An integrated analysis of geoscience information and benthos data has been used to identify benthic biotopes (seafloor habitats and associated communities) in the nearshore marine environment of the Vestfold Hills, East Antarctica. High-resolution bathymetry and backscatter data were collected over 42km2 to depths of 215 m using a multibeam sonar system. Epibenthic community data and in situ observations of seafloor morphology, substrate composition and bedforms were obtained from towed underwater video. Analysis of the datasets was used to identify statistically distinct benthic assemblages and describe the physical habitat characteristics related to each assemblage, with seven discrete biotopes identified. The biotopes include a range of habitat types including shallow coastal embayments and rocky outcrops which are dominated by dense macroalgae communities, and deep muddy basins which are dominated by mixed invertebrate communities. Transition zones comprising steep slopes provide habitat for sessile invertebrate communities. Areas of flat sandy plains are relatively barren. The relationship between benthic community composition and environmental parameters is complex with many variables (e.g. depth, substrate type, longitude, latitude and slope) contributing to differences in community composition. Depth and substrate type were identified as the main drivers of benthic community composition, however, depth is likely a proxy for other unmeasured depth-dependent parameters such as light availability, frequency of disturbance by ice, currents and/or food availability. Sea ice cover is also an important driver and the benthic community in areas of extended sea ice cover is comprised of sessile invertebrates and devoid of macroalgae. This is the first study that has used an integrated sampling approach based on multibeam sonar and towed underwater video to investigate benthic assemblages across a range of habitats in a nearshore marine environment in East Antarctica. This study demonstrates the efficacy of using multibeam sonar and towed video systems to survey large areas of the seafloor and to collect non-destructive high-resolution data in the sensitive Antarctic marine environment. The multibeam data provide a physical framework for understanding benthic habitats and the distribution of benthic communities. This research provides a baseline for assessing natural variability and human induced change on nearshore marine benthic communities (Australian Antarctic Science Project AAS-2201), contributes to Geoscience Australia's Marine Environmental Baseline Program, and supports Australian Government objectives to manage and protect the Antarctic marine environment.

An integrated analysis of biological and geoscientific data collected from the nearshore marine environment of the Vestfold Hills was used to identify benthic habitats and associated communities and examine relationships between benthic community composition and environmental characteristics. A 48 km2 area was surveyed using a multibeam echosounder system (MBES) to produce high-resolution bathymetry and backscatter intensity maps of the seabed. Epibenthic community data and in situ observations of substrate composition and seafloor bedforms and features were obtained from towed underwater video. A comparison of top-down and bottom-up approaches to defining benthic habitats was used to improve understanding of the applicability of mapping methodologies. On a broad scale, both approaches produced habitat classes distinguished largely by geomorphic features, with substrate and depth identified as the main controls of benthic community composition, however, the relationship between benthic community composition and environmental characteristics is complex with many variables contributing to differences in community composition. The top-down approach was based on geomorphic units defined using abiotic characteristics and the assemblages identified within the geomorphic were very broad did not always show clear distinction between assemblages. Conversely, the bottom-up approach generated additional habitat classes, identified clear defining taxa for each class, greater distinction between the benthic communities, and allowed identification of additional environmental factors (i.e. sea ice cover) that influence benthic community distribution that are not discernible from geomorphic information alone. The habitat types identified and mapped using the bottom-up approach include shallow boulder fields and exposed bedrock which are dominated by dense macroalgae communities, and steep slopes, muddy basins and sandy plains which are dominated by invertebrate communities. The results indicate that a bottom-up approach is preferable for benthic habitat mapping, however, where detailed information is not available, geomorphic information provides a reasonable indication of the distribution of benthic habitats and communities. This study highlights the utility of multibeam sonar for interpretation of sea floor morphology and substrate and the multibeam data provide a physical framework for understanding benthic habitats and the distribution of benthic communities. This research provides the scientific context and spatial framework for managing the Vestfold Hills nearshore marine environment and provides a baseline for assessing environmental change.

Surveying of nearshore areas in the Vestfold Hills using high resolution multibeam swath bathymetry provides both a detailed digital bathymetric model and information on sediment acoustic backscatter. Combined with underwater video transects and sediment sampling, these data can be used to identify and map geomorphic units. Six geomorphic units identified in the survey region include: Rocky outcrops, sediment-floored basins, pediments, steep-sided valleys, scarps and sheltered embayments. In addition to geomorphic units, the data reveal sedimentary structures that provide insights into sediment transport and erosion in the area. Ice keel pits and scours are common while seafloor channels, scour depressions and sand ribbons indicate transport and deposition by wind-driven currents and oceanographic circulation. Gullies and sediment lobes on steep slopes indicate mass movement of sediment. The sheltered embayments preserve a mantle of boulder sand probably deposited by cold-based glaciers. Automated techniques utilizing the bathymetric grid and backscatter to map landforms are useful in defining reproducible boundaries between geomorphic units but cannot easily be adapted to accurately classify the variations in sea floor texture and structure imaged by these data.

Multichannel seismic data collected off Wilkes Land (East Antarctica) reveal four main units that represent distinct phases in the evolution of the Cenozoic depositional environment. A Cretaceous synrift succession is overlain by hemipelagic and distal terrigenous sequences deposited during Phase 1. Sediment ridges and debris-flow deposits mark the transition to Phase 2. Unit 3 records the maximum sediment input from the continent and is characterized by the predominance of turbidite deposits. During Phase 4 the sediment supply from the continental margin was reduced, and draping and filling were the dominant processes on the continental rise. Unit 4 also contains the deposits of sediment wave fields and asymmetric channel-levee systems. These four units are a response to the Cenozoic evolution of the East Antarctic Ice Sheet. During Phase 1, small ice caps were formed in the innermost continental areas. The ice volume increased under temperate glacial regimes during Phases 2 and 3, when large volumes of melt-water production led to high sediment discharge to the continental rise. Change to a polar regime occurred through Phase 4, when a thick prograding wedge developed on the continental shelf and slope and the sediment transport to the rise diminished, producing general starvation conditions.

A late Quaternay, current-lain sediment drift deposit over 30 metres in thickness has been discovered on the continental shelf of East Antarctica in an 850 metre deep glacial trough off George Vth Land. Radiocarbon dating indicates that a period of rapid deposition on the drift occurred in the mid-Holocene, between about 3 000 and 5 000 years before present.

Mawson South Escarpment, Antarctica, geological map 1:250 000

Ice thickness measurements carried out by field parties based on Mawson during 1957-59 consisted of: (:) regional traverses in the form of closed loops extending several hundred kilometres inland from Mawson; (ii) semi-detailed traverses in the vicinity of a line of ice flow stakes about 25 Km from Mawson. The regional traverses showed that, beyond about 175 Km inland, the area surveyed is influenced strongly by the Lambert Glacier - Amery Ice Shelf system situated some 200 Km to the East. Preliminary contour plans of the ice and rock surfaces show fairly close correspondence. A sub-glacial extension of a range of mountains outcropping through the ice 80 Km to the East of the traverses was found. Work along the semi-detailed traverses close to Mawson detected sub-glacial extensions of the outcropping mountain ranges in the area. These extensions may explain the general direction of the coastline near Maws on.

This report outlines the field geophysical work carried out in the vicinity of Wilkes Base (Lat. 660 15' 8, Long. 1100 31' E), Australian Antarctic Territory, during the Australian National Antarctic Research Expedition of 1965-66. The work can be broadly divided into four parts. 1. An autumn traverse where seismic reflection stations were established every 10 miles around a triangle with corners at Cape Folger, the Dome Centre and Cape Poinsett. 2. A mid winter traverse to the inland glaciology station S-2 for a programme of seismic ice velocity studies. 3. A spring traverse where a rectangular grid network of seismic, gravity, and elevation stations were installed in a region between S-2 and 80 miles south of S-2. 4. Two attempts at recording reflections off the Mohorovicic discontinuity shot in the vicinity of Wilkes.

During 1963, the Australian National Antarctic Research Expeditions carried out two over snow traverses in the vicinity of Wilkes Station, Antarctica. The Autumn Traverse reached a point about 100 miles east of Wilkes and the Spring Traverse a point about 300 miles south-east of Wilkes. Surface elevations were measured by barometric methods and ice thicknesses were determined by gravity and seismic techniques. Magnetic measurements were made and borehole temperatures were taken. Experiments were conducted to devise means of improving the quality of the seismic reflection records. The optimum frequency range for the filter settings was found to be 90-215 c/s. A hand-drilled 4-ft shot-hole was adequate in the coastal or low plateau regions within 150 miles of Wilkes. Further inland, a shot hole of at least 30-ft depth was required. The optimum charge size was one pound of explosive.

10-13 July, 1996, University of Tasmania.