<div>The Abbot Point to Hydrographers Passage bathymetry survey was acquired for the Australian Hydrographic Office (AHO) onboard the RV Escape during the period 6 Oct 2020 – 16 Mar 2021. This was a contracted survey conducted for the Australian Hydrographic Office by iXblue Pty Ltd as part of the Hydroscheme Industry Partnership Program. The survey area encompases a section of Two-Way Route from Abbot Point through Hydrographers Passage QLD. Bathymetry data was acquired using a Kongsberg EM 2040, and processed using QPS QINSy. The dataset was then exported as a 30m resolution, 32 bit floating point GeoTIFF grid of the survey area.</div><div>This dataset is not to be used for navigational purposes.</div>

This dataset contains processed and raw backscatter data in matlab format produced by the CMST-GA MB Toolbox from various swath surveys in and around Australian waters.

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.

Geoscience Australia (GA) has an active research interest in using multibeam bathymetry, backscatter data and their derivatives together with geophysical data, sediment samples, biological specimens and underwater video/still footage to create seabed habitat maps. This allows GA to provide spatial information about the physical and biological character of the seabed to support management of the marine estate. The main advantage of using multibeam systems over other techniques is that they provide spatially continuous maps that can be used to relate to physical samples and video observations. Here we present results of a study that aims to reliably and repeatedly delineate hard and soft seabed substrates using bathymetry, backscatter and their derivatives. Two independent approaches to the analysis of multibeam data are tested: (i) a two-stage classification-based clustering method, based solely on acoustic backscatter angular response curves, is used to derive a substrate type map. (ii) a prediction-based classification is produced using the Random Forest method based on bathymetry, backscatter data and their derivatives, with support from video and sediment data. Data for the analysis were collected by Geoscience Australia and the Australian Institute of Marine Science on the Van Dieman Rise in the Timor Sea using RV Solander. The mapped area is characterised by carbonate banks, ridges and terraces that form hardground with patchy sediment cover, and valleys and plains covered by muddy sediment. Results from the clustering method of hard and soft seabed types yielded classification accuracies of 78 - 87% when evaluated against seabed types as observed in underwater video. The prediction-based approach achieved a classification accuracy of 92% based on 10-fold cross-validation. These results are consistent with the current state of knowledge on geoacoustics. Patterns associated with geomorphic facies and biological categories are also observed. These results demonstrate the utility of acoustic data to broadly and objectively characterise the seabed substrate and thereby inform our understanding of the distribution of key habitat types.

The new acquisition of multibeam bathymetry data along with potential field, seismic data and sediment and rock samples has provided a large quantity of new data in the Northern Lord Howe Rise. A detailed study of the relationships between the surface and sub-surface features over the Capel and Faust basins suggests that seafloor deformation is linked to the underlying basement architecture. Numerous seafloor and sub-surface geological features have been identified and mapped over the study area. Their nature, distribution and relationships have been analysed to propose their formative mechanisms. Most of these features are related to buried igneous intrusions and fluid flow either located within depocentre megasequences or along basement bounding faults. The co-genetic geological features indicate that fluid flow is mainly driven by igneous activity. The ongoing fluid flows, after each magmatic pulse has re-utilised pre-existing fluid conduits. Major depocentres have been identified over the study area and could be prospective for petroleum exploration. Potential source, reservoir and seal rocks are likely to be present in the capel and Faust basins. Volcanic activity has driven the geology and fluid flow over the study area since at least the Upper Cretaceous and has to be considered when assessing the petroleum prospectivity of the Capel and Faust basins and also elsewhere in the Lord Howe Rise.

Geoscience Australia provides spatial information of seabed environment to support Australian marine zone management. Central to this approach is the prediction of Australia's seabed biodiversity from spatially continuous data of seabed biophysical properties. Seabed hardness is an important environmental property for predicting marine biodiversity and is often inferred from multibeam backscatter data. Although seabed hardness can be measured based on video images, they are only available at a limited number of sampled locations. In this study, we attempt to predict the spatial distribution of seabed hardness using random forest based on video classification and available marine environmental properties. We illustrate the effects of cross-validation methods including a new cross-validation function on the selection of optimal predictive models. We also test the effects of various predictor sets on the predictive accuracy. This study provides an example for predicting the spatial distribution of environmental properties using random forest in R.

Short contribution to "Atlas of Submarine Glacial Landforms"

Lord Howe Rise is a deep sea marginal plateau located in the Coral Sea and Tasman Sea, ~125,000 km2 in area and 750 to 1200 m in water depth. An area of the western flank of northern Lord Howe Rise covering ~25,500 km2 was mapped and sampled by Geoscience Australia in 2007 to characterise the deep sea environments and benthic habitats. Geomorphic features in the survey area include ridges, valleys, plateaus and basins. Smaller superimposed features include peaks, moats, holes, polygonal furrows, scarps and aprons. The physical structure and biological composition of the seabed was characterised using towed video and sampling of epifaunal and infaunal organisms. These deep sea environments are dominated by thick depositional soft-sediments (sandy mud), with local outcrops of volcanic rock and mixed gravel-boulders. Ridge, valley and plateau environments were moderately bioturbated but few organisms were directly observed or collected. Volcanic peaks were bathymetrically complex hard-rock structures that supported sparse distributions of suspensions feeders (e.g. cold water corals and glass sponges) and associated epifauna (e.g. crinoids and brittlestars). Isolated outcrops along the sloping edge of one ridge also supported similar assemblages, some with high localised densities of coral-dominated assemblages.

The Queen Charlotte Fault (QCF) off western Canada is the northern equivalent to the San Andreas Pacific - America boundary. Geomorphology and surface processes associated with the QCF system have been revealed in unprecedented detail by recent seabed mapping surveys. The QCF bisects the continental shelf of British Columbia forming a fault-valley that is visible in multibeam sonar bathymetry data. The occurrence of the fault within a valley, and its association with what appear to be graben structures, suggest the fault may exhibit minor rifting (extension) as well as strike-slip motions in the region offshore from Haida Gwaii (Queen Charlotte Islands). Fault-valley formation, slumping and stranding of submarine canyon thalwegs are geomorphic expressions of QCF tectonism, illustrating the general applications of multibeam technology to marine geophysical research.

The Carnarvon shelf at Point Cloates, Western Australia, is characterised by a series of prominent ridges and hundreds of mounds that provide hardground habitat for coral and sponge gardens. The largest ridge is 20 m high, extends 15 km alongshore in 60 m water depth and is interpreted as a drowned fringing reef. To landward, smaller ridges up to 1.5 km long and 16 m high are aligned to the north-northeast and are interpreted as relict aeolian dunes. Mounds are less than 5 m high and may also have a sub-aerial origin. In contrast, the surrounding seafloor is sandy with relatively low densities of epibenthic organisms. The dune ridges are estimated to be Late Pleistocene in age and their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the postglacial marine transgression. On the outer shelf, sponges grow on isolated low profile ridges at ~85 m and 105 m depth and are also interpreted as partially preserved relict shorelines.