From 1 - 10 / 215
  • This dataset contains sediment and geochemistry information for the Oceanic Shoals Commonwealth Marine Reserve (CMR) in the Timor Sea collected by Geoscience Australia during September and October 2012 on RV Solander (survey GA0339/SOL5650). Further information on the survey is available in the post-survey report published as Geoscience Australia Record 2013/38: Nichol, S.L., Howard, F.J.F., Kool, J., Stowar, M., Bouchet, P., Radke, L., Siwabessy, J., Przeslawski, R., Picard, K., Alvarez de Glasby, B., Colquhoun, J., Letessier, T. & Heyward, A. 2013. Oceanic Shoals Commonwealth Marine Reserve (Timor Sea) Biodiversity Survey: GA0339/SOL5650 - Post Survey Report. Record 2013/38. Geoscience Australia: Canberra. (GEOCAT #76658).

  • The Leeuwin Current has significant ecological impact on the coastal and marine ecosystem of south-western Australia. This study investigated the spatial and temporal dynamics of the Leeuwin Current using monthly MODIS SST dataset between July 2002 and December 2012. Topographic Position Index layers were derived from the SST data for the mapping of the spatial structure of the Leeuwin Current. The semi-automatic classification process involves segmentation, 'seeds' growing and manual editing. The mapping results enabled us to quantitatively examine the current's spatial and temporal dynamics in structure, strength, cross-shelf movement and chlorophyll a characteristic. It was found that the Leeuwin Current exhibits complex spatial structure, with a number of meanders, offshoots and eddies developed from the current core along its flowing path. The Leeuwin Current has a clear seasonal cycle. During austral winter, the current locates closer to the coast (near shelf break), becomes stronger in strength and has higher chlorophyll a concentrations. While, during austral summer, the current moves offshore, reduces its strength and chlorophyll a concentrations. The Leeuwin Current also has notable inter-annual variation due to ENSO events. In El Niño years the current is likely to reduce strength, move further inshore and increase its chlorophyll a concentrations. The opposite occurs during the La Niña years. In addition, this study also demonstrated that the Leeuwin Current has a significantly positive influence over the regional nutrient characteristics during the winter and autumn seasons. Apart from surface cooling and advection, the Leeuwin Current's sizable cross-shelf movement may be another contributing factor to the seasonal and inter-annual variations of its chlorophyll a concentrations.

  • A biophysical dispersal model was used to simulate hydrodynamic connectivity among canyons located within Australia's South-west marine region. The results show that exchange among canyons in this area is greatly influenced by the Leeuwin current, transporting larvae in a unidirectional manner around Cape Leeuwin, and continuing eastwards along the Great Australian Bight. Larvae within canyons tend to remain within them, however if they are transported above the canyon walls, they then have the opportunity to be transported significant distances (thousands of kilometres). Analysis of the variability in connectivity patterns reveals concentrated flow near the shelf break, with increasing levels of variability leading offshore from the canyons. While the average potential flow distance and duration between canyons were approximately 550 kilometres and 33 days respectively, the average realized flow distance and duration were approximately 30 kilometres and 6 days respectively. This study provides the first consideration of connectivity among submarine canyons and will help improve management of these features by providing a better understanding of larval movement, transboundary exchange and the potential spread of invasive species.

  • Bathymetric flythrough of the Southeast Margin of Australia for a Powerpoint presentation on the Marine Geoscience capabilities of the RV Investigator. The presentation will be given at the Welcome to Port Ceremony for the ship.

  • Submarine canyons are highly energetic and dynamic environment. Owing to their abrupt and complex topographies that are contrast to the adjacent shelf and slope, they can generate intense mixing, both horizontally through internal tides and waves and vertically through upwelling and downwelling. Complex hydrodynamic processes and increased food supply in sediment and water column result in elevated primary and secondary production which would favour the development of a highly productive and temporally dynamic food web over the canyons. Consequently, many submarine canyons, especially those incise into continental shelf, are considered as biodiversity hotspots. To better understand the ecosystem functions and ecological processes of marine environment, identification and classification of submarine canyons are needed. This study developed a national-scale submarine canyon classification system for Australian ocean based on canyon's physical characteristics. A hierarchical classification scheme was proposed. At the top level, the submarine canyons were classified into shelf-incising canyons and confined-to-slope canyons. At the lower levels, the canyons were classified on their morphometry, shape and location characteristics separately. Accurate identification of submarine canyons was the critical first step for the success of the proposed canyon classification system. A national bathymetry data at a spatial resolution of 250 metres and a completed set of multibeam bathymetry data at a spatial resolution of 50 metres from all previous multibeam surveys, both published by Geoscience Australia, were used. Hill-shaded layers were generated from which most submarine canyons could be easily identified. The extents of individual canyons, from wall to wall, were manually digitised as a GIS polygon layer. The initial number of canyons was then filtered using the following criteria: - Depth of the canyon head is less than 4000 m, - Depth range between the canyon's head and foot is greater than 600 m, and - Incision of the canyon head is greater than 100 m. At the lower levels, the following metrics were calculated as the inputs to the canyon classifications: - Morphometry metrics: incision depth of the canyon head, standard deviation of the slope gradient (within all cells in a canyon), slope gradient between the canyon head and the canyon foot, and canyon overall rugosity. - Shape metrics: canyon area, number of branches, length/width ratio of the smallest bounding rectangle, border index, compactness and canyon volume. - Location metrics: depth of the canyon head, depth range between the canyon's head and foot, canyon density, distance to coast, distance to the shelf break, incision depth (shelf-incising canyons only), and incision area (shelf-incising canyons only). The hierarchal agglomerative clustering technique was used for the unsupervised classifications. After the filtering, a total of 708 submarine canyons were identified for the entire Australian EEZ. Among these 708 canyons, 134 of them incise into continental shelf; the rest are confined in continental slope. For the shelf-incising canyons, the morphometry, shape and location based classifications all resulted in three classes. Combining the three lower level classifications yielded 15 classes. For the slope-confined canyons, the morphometry, shape and location based classifications resulted in three, four and four classes, respectively. Combining the three lower level classifications yielded 37 classes. GeoHab 2013

  • The shallow-water (<160m) marine environment around the Australian research station, Casey station (east Antarctica) is a high use area, frequently visited by both large resupply vessels and smaller workboats conducting scientific research in the area, yet high resolution modern bathymetric data in the area, as well as much of the east Antarctic continental margin, is limited. The Casey area hosts significant levels of biodiversity, but this knowledge is geographically restricted in scope (i.e. shallow depths, close to shore). This biodiversity faces pressures from human activities and effects of climate change, yet extensive knowledge gaps remain, limiting efforts to conserve and manage it effectively. Improved bathymetric surveying in this region will begin to fill these knowledge gaps by conducting representative sampling of both the physical environment and biological communities and reduce the risk to maritime operations in the region. During the period December 2014 to February 2015, a collaborative multibeam survey (Australian Antarctic Division, Royal Australian Navy and Geoscience Australia) was conducted in the shallow-water near-shore regions adjacent to Casey station and covered an area of ca. 28 km2. The survey employed Geoscience Australia's KONGSBERG EM3002 dual head sonar system mounted on an Australian Antarctic Division supplied science workboat, the RV Howard Burton. In total, the surveyed region covered ca. 34 km2, to a maximum depth of ca. 170m. The data was processed in CARIS v8 and a seafloor surface has been gridded at a resolution of 1m. Preliminary field-based interpretation of the submarine geomorphology reveal several dominant geomorphological features which can be simplified into 4 domains as follows: (1) NW and WSW trending fault and channel systems, (2) glacio-fluvial seafloor features (possible terminal moraines) within channel features, (3) bedrock basement highs and (4) `deep isolated basins.

  • Submarine canyons have been recognised as areas of significant ecological and conservation value. In Australia, 713 canyons were mapped and classified in terms of their geomorphic properties. Many of them are identified as Key Ecological Features (KEFs) and protected by Commonwealth Marine Reserves (CMRs) using expert opinion based on limit physical and ecological information. The effectiveness of these KEFs and CMRs to include ecologically significant submarine canyons as prioritised conservation areas needs to be objectively examined. This study used two local-based spatial statistical techniques, Local Moran's I (LMI) and the Gi* statistic, to identify hotspots of Australian canyons (or unique canyons) for conservation priority. The hotspot analysis identified 29 unique canyons according to their physical attributes that have ecological relevance. Most of these unique physical canyons are distributed on the southern margins. Twenty-four of the 29 canyons are enclosed by the existing KEFs and protected by CMRs to varied extents. In addition, the hotspot analysis identified 79 unique canyons according to their chlorophyll a concentrations, all of which are located in the South-east marine planning region. The findings can be used to update or revise the profile descriptions for some existing KEFs. In future, if the boundaries of these KEFs are deemed necessary to be reviewed, the new information and knowledge could also be used to enhance the conservation priorities of these KEFs.

  • The Leeuwin Current has significant ecological impact on the coastal and marine ecosystem of south-western Australia. This study investigated the spatial and temporal dynamics of the Leeuwin Current using monthly MODIS SST dataset between July 2002 and December 2012. Topographic Position Index layers were derived from the SST data for the mapping of the spatial structure of the Leeuwin Current. The semi-automatic classification process involves segmentation, 'seeds' growing and manual editing. The mapping results enabled us to quantitatively examine the current's spatial and temporal dynamics in structure, strength, cross-shelf movement and chlorophyll a characteristic. It was found that the Leeuwin Current exhibits complex spatial structure, with a number of meanders, offshoots and eddies developed from the current core along its flowing path. The Leeuwin Current has a clear seasonal cycle. During austral winter, the current locates closer to the coast (near shelf break), becomes stronger in strength and has higher chlorophyll a concentrations. While, during austral summer, the current moves offshore, reduces its strength and chlorophyll a concentrations. The Leeuwin Current also has notable inter-annual variation due to ENSO events. In El Niño years the current is likely to reduce strength, move further inshore and increase its chlorophyll a concentrations. The opposite occurs during the La Niña years. In addition, this study also demonstrated that the Leeuwin Current has a significantly positive influence over the regional nutrient characteristics during the winter and autumn seasons.

  • This study explored the full potential of high-resolution multibeam data for an automatic and accurate mapping of complex seabed under a predictive modelling framework. Despite of the extremely complex distributions of various hard substrata at the inner-shelf of the study area, we achieved a nearly perfect prediction of 'hard vs soft' classification with an AUC close to 1.0. The predictions were also satisfactory for four out of five sediment properties, with R2 values range from 0.55 to 0.73. In general, this study demonstrated that both bathymetry and backscatter information (from the multibeam data) should be fully utilised to maximise the accuracy of seabed mapping. From the modelled relationships between sediment properties and multibeam data, we found that coarser sediment generally generates stronger backscatter return and that deeper water with its low energy favours the deposition of mud content. Sorting was also found to be a better sediment composite property than mean grain size. In addition, the results proved one again the advantages of applying proper feature extraction approaches over original backscatter angular response curves.

  • As part of Geoscience Australia's commitment towards the National Environmental Programme's Marine Biodiversity Hub, we have developed a fully four-dimensional (3D x time) Lagrangian biophysical dispersal model to simulate the movement of marine larvae over large, topographically complex areas. The model operates by fusing the results of data-assimilative oceanographic models (e.g. BLUELink, HYCOM, ROMS) with individual-based particle behaviour. The model uses parallel processing on Australia's national supercomputer to handle large numbers of simulated larvae (on the order of several billion), and saves positional information as points within a relational database management system (RDBMS). The model was used to study Australia's northwest marine region, with specific attention given to connectivity patterns among Australia's north-western Commonwealth Marine Reserves and Key Ecological Features (KEFs). These KEFs include carbonate terraces, banks and reefs on the shelf that support diverse benthic assemblages of sponges and corals, and canyons that extend from the shelf edge to the continental slope and are potential biodiversity hotspots. We will show animations of larval movement near canyons within the Gascoyne CMR; larval dispersal probability clouds partitioned by depth and time; as well as matrices of connectivity values among features of interest. We demonstrate how the data can be used to identify connectivity corridors in marine environments, and how the matrices can be analysed to identify key connections within the network. Information from the model can be used to inform priorities for monitoring the performance of reserves through examining net contributions of different reserves (i.e. are they sources or sinks), and studying changes in connectivity structure through adding and removing reserve areas.