Submerged relict reef systems and modern coral communities discovered around the Balls Pyramid shelf are presented as new evidence of extensive carbonate production at the boundary of reef-forming seas. Balls Pyramid is the southernmost island in a chain of island-reefs in the southwest Pacific Ocean, 24 km south of the southernmost known coral reef in the Pacific Ocean at Lord Howe Island. This paper explores the detailed geomorphic structure of the shelf through the production of a high resolution bathymetric model from multibeam echosounder data and depth estimates from satellite imagery. Key seafloor features identified include a large, mid shelf reef dominating the shelf landscape in 20 - 60 m water depth, mid shelf basins and channels, and shelf margin terrace sequences in 50 - 100 m depth. Sub-bottom profiles, backscatter, drill core and vibro-core data are used to investigate the seafloor composition. Drill cores extracted from the submerged reef surface confirm coral, coralline algae and cemented sands composition, and vibro-core material extracted from unconsolidated areas demonstrate substantial accumulation of carbonates shed from the reef surface. Underwater video imagery reveals abundant modern mesophotic reef communities, including hard corals, colonising the relict reef surface. This paper reveals prolific past reef growth and abundant modern coral growth on what was previously considered to be a planated volcanic shelf outside of reef-forming seas, thus extending understanding of reef evolution at, and beyond, the limits of growth.

Dense hydrocoral-sponge communities have been identified on the upper continental slope of George V Land, East Antarctica and declared Vulnerable Marine Ecosystems. Analysis of physical and biological datasets collected during the 2007/08 CEAMARC survey identified that the richest communities are found in the heads of canyons which receive Antarctic Bottom Water formed on the George V shelf, and the canyons harbouring rich benthos are also those that cut the shelf break. This led to several hypotheses regarding their distribution and three main factors were identified. These hypotheses were tested during a recent marine science voyage in January 2011 to the same region. Initial analysis of the new data supports the hypotheses regarding the physical controls on hydrocoral-sponge community distribution.

This map was created by GA for the purposes of seeking clarifications with AIMS and DFAT for survey work in the Timor Sea. A base map product was modified for the purpose.

This short compilation is a 3D Bathymetric flythrough starting from Exmouth to Fremantle and through the Perth Canyon. Also showing the Houtman, Mentell, Wallaby Plateau, canyons and new volcanoes. This short compilation movie will be incorporated into a PowerPoint presentation to be shown at IUGG 2011. It is in 4:3 format. The 3D flythrough footage was originally created for 08-3476 movie - South West Marine Margin, March 2010.

Abstract: The extent to which fluids may leak from sedimentary basins to the seabed is a critical issue for assessing the potential of a basin for carbon capture and storage. The Petrel Sub-basin, located beneath central and eastern Joseph Bonaparte Gulf in tropical northern Australia, is identified as potentially suitable for the geological storage of CO2 because of its geological characteristics and proximity to offshore gas and petroleum resources. In May 2012, a multidisciplinary marine survey was undertaken to collect data in two targeted areas of the Petrel Sub-basin to facilitate an assessment of CO2 storage potential. Multibeam bathymetry and backscatter mapping (650 km2 over 5,300 line km), combined with acoustic sub-bottom profiling (650 line km) and geomorphological and sediment characterisation of the seabed was undertaken above the CO2 supercritical seal boundary of the sub-basin. Features identified in the high resolution (2 m) bathymetry data include carbonate banks, ridges, pockmark fields and fields of low amplitude hummocks located directly adjacent to banks. Unit and composite pockmarks and clusters of pockmarks are present on plains and adjacent to, and on, carbonate ridges. It is postulated that there are three possible sources for fluids and fluidised gas involved in pockmark formation: deep fluids from the basin, post-Cretaceous intra-formational, layer-bound fluids, and shallow-sourced fluidised gas from the breakdown of organic matter following the Holocene marine transgression of Joseph Bonaparte Gulf.

Models of seabed sediment mobilisation by waves and currents over Australia's continental shelf environment are used to examine whether disturbance regimes exist in the context of the intermediate disturbance hypothesis (IDH). Our study shows that it is feasible to model the frequency and magnitude of seabed disturbance in relation to the dominant energy source (wave-dominated shelf, tide-dominated shelf or tropical cyclone dominated shelf). Areas are mapped where the recurrence interval of disturbance events is comparable to the rate of ecological succession, which meets criteria defined for a disturbance regime. We focus our attention on high-energy, patch-clearing events defined as exceeding the Shields (bed shear stress) parameter value of 0.25. Using known rates of ecological succession for different substrate types (gravel, sand, mud), predictions are made of the spatial distribution of a dimensionless ecological disturbance index (ED), given as: ED = FA (ES/RI), where ES is the ecological succession rate for different substrates, RI is the recurrence interval of disturbance events and FA is the fraction of the frame of reference (surface area) disturbed. Maps for the Australian continental shelf show small patches of ED-seafloor distributed around the continent, on both the inner and outer shelf. The patterns are different for wave-dominated (patches on the outer shelf trending parallel to the coast), tide-dominated (patches crossing the middle-shelf trending normal to the coast) and cyclone-dominated (large oval-shaped patches crossing all depths). Only a small portion of the shelf (perhaps ~10%) is characterised by a disturbance regime as defined here. To our knowledge, this is the first time such an analysis has been attempted for any continental shelf on the earth.

Abstract to appear in conference proceedings as part of GA Record

The legacy of multiple marine transgressions is preserved in a complex morphology of ridges, mounds and reefs on the Carnarvon continental shelf, Western Australia. High-resolution multibeam sonar mapping, underwater photography and sampling across a 280 km2 area seaward of the Ningaloo Coast World Heritage Area shows that these raised features provide hardground habitat for modern coral and sponge communities. Prominent among these features is a 20 m high and 15 km long shore-parallel ridge at 60 m water depth. This ridge preserves the largely unaltered form of a fringing reef and is interpreted as the predecessor to modern Ningaloo Reef. Landward of the drowned reef, the inner shelf is covered by hundreds of mounds (bommies) up to 5 m high and linear ridges up to 1.5 km long and 16 m high. The ridges are uniformly oriented to the north-northeast and several converge at their landward limit. On the basis of their shape and alignment, these ridges are interpreted as relict long-walled parabolic dunes. Their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the post-glacial marine transgression. Some dune ridges abut areas of reef that rise to sea level and are highly irregular in outline but maintain a broad shore-parallel trend. These are tentatively interpreted as Last Interglacial in age. The mid-shelf and outer shelf are mostly sediment covered with relatively low densities of epibenthic biota and have patches of low-profile ridges that may also be relict reef shorelines. An evolutionary model for the Carnarvon shelf is proposed that relates the formation of drowned fringing reefs and aeolian dunes to Late Quaternary eustatic sea level.

The movie describes the marine reconnaisance and seismic surveys undertaken between November 2008 and February 2009 as part of the South-West Margin Project. This is part of the broader part of the Energy Security Program. Video and still images from the marine reconnaisance and seismic surveys. Seismic cross-sections. Bathymetric flythroughs

Prydz Bay and the Mac.Robertson Land Shelf exhibit many of the variations seen on Antarctic continental shelves. The Mac.Robertson Shelf is relatively narrow with rugged inner shelf topography and shalow outer banks swept by the west-flowing Antarctic Coastal Current. U-shaped valleys cut the shelf. it has thin sedimentary cover deposited and eroded by cycles of glacial advance and retreat through the Neogene and Quaternary. Modern sedimention is diatom-rich Siliceosu Muddy OOze in shelf deeps while on the banks, phytodetritus, calcareous bioclasts and terrigenous material are mixed by iceberg ploughing. Prydz Bay is a large embayment fed by the Amery Ice Shelf. it has a broad inner shelf deep and outer bank with depths ranging from 2400 m beneath the ice shelf to 100 m on the outer bank. A clockwise gyre flows through the bay. Fine mud and siliceous ooze drapes the sea floor however banks are scoured by icebergs to depths of 500 m.