budd Coast Basin (BCB). The BCB contains a maximum observed thickness of 5 s TWT (9 km) of post-rift sediments and its location suggests that the sediments were largely derived from a sub-glacial basin currently occupied by the Totten Glacier.

During 2005 Geoscience Australia operated geomagnetic observatories at Kakadu and Alice Springs in the Northern Territory; Charters Towers in Queensland; Learmonth and Gnangara in Western Australia; Canberra in the Australian Capital Territory; Macquarie Island, Tasmania, in the sub-Antarctic; and Casey and Mawson in the Australian Antarctic Territory. Three geomagnetic repeat stations were also occupied in 2005. The Australian Geomagnetism Report 2005 (Volume 53) describes instrumentation and activities; absolute reference magnetometers; data distribution; and presents monthly and annual mean magnetic values, plots of hourly mean magnetic values and K indices at the magnetic observatories and repeat stations operated by Geoscience Australia during calendar year 2005.

Geoscience Australia has recently conducted absolute gravity observations at Davis and Mawson stations in the Australian Antarctic Territory to establish accurate gravity reference points for past and future gravity surveys. These absolute gravity observations are the first such measurements undertaken at any of the Australian Antarctic stations and will not only provide an accurate absolute datum for future gravity work but will also enable gravity surveys that have already been conducted in the Australian Antarctic Territory to be tied to the same datum, thus allowing past and future gravity surveys to be accurately merged and combined.

In 2010, a network of Marine Protected Areas (MPAs) was proposed for the East Antarctic region. This proposal was based on the best available data, which for the benthic regime consisted chiefly of seabed geomorphology and satellite bathymetry data. Case studies from the East Antarctic region indicate that depth and morphology are important factors in delineating marine benthic communities, particularly on the continental shelf. However, parameters such as sediment composition also show a strong association with the distribution and diversity of benthic assemblages. A better assessment of the nature of benthic habitats within the proposed MPA network is now possible with the incorporation of a compilation of sediment properties and higher resolution bathymetry grids across the East Antarctic region (see Figures A and B). Based on these physical properties, and in combination with the seabed morphology, we can now distinguish a range of distinct habitats, such as deep muddy basins, scoured sandy shelf banks, ruggedly eroded slope canyons and muddy deep sea plains. In this presentation, we assess the types of benthic habitats across the East Antarctic region, and then determine how well the proposed MPA network represents the diversity of habitats across this margin. The diversity of physical environments within the proposed MPAs suggests that they likely support a diverse range of benthic communities which are broadly representative of the surrounding region.

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

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.

High-resolution marine sonar swath mapping, covering an area of ca. 33 km2 in the vicinity of the Windmill Islands (67° S, 110° E), Wilkes Land, east Antarctica, permits visualisation and description of the near-shore geomorphology of the seafloor environment in unprecedented detail and provides invaluable insight into the ice-sheet history of the region. Mesoproterozoic metamorphic basement exhibits prominent sets of parallel northwest-trending linear fault sets that probably formed during fragmentation of eastern Gondwana during the Mesozoic. The fault systems appear to control regional coastal physiographic features and have, in places, been preferentially eroded and exploited by subsequent glacial activity. Possibly the earliest formed glacially-derived geomorphological elements are networks of sub-glacial meltwater channels which are preserved on bedrock platforms and ridges. Subtle glacial lineations and streamlined landforms record evidence of the westward expansion of the grounded, Law Dome ice sheet margin, probably during the late Pleistocene Last Glacial Maximum, the direction of which coincides with glacial striae on onshore crystalline bedrock outcrops. The most striking glacial geomorphological features are sets of arcuate ridges confined mostly within glacially excavated `U-shaped valleys, exploiting and developed along bedrock fault sets. These ridge sets are interpreted as `push moraines or grounding zone features, formed during episodic retreat of highly channelised, topographically controlled ice-streams following ice surging, possibly in response to local environmental forcing during the mid-late Holocene. Minor post-glacial marine sedimentation is preserved in several small (1 km2) `isolated marine basins with shallow seaward sills.