Securing Antarctica’s Environmental Future (SAEF) is an Australian Research Council Special Research Initiative involving Australian and international universities and partner organisations. The scope of SAEF is broad, with three themes (1) climate processes and change, (2) biodiversity status and trends, and (3) environmental stewardship. Assessing the vulnerability of the Antarctic Ice Sheet in a warming climate is a focus of Theme 1 with objectives including (a) reconstructing past glacier behaviour to assess whether the current retreat is exceptional, or within the realm of natural variability, and to identify thresholds for future ice loss; (b) improving constraints on modern ice sheet boundary conditions and processes such as continental shelf, sub-glacial and sub-ice shelf topography, variability in snow accumulation, ice shelf melting and oceanographic processes, and (c) modelling past, present day and future ice sheet response to climate variability and change, including the influence of anthropogenic climate change, tropical-polar connections and high-latitude climate modes on the ice sheet. SAEF Theme 1 considers the entire Antarctic Ice Sheet, but we have a specific focus on the East Antarctic Ice Sheet including Denman and Vanderford glaciers which have experienced rapid grounding line retreat and have potential to contribute significantly to future sea level rise due to the presence of large subglacial basins inland of their current positions. I will summarise our initial findings and future scope of work including fresh insights into (1) the past behaviour of the East Antarctic Ice Sheet during warm interglacials, and from the Last Glacial Maximum leading into the preindustrial period, (2) the impacts of climate variability including the El Niño Southern Oscillation and the Southern Annular Mode on snow accumulation and surface melt in Antarctica, and (3) preliminary modelling to assess the vulnerability of the ice sheet to climate warming.

The Southern Ocean surrounding Antarctica is a region that is key to a range of climatic and oceanographic processes with worldwide effects, and is characterised by high biological productivity and biodiversity. Since 2013, the International Bathymetric Chart of the Southern Ocean (IBCSO) has represented the most comprehensive compilation of bathymetry for the Southern Ocean south of 60°S. Recently, the IBCSO Project has combined its efforts with the Nippon Foundation – GEBCO Seabed 2030 Project supporting the goal of mapping the world’s oceans by 2030. New datasets initiated a second version of IBCSO (IBCSO v2). This version extends to 50°S (covering approximately 2.4 times the area of seafloor of the previous version) including the gateways of the Antarctic Circumpolar Current and the Antarctic circumpolar frontal systems. Due to increased (multibeam) data coverage, IBCSO v2 significantly improves the overall representation of the Southern Ocean seafloor and resolves many submarine landforms in more detail. This makes IBCSO v2 the most authoritative seafloor map of the area south of 50°S.

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO 2 has been absorbed by the global oceans. Average surface seawater pH levels have already decreased by 0.1 and are projected to decline by ~0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO 3 ) dissolves, likely increasing the vulnerability of many resident marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO 3 mineral phases such as aragonite and high-Mg calcite (HMC). Ocean warming could further exacerbate the effects of OA in these particular species. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make projections about how OA might affect a broad range of SO taxa. We consider a species' geographic range, skeletal mineralogy, biological traits, and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate illustrates that the response variation is largely dependent on mineralogical composition. Species-specific responses due to mineralogical composition indicate that taxa with calcitic, aragonitic, and HMC skeletons, could be at greater risk to expected future carbonate chemistry alterations, and low-Mg calcite (LMC) species could be mostly resilient to these changes. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits, and physiological processes are also expected to influence species-specific responses.

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, -30% of anthropogenic CO2 has been absorbed by the global oceans. Average surface seawater pH levels have already decreased by 0.1 and are projected to decline by -0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many resident marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). Ocean warming could further exacerbate the effects of OA in these particular species. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make projections about how OA might affect a broad range of SO taxa. We consider a species' geographic range, skeletal mineralogy, biological traits, and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate illustrates that the response variation is largely dependent on mineralogical composition. Species specific responses due to mineralogical composition indicate that taxa with calcitic, aragonitic, and HMC skeletons, could be at greater risk to expected future carbonate chemistry alterations, and low-Mg calcite (LMC) species could be mostly resilient to these changes. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits, and physiological processes are also expected to influence species-specific responses.

Abstract The Cape Darnley region in East Antarctica has been an area of scientific interest for a variety of disciplines over the last three decades. The recent acquisition of several high-resolution bathymetry datasets enabled the compilation of a detailed regional bathymetry grid. We present a high-resolution bathymetric compilation of the Cape Darnley region in East Antarctica, including areas of the Mac.Robertson Land shelf, slope and adjacent deep sea. A variety of data, single-beam and multibeam swath bathymetry and digitized depths from nautical charts were sourced from numerous institutions. The 100 m-resolution gridded bathymetric dataset improves previous bathymetric representations of the region and enables visualization of the seafloor morphology in unprecedented detail. The bathymetry grid has been constructed using a layered hierarchy approach based on the source of each dataset. This data compilation forms important baseline information for a range of scientific applications and end users including oceanographers, glacial modellers, biologists and geologists. The compilation will aid numerical modelling of ocean circulation, reconstruction of palaeo-ice streams and refinement of ice-sheet models.

Abstract. Understanding past retreat of Antarctic ice margins provides valuable insight for predicting how ice sheets may respond to future environmental change. This study, based on high resolution multibeam bathymetry from the nearshore region of the Windmill Islands, East Antarctica, reveals a style of retreat that has been rarely observed on the Antarctic margin. A suite of seafloor features record the final retreat stages of a relatively thin, and increasingly fractured tidewater glacier confined within narrow troughs and embayments, forming a suite of features more typical of warm-based ice, but occurring here in a region of cold-based ice with limited surface meltwater production. The pattern of moraines and crevasse squeeze ridges, reveals strong topographic and substrate control on the nature of ice sheet retreat. Topographic control is indicated by fine-scale variability in the orientation and distribution of glacial landforms, which show that the seabed topography influenced the shape of the ice margin, caused deflection of ice flow and led to the separation of flow downstream from topographic highs. The availability of water saturated marine sediments within the troughs and depressions also had a profound effect on the landform record, facilitating the construction of moraines and crevasse squeeze ridges within topographic lows, corresponding to areas of modern sediment accumulation. Surrounding areas of crystalline bedrock, by contrast, acted as sticky spots and lack a well-developed landform record. This seafloor glacial record emphasises the importance of understanding the bed topography and substrate when predicting the nature of ice margin retreat and provides new perspectives for understanding the stability of the East Antarctic margin.

Shelf-incising canyons on the upper continental slope are important conduits for the export of dense, organic-rich shelf waters from the East Antarctic margin. This interaction of geomorphic features and oceanography plays an important role in controlling benthic community composition in this environment. Dense hydrocoral-sponge communities have been identified at new sites within a shelf-incising canyon on the upper continental slope (430-640 m) off George V Land, East Antarctica, adjacent to sites previously identified and declared Vulnerable Marine Ecosystems by the Commission for the Conservation of Antarctic Marine Living Resources. Sparse hydrocoral communities were also found at several sites along the continental slope receiving dense shelf waters. These findings provide further evidence of hydrocoral communities along the George V Land slope and support previous hypotheses regarding the importance of Antarctic Bottom Water export from the shelf providing an abundant food source for the benthos within shelf-incising canyons.

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO 2 has been absorbed by the oceans. Seawater pH levels have already decreased by 0.1 and are predicted to decline by ~ 0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO 3 ) dissolves, likely increasing the vulnerability of many marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO 3 mineral phases such as aragonite and high-Mg calcite (HMC). These negative effects may become even exacerbated by increasing sea temperatures. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make predictions about how OA might affect different taxa. We consider their geographic range, skeletal mineralogy, biological traits and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate shows response variation depending on mineralogical composition. Species-specific responses due to mineralogical composition suggest taxa with calcitic, aragonitic and HMC skeletons may be more vulnerable to the expected carbonate chemistry alterations, and low magnesium calcite (LMC) species may be mostly resilient. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits and physiological processes are also expected to influence species specific responses.

A high-resolution multibeam sonar dataset covering an area of ca. 33km2 was collected in the vicinity of the Windmill Islands (67°S, 110°E), Wilkes Land, East Antarctica. The new data permit visualisation of the nearshore seafloor morphology in unprecedented detail, providing invaluable insight into the ice-sheet history of the region. A range of geomorphic features are evident, including prominent parallel northwest-trending linear fault sets affecting Mesoproterozoic metamorphic basement, which appear to control the regional coastal physiography. The fault systems probably formed during fragmentation of eastern Gondwana during the Mesozoic. Networks of sub-glacial meltwater channels, preserved on bedrock platforms and ridges, indicate grounding of a thick ice sheet over the continental shelf during previous glaciations. West-trending 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. The direction of these features coincides with glacial striae on onshore crystalline bedrock outcrops. Perhaps the most striking glacial geomorphological features are sets of arcuate ridges confined mostly within glacially excavated U-shaped troughs formed by erosion of the northwest-trending 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 of the Law Dome margin. This event was possibly triggered in response to local environmental forcing during the mid-late Holocene. Minor post-glacial marine sedimentation is preserved in several small (≤1km2) isolated basins with shallow seaward sills.

Streamlined subglacial sediments are common in seafloor bathymetric images from many glaciated margins. Less common are seafloor features left by cold-based ice. The shallow waters around the now largely ice-free Vestfold Hills in East Antarctica (Fig. 1a, e) show few streamlined sedimentary features, even though the area has clearly been glaciated as implied by striated bedrock, moraine ridges and abundant erratic boulders on adjacent exposed land. A likely explanation for the absence of streamlined subglacial landforms is that the area was glaciated by ice frozen to its bed. Fig. 1. Multibeam swath bathymetry, outcrop photo and topographic profiles of boulder-rich debris mantle and sand ribbons from the Vestfold Hills coastal zone, East Antarctica. ( a ) Sun-illuminated bathymetric image of Airport Beach Embayment showing the debris mantle. Ice-keel ploughmarks are shown outside the embayment. Acquisition system Kongsberg EM3002. Frequency 300 kHz. Grid-cell size 2 m. ( b ) Close-up of debris mantle showing individual boulders. ( c ) Photograph of bouldery debris mantle above sea level. Large boulder is 4 m in diameter. ( d ) Multibeam image of sand ribbons and boulders. ( e ) Location of study area (red …

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 km(2) 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 with only weak 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 seafloor 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. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

Abstract A survey of nearshore areas in the Vestfold Hills, Antarctica, using high-resolution multibeam swath bathymetry provided both a detailed digital bathymetric model and information on sediment acoustic backscatter. Combined with underwater video transects and sediment sampling, these data were used to identify and map geomorphic units. Six geomorphic units identified in the survey region include: rocky outcrops, basins, pediments, valleys, scarps and embayments. In addition to geomorphic units, the data revealed sedimentary features that provide insights into post-glacial sediment transport and erosion in the area. Ice keel pits and scours are common, and sea floor channels, scour depressions and sand ribbons indicate transport and deposition by wind-driven currents and oceanographic circulation. Gullies and sediment lobes observed on steep slopes indicate mass movement of sediment. Some of these processes have not been directly observed to date, but their effectiveness in shaping the modern sea floor is clearly indicated by the sea floor mapping data. The embayments preserve a mantle of boulder sand probably deposited by cold-based glaciers which were flanked by faster-flowing ice in adjoining regions.

Increases in atmospheric CO2 cause the oceanic surface water to continuously acidify, which has multiple and profound impacts on coastal and continental shelf environments. Here we present the carbonate mineral composition in surface sediments from a range of continental shelf seabed environments and their current and predicted stability under ocean acidifying conditions. Samples come from the following four tropical Australian regions: (1) Capricorn Reef (southern end of the Great Barrier Reef), (2) the Great Barrier Reef Lagoon, (3) Tones Strait, and (4) the eastern Joseph Bonaparte Gulf. Beyond the near-shore zone, these regions typically have a carbonate content in surface sediments of 80 wt % or more. The abundance of high-magnesium calcites (HMC) dominates over aragonite (Arag) and low-magnesium calcite (LMC) and constitutes between 36% and 50% of all carbonate. HMC, with a magnesium content larger than 8-12 mol %, is more soluble than both Arag and LMC, and the solubility of HMC positively correlates with its magnesium concentration. From the solubility data of Plummer and Mackenzie (Am. J. Sci. 1974, 274, 61-83), 95% of HMC in the four regions is presently in metastable equilibrium relative to global mean tropical sea surface water. HMC is predicted to become destabilized in the four regions between 2040 and 2080 AD, with typical HMC decline rates between 2% and 5% per year. The range of respective estimated carbonate dissolution rates is expected to exceed current continental shelf carbonate accumulation rates, leading to net dissolution of carbonate during the period of HMC decline. In a geological context, the decline in HMC in tropical continental shelf environments is a global event triggered by reaching below-equilibrium conditions. The characteristic change in carbonate mineral composition in continental shelf sediments will serve as a geological marker for the proposed Anthropocene Epoch.

Dense shelf water formed in the Mertz Polynya supplies the lower limb of the global overturning circulation, ventilating the abyssal Indian and Pacific Oceans. Calving of the Mertz Glacier Tongue (MGT) in February 2010 altered the regional distribution of ice and reduced the size and activity of the polynya. The salinity and density of dense shelf water declined abruptly after calving, consistent with a reduction of sea ice formation in the polynya. Breakout and melt of thick multiyear sea ice released by the movement of iceberg B9B and the MGT freshened near-surface waters. The input of meltwater likely enhanced the availability of light and iron, supporting a diatom bloom that doubled carbon uptake relative to precalving conditions. The enhanced biological carbon drawdown increased the carbonate saturation state, outweighing dilution by meltwater input. These observations highlight the sensitivity of dense water formation, biological productivity, and carbon export to changes in the Antarctic icescape. Citation: Shadwick, E. H., S. R. Rintoul, B. Tilbrook, G. D. Williams, N. Young, A. D. Fraser, H. Marchant, J. Smith, and T. Tamura (2013), Glacier tongue calving reduced dense water formation and enhanced carbon uptake, Geophys. Res. Lett., 40, 904-909, doi:10.1002/grl.50178.

The Vestfold Hills is an area of ice-free coast in East Antarctica. The coast is a complex of small islands, embayments, and fjords. Most of the coast is rocky, but a few sandy beaches are present. Water depths vary from 0 to 200 m in the survey area. High-resolution multibeam bathymetry, underwater video, and detailed diving surveys reveal a mosaic of rock outcrops, sediment-covered basins, and transition zones similar to pediments of desert landscapes. Iceberg scouring is common, but some areas are protected by peninsulas and islands. Biological communities are controlled by substrate and light level, with rocky substrates in shallow water, where ice-free conditions persist for most of the summer, dominated by macroalgae. Areas of sediment have invertebrate fauna and some macroalgae. Rocky areas in deep water or where sea ice persists through the summer are invertebrate dominated.