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International conservation goals have been set to mitigate Southern Ocean ecosystem deterioration, with multiple monitoring programs evaluating progress towards those goals. The scale of continuous monitoring through visual observations, however, is challenged by the remoteness of the area and logistical constraints. Given the ecological and economic importance of the Southern Ocean, it is imperative that additional biological monitoring approaches are explored. Recently, marine sponges, which are frequently caught and discarded in Southern Ocean fisheries, have been shown to naturally accumulate environmental DNA (eDNA). Here, we compare fish eDNA signals from marine sponge bycatch specimens to fish catch records for nine locations on the continental shelf (523.5–709 m) and 17 from the continental slope (887.5–1611.5 m) within the Ross Sea, Antarctica. We recorded a total of 20 fishes, with 12 fishes reported as catch, 18 observed by eDNA, and ten detected by both methods. While sampling location was the largest contributor to the variation observed in the dataset, eDNA obtained significantly higher species richness and displayed a significantly different species composition compared to fish catch records. Overall, eDNA read count correlated more strongly with fish abundance over biomass. Species composition correlated on a regional scale between methods, however eDNA signal strength was a low predictor of catch numbers at the species level. Our results highlight the potential of sponge eDNA monitoring in the Southern Ocean by detecting a larger fraction of the fish community compared to catch recordings, thereby increasing our knowledge of this understudied ecosystem and, ultimately, aiding conservation efforts. [ABSTRACT FROM AUTHOR]

Hydrozoans are recognized as one of the main and most characteristic zoological groups of the Antarctic benthos, despite the fact that there are still large Antarctic areas where the hydrozoan fauna is completely unknown or poorly known (e.g., the Admunsen Sea and Mary Byrd Land, in West Antarctica, and Queen Maud Land and Enderby Land, in East Antarctica). The present study contributes to a better understanding of the Ross Sea benthic hydroid fauna by studying material collected through several New Zealand expeditions mostly with RV Tangaroa. The Ross Sea includes the world's largest marine-protected area (MPA) and is of considerable biological value and importance for scientific research. Although some parts of the Ross Sea shelf have been intensively sampled, others have not, including deeper parts of the continental shelf and the slope. Forty species were found, belonging to 15 families and 19 genera. Six species, including Eudendrium megaloarmatus sp. nov., Nemertesia gelida sp. nov., Schizotricha frigida sp. nov., Symplectoscyphus pseudofrondosus sp. nov. and Symplectoscyphus tortuosus sp. nov., represent new records, bringing the number of known species in the Ross Sea to 84. Leptothecata is dominant, with 35 species, while Anthoathecata is represented by five species. Symplectoscyphidae is the most diversified family with 12 species (30%), and Symplectoscyphus is the most speciose genus with nine species (23%). Three main hydroid assemblages have been found in the studied area, two with a wide bathymetric range and relatively high species diversity, and a third with a narrow and deep bathymetric range and remarkably low hydroid diversity. The hydroid fauna is dominated by species with a wide bathymetric distribution and virtually all species are restricted to Antarctic or Antarctic/sub-Antarctic waters, with 70% endemic to the Antarctic region. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Current is guided by the topographic gradient of the Antarctic continental slope and creates a dynamical barrier between the continental shelf and the open ocean. The current's vertical structure varies around the continent affecting cross‐slope water mass exchange with consequences for Antarctic mass loss, ventilation of the deep ocean, and carbon uptake. The Antarctic Slope Current is surface‐intensified in many regions but bottom‐intensified in regions of dense overflows. This study investigates the role of dense overflows in modifying the dynamics of the bottom‐intensified flow using a 0.1° global ocean‐sea ice model. The occurrence of bottom‐intensification is tightly linked with dense overflows and bottom speeds correlate with dense overflows on interannual time scales. A lack of vertical connectivity between the bottom and surface flow, however, suggests that the along‐slope bottom water flows are coincidentally co‐located with the Antarctic Slope Current, rather than dynamically a part of the current. Plain Language Summary: The Antarctic Slope Current is a narrow ocean current that travels around Antarctica following the continental slope. It separates the shallow and cold continental shelf from much warmer waters in the open ocean. Intrusions of the relatively warm water across the continental slope impacts melting of Antarctic ice shelves and global sea level rise. Understanding what controls the strength and variability of the Antarctic Slope Current is therefore important. The Antarctic Slope Current usually has the largest velocities near the surface, but there are regions where there is also a strong bottom flow. We use a coupled ocean‐sea ice model and show that the bottom flow is controlled by the export of very dense shelf water that flows down the continental slope in a few locations around the continent. However, the bottom and surface flow does not vary together on interannual time scales which tells us that the two components of the Antarctic Slope Current are largely independent. The result is important as the formation of dense shelf water is expected to reduce in the future which will impact the deep flow, but not the surface component. Key Points: Simulations reveal a close spatial relationship between the bottom‐intensified Antarctic Slope Current and Dense Shelf Water exportInterannual variability of Dense Shelf Water is reflected in the bottom speed of the bottom‐intensified Antarctic Slope CurrentThe surface component varies independently from the bottom‐intensified flow implying two distinct, co‐located currents [ABSTRACT FROM AUTHOR]

Active continental margins are tectonic sites with complex sedimentary processes. Tectono–sedimentary interactions occur over geological time and determine the modern morphology of the margin. However, such interactions have been poorly documented in high‐latitude regions. This study focuses on deep‐water sedimentary systems on the South Shetland convergent margin, which is the only remaining active continental margin in Antarctica. Numerous gullies, 20 canyons and three contourite drifts are identified by interpreting bathymetry, oceanography and reflection seismic data. Heavy mineral contents of a gravity core, located at a downslope elongated mounded drift, show the asynchronous interplay of downslope and alongslope processes. The rest of the margin is dominated by turbidity currents. Variations in the slope gradient control thalweg profiles and sinuosity of canyons. Tectonic‐related morphology restricts the distribution of contourite drifts. Earthquakes triggered by underplating and tectonic compression may induce slope instability at the lower flank of the plastered drift. Tectonic uplift influences the amount of sediments transported by ice sheets and controls the shelf stacking pattern. The mixed turbidite–contourite system transitions to separated canyon and drift systems from passive to active continental margins under the influence of the tectonic‐related morphology. A systematic comparison has been made among several convergent margins with similar tectonic settings. Results suggest that submarine canyons on these shelf‐slope systems have similar morphological features and are comparable in size. Coarse sediment input and steep continental slopes (mean slope 7 to 10°) control the canyon morphology on these margins. Therefore, this research has important implications for furthering the current understanding of sedimentary systems on high‐latitude convergent margins and tectono–sedimentary interactions. [ABSTRACT FROM AUTHOR]

Simple Summary: Patagonian moray cod is known to inhabit the cold waters near Antarctica, and it belongs to the Muraenolepis genus. This genus has seven species, and five of them are recently reported. The Muraenolepis genus has similar morphological characters, and this is a limitation of taxonomical classification. In this study, a genome survey and microsatellite marker analysis were conducted to characterize the genome profile for classification. As a result, genomic data such as genome size and microsatellite motifs were obtained. The Muraenolepididae family of fishes, known as eel cods, inhabits continental slopes and shelves in the Southern Hemisphere. This family belongs to the Gadiformes order, which constitutes one of the most important commercial fish resources worldwide, but the classification of the fish species in this order is ambiguous because it is only based on the morphological and habitat characteristics of the fishes. Here, the genome of Patagonian moray cod was sequenced using the Illumina HiSeq platform, and screened for microsatellite motifs. The genome was predicted to be 748.97 Mb, with a heterozygosity rate of 0.768%, via K-mer analysis (K = 25). The genome assembly showed that the total size of scaffolds was 711.92 Mb and the N50 scaffold length was 1522 bp. Additionally, 4,447,517 microsatellite motifs were identified from the genome survey assembly, and the most abundant motif type was found to be AC/GT. In summary, these data may facilitate the identification of molecular markers in Patagonian moray cod, which would be a good basis for further whole-genome sequencing with long read sequencing technology and chromosome conformation capture technology, as well as population genetics. [ABSTRACT FROM AUTHOR]

Warm deep water intrusion over the Antarctic continental shelves threatens the Antarctic ice sheet stability by enhancing the basal melting of ice shelves. In East Antarctica, the Antarctic Slope Current (ASC), along with the Antarctic Slope Front (ASF), acts as a potential vorticity barrier to prevent the warm modified Circumpolar Deep Water (mCDW) from ventilating the cold and fresh shelf. However, mCDW onshore transport is still observed within certain shelf regions, such as submarine troughs running perpendicular to the continental shelf. This study focuses on the dynamic mechanisms governing mCDW intrusion within a submarine trough over the fresh shelf regions, East Antarctica. Based on an idealized eddy-resolving coupled ocean–ice shelf model, two high-resolution process-oriented numerical experiments are conducted to reveal the mechanisms responsible for the mCDW onshore transport. Three dynamic mechanisms governing cross-slope mCDW intrusion are identified: 1) the bottom pressure torque, 2) the topography beta spiral, and 3) the topography Rossby waves. These three mechanisms simultaneously govern the mCDW intrusion together. The bottom pressure torque plays a leading role in driving the time-mean onshore flow whose vertical structure is determined by the topography beta spiral, while the topography Rossby waves contribute to the high-frequency oscillations in the onshore volume and heat transport. The simulated spatial distribution and seasonality of mCDW intrusion qualitatively coincide with the observed mCDW intrusion over fresh shelf regions, East Antarctica. Both the topography beta spiral and the ASC play an important role in governing the seasonality of mCDW intrusion. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Current (ASC) circumnavigates the Antarctic continent following the continental slope and separating the waters on the continental shelf from the deeper offshore Southern Ocean. Water mass exchanges across the continental slope are critical for the global climate as they impact the global overturning circulation and the mass balance of the Antarctic ice sheet via basal melting. Despite the ASC's global importance, little is known about its spatial and subannual variability, as direct measurements of the velocity field are sparse. Here, we describe the ASC in a global eddying ocean–sea ice model and reveal its large-scale spatial variability by characterizing the continental slope using three regimes: the surface-intensified ASC, the bottom-intensified ASC, and the reversed ASC. Each ASC regime corresponds to a distinct classification of the density field as previously introduced in the literature, suggesting that the velocity and density fields are governed by the same leading-order dynamics around the Antarctic continental slope. Only the surface-intensified ASC regime has a strong seasonality. However, large temporal variability at a range of other time scales occurs across all regimes, including frequent reversals of the current. We anticipate our description of the ASC's spatial and subannual variability will be helpful to guide future studies of the ASC aiming to advance our understanding of the region's response to a changing climate. [ABSTRACT FROM AUTHOR]

The article presents data indicating the relationship of the bathymetric distribution of solitary endemic scleractinian corals inhabiting the Antarctic continental shelf and upper continental slope with the vertical density of the Antarctic Circumpolar Current. The study is based on materials collected by expeditions of the Shirshov Institute of Oceanology (IO RAS) and the literature data. The results show that endemic species that appeared in the Late Neogene and Pleistocene were unable to propagate across other oceans due to the existing horizontal and vertical density of the Arctic Circumpolar Current during that period. [ABSTRACT FROM AUTHOR]

Manganese (Mn) is an abundant element in the Earth's crust. However, its concentrations in open ocean seawater are low, where external inputs are scarce. In this study, we report the dissolved Mn and particulate Mn distributions in the Southern Ocean, measured along the GEOTRACES—SR3 transect, from Tasmania (Australia) to Antarctica in the Southern Ocean, during the austral summer 2018. Both dissolved Mn and particulate Mn concentrations were generally low away from localized sources (< 0.3 nmol L−1 and < 0.1 nmol L−1, respectively) along the transect. Our observations of a lower labile particulate fraction than previously measured suggest the Southern Ocean has a unique particulate Mn composition. Low surface dissolved Mn concentrations were attributed to biological uptake and few external sources. Our results suggest biological control of the Mn cycle was higher above the Antarctic continental slope, compared to the rest of the section, and our particulate Mn : P ratios indicated the presence of iron‐stressed diatoms south of the Sub‐Antarctic Front. We suggest low dissolved Mn surface concentrations may (co‐)limit phytoplankton growth in this region. Localized higher dissolved Mn concentrations were observed due to external sources, such as sedimentary and hydrothermal inputs. The presence of an eddy at the same latitude as a hydrothermal plume induced an upwelling of hydrothermally enriched waters up to 1000 m; however, no dissolved Mn inputs to the surface waters were observed. We suggest previous dissolved Mn inputs to the surface layer may be obscured by biological uptake. [ABSTRACT FROM AUTHOR]

Basal melting of Antarctic ice shelves accounts for more than half of the mass loss from the Antarctic ice sheet. Many studies have focused on active basal melting at ice shelves in the Amundsen–Bellingshausen seas and the Totten ice shelf, East Antarctica. In these regions, the intrusion of Circumpolar Deep Water (CDW) onto the continental shelf is a key component for the localized intensive basal melting. Both regions have a common oceanographic feature: southward deflection of the Antarctic Circumpolar Current brings CDW toward the continental shelves. The physical setting of the Shirase Glacier tongue (SGT) in Lützow-Holm Bay corresponds to a similar configuration on the southeastern side of the Weddell Gyre in the Atlantic sector. Here, we conduct a 2–3 km resolution simulation of an ocean–sea ice–ice shelf model using a recently compiled bottom-topography dataset in the bay. The model can reproduce the observed CDW intrusion along the deep trough. The modeled SGT basal melting reaches a peak in summer and a minimum in autumn and winter, consistent with the wind-driven seasonality of the CDW thickness in the bay. The model results suggest the existence of an eastward-flowing undercurrent on the upper continental slope in summer, and the undercurrent contributes to the seasonal-to-interannual variability in the warm water intrusion into the bay. Furthermore, numerical experiments with and without fast-ice cover in the bay demonstrate that fast ice plays a role as an effective thermal insulator and reduces local sea ice formation, resulting in much warmer water intrusion into the SGT cavity. [ABSTRACT FROM AUTHOR]

Large submarine plateaus impede the eastward flow of the deep‐reaching Antarctic Circumpolar Current (ACC), and at the southern Kerguelen Plateau (SKP), the ACC flow is steered north through the Fawn Trough and south through the Princess Elizabeth Trough. During the Kerguelen Axis study, a regional‐scale ecosystem survey, oceanographic sampling showed the ACC water properties west of the SKP to be distinct from those over the SKP. Electrona antarctica, a dominant mesopelagic fish species, is associated with Circumpolar Deep Water transported by the ACC, and modified versions that occur over and downstream from the SKP including along the Antarctic continental slope. Here, otolith chemistry from samples of E. antarctica collected during the survey were used to test a biophysical hypothesis predicting structuring and movement between populations along zonal flow in the ACC. In chemistry deposited during early life in the otolith nuclei, the relationship between MgCa−1 and SrCa−1 showed complete separation between fish collected over the SKP and within the ACC proper, indicating population differentiation. Chemistry from the otolith edges, deposited during the period leading up to capture, showed significantly higher concentrations of MgCa−1 over the SKP, likely related to differences in feeding and reproduction. Fish with nucleus chemistry characteristic of the SKP were also found in samples caught further east, suggesting they were transported along the ACC downstream, and southward toward the Antarctic continent within the Australian–Antarctic Gyre. [ABSTRACT FROM AUTHOR]

The World Ocean is estimated to store more than 90% of the excess energy resulting from man-made greenhouse gas-driven radiative forcing as heat. Uncertainties of this estimate are related to undersampling of the subpolar and polar regions and of the depths below 2000 m. Here we present measurements from the Weddell Sea that cover the whole water column down to the sea floor, taken by the same accurate method at locations revisited every few years since 1989. Our results show widespread warming with similar long-term temperature trends below 700-m depth at all sampling sites. The mean heating rate below 2000m exceeds that of the global ocean by a factor of about 5. Salinity tends to increase--in contrast to other Southern Ocean regions--at most sites and depths below 700 m, but nowhere strongly enough to fully compensate for the warming effect on seawater density, which hence shows a general decrease. In the top 700m neither temperature nor salinity shows clear trends. A closer look at the vertical distribution of changes along an approximately zonal and a meridional section across the Weddell Gyre reveals that the strongest vertically coherent warming is observed at the flanks of the gyre over the deep continental slopes and at its northern edge where the gyre connects to the Antarctic Circumpolar Current (ACC). Most likely, the warming of the interior Weddell Sea is driven by changes of the Weddell Gyre strength and its interaction with the ACC. [ABSTRACT FROM AUTHOR]

The stability of the West Antarctic Ice Sheet (WAIS) depends on ocean heat transport toward its base and remains a source of uncertainty in sea level rise prediction. The Antarctic Slope Current (ASC), a major boundary current of the ocean's global circulation, serves as a dynamic gateway for heat transport toward Antarctica. Here, we use observations collected from the Bellingshausen Sea to propose a mechanistic explanation for the initiation of the westward‐flowing ASC. Waters modified throughout the Bellingshausen Sea by ocean‐sea‐ice and ocean‐ice‐shelf interactions are exported to the continental slope in a narrow, topographically steered western boundary current. This focused outflow produces a localized front at the shelf break that supports the emerging ASC. This mechanism emphasizes the importance of buoyancy forcing, integrated over the continental shelf, as opposed to local wind forcing, in the generation mechanism and suggests the potential for remote control of melt rates of WAIS' largest ice shelves. Plain Language Summary: The Antarctic Slope Current (ASC) is an ocean current that separates warmer, offshore water from colder waters over the continental shelf. The ASC helps to control the movement of warm water on to the continental shelf and ultimately under floating ice shelves. Warm ocean water has contributed to the melting and thinning of West Antarctic ice shelves in recent decades. This study describes where and how the ASC first forms in West Antarctica. Previous studies have suggested that the ASC responds primarily to atmospheric winds blowing over the current itself, whereas here it is argued that processes occurring over a much larger region of the west Antarctic continental shelf may determine the strength and structure of the ASC. These results contribute to our understanding of the long‐term, for example, decades or longer, evolution of the West Antarctic Ice Sheet. Key Points: The initiation of a westward Antarctic Slope Current (ASC) occurs in the western Bellingshausen SeaThe ASC arises from the export of waters, modified by ocean‐ice interactions, to the shelf break, rather than from local wind forcingThis mechanism suggests the potential for remote control of shelf properties as well as West Antarctic ice shelf melt rates [ABSTRACT FROM AUTHOR]

The Antarctic Slope Front (ASF) is located along much of the Antarctic continental shelf break and helps to maintain a barrier to the movement of Circumpolar Deep Water (CDW) onto the continental shelf. The stability of the ASF has a major control on cross-shelf heat transport and ocean-driven basal melting of Antarctic ice shelves. Here, the ASF dynamics are investigated for continental shelves with weak dense shelf water (DSW) formation, which are thought to have a stable ASF, common for regions in East Antarctica. Using an ocean process model, this study demonstrates how offshore bottom Ekman transport of shelf waters leads to the development of a deep bottom mixed layer at the lower continental slope, and subsequently determines an intrinsic variability of the ASF. The ASF variability is characterized by instability events that affect the entire water column and occur every 5-10 years and last for approximately half a year. During these instability events, the cross-shelf density gradient weakens and CDW moves closer to the continent. Stronger winds increase the formation rate of the bottom mixed layer, which causes a subsequent increase of instability events. If the observed freshening trend of continental shelf waters leads to weaker DSW formation, more regions might be vulnerable for the ASF variability to develop in the future. [ABSTRACT FROM AUTHOR]

Variability in the heat delivery by Circumpolar Deep Water (CDW) is responsible for modulating the basal melting of the Amundsen Sea ice shelves. However, the mechanisms controlling the CDW inflow to the region's continental shelf remain little understood. Here, a high-resolution regional model is used to assess the processes governing heat delivery to the Amundsen Sea. The key mechanisms are identified by decomposing CDW temperature variability into two components associated with 1) changes in the depth of isopycnals [heave (HVE)], and 2) changes in the temperature of isopycnals [water mass property changes (WMP)]. In the Dotson--Getz trough, CDW temperature variability is primarily associated with WMP. The deeper thermocline and shallower shelf break hinder CDW access to that trough, and CDW inflow is regulated by the uplift of isopycnals at the shelf break--which is itself controlled by wind-driven variations in the speed of an undercurrent flowing eastward along the continental slope. In contrast, CDW temperature variability in the Pine Island--Thwaites trough is mainly linked to HVE. The shallower thermocline and deeper shelf break there permit CDW to persistently access the continental shelf. CDW temperature in the area responds to wind-driven modulation of the water mass on-shelf volume by changes in the rate of inflow across the shelf break and in Ekman pumping-induced vertical displacement of isopycnals within the shelf. The western and eastern Amundsen Sea thus represent distinct regimes, in which wind forcing governs CDW-mediated heat delivery via different dynamics. [ABSTRACT FROM AUTHOR]

All exchanges between the open ocean and the Antarctic continental shelf must cross the Antarctic Slope Current (ASC). Previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability, yet the mechanisms responsible for setting the ASC's transport and structure have received relatively little attention. In this study the roles of winds, eddies, and tides in accelerating the ASC are investigated using a global ocean–sea ice simulation with very high resolution (1/48° grid spacing). It is found that the circulation along the continental slope is accelerated both by surface stresses, ultimately sourced from the easterly winds, and by mesoscale eddy vorticity fluxes. At the continental shelf break, the ASC exhibits a narrow (~30–50 km), swift (>0.2 m s−1) jet, consistent with in situ observations. In this jet the surface stress is substantially reduced, and may even vanish or be directed eastward, because the ocean surface speed matches or exceeds that of the sea ice. The shelfbreak jet is shown to be accelerated by tidal momentum advection, consistent with the phenomenon of tidal rectification. Consequently, the shoreward Ekman transport vanishes and thus the mean overturning circulation that steepens the Antarctic Slope Front (ASF) is primarily due to tidal acceleration. These findings imply that the circulation and mean overturning of the ASC are not only determined by near-Antarctic winds, but also depend crucially on sea ice cover, regionally-dependent mesoscale eddy activity over the continental slope, and the amplitude of tidal flows across the continental shelf break. [ABSTRACT FROM AUTHOR]

Circumpolar Deep Water (CDW) transport across the Antarctic continental slope regulates the delivery of heat to the shelf and its availability to melt floating ice shelves. The cross‐slope density field, calculated from profiles collected by conductivity‐temperature‐depth‐tagged marine mammals on the East Antarctic slope (0–160°E, above 1,000‐ to 3,000‐m isobaths), indicates eddy‐driven overturning: onshore transport of CDW and offshore transport of shallower Antarctic Surface Water. Enhanced eddy activity, determined by a spice standard deviation threshold in the CDW layer, is present over about a third of the East Antarctic slope analyzed. Significantly stronger CDW transport in regions of elevated spice variability produces subsurface temperature anomalies of 0.2–0.25 °C relative to the East Antarctic average. Estimating eddy diffusivity from the hydrography yields about 0.8 m2/s of warm CDW transport to the shelf break in high‐variability regions. Variability of eddy‐induced CDW transport influences the reservoir of heat available for transport across the shelf break. Plain Language Summary: The transport of warm water from the open ocean to the Antarctic continental shelf has global significance, as it regulates the melt of ice shelves and dense water formation. We quantify the strength of eddy‐driven transport of relatively warm Circumpolar Deep Water (CDW) across the continental slope of East Antarctica from the observed cross‐slope density structure. We find that, in general, there is an eddy‐driven overturning: deeper CDW is transported onshore while shallower Antarctic Surface Water is transported offshore. Upon closer inspection, we find that regions with elevated temperature and salinity variability on density surfaces are associated with significantly stronger onshore transport of CDW by eddies. These hot spots of eddy transport produce warm and salty anomalies at the shelf break, impacting the reservoir of heat available to the shelf. Key Points: Cross‐slope eddy transport is inferred from observed density‐layer thickness gradients in East Antarctica between 0°E and 160°EEnhanced onshore transport (≈1.5 × East Antarctic mean) of warm, salty Circumpolar Deep Water occurs in regions of high isopycnal spice variabilityEddy‐induced overturning carries ≈0.8 m2/s of CDW poleward to produce warm, salty anomalies at the shelf break in eddying regions [ABSTRACT FROM AUTHOR]

To investigate the cross-slope freshwater exchange in the Australian-Antarctic Basin between 80 and 150°E, the stable oxygen isotopic ratio (δ18O) was evaluated based on top-to-bottom hydrographic sections by R/V Kaiyo-Maru in 2018/2019 summer. The southern flank of the Antarctic Circumpolar Current (ACC) flows eastward in the north and the Antarctic Slope Current (ASC) flows westward along the continental slope in the south of the analysis domain. Continental shelf regions including the area off Sabrina Coast were also studied. We obtained the spatial δ18O structure characteristics of water masses that were transformed by freshwater input from the highest Circumpolar Deep-Water value. δ18O-salinity relationship in the near-surface layer revealed a regional difference between the upper and lower continental slopes. The fractions of sea ice melt and meteoric water were estimated using mass-balance calculations assuming constant endmembers with no spatial and temporal variabilities. The fraction of sea ice meltwater was usually highest at the surface and rapidly decreased to the temperature minimum layer, while the meteoric water fraction was also highest at the surface, gradually decreasing to the temperature maximum layer. The meteoric water fraction is usually high on the upper slope and continental shelf. The area-average of sea ice meltwater integrated above the temperature minimum is about 0.7 m water-equivalent, with large accumulation off and downstream of the coastal polynyas. Given the projected future glacial ice discharge and sea ice cover changes, repeated δ18O measurement is crucial to implicate the future response of the freshwater cycle closer to the Antarctic continental shelf. [ABSTRACT FROM AUTHOR]

Along various stretches of the Antarctic margins, dense Antarctic Bottom Water (AABW) escapes its formation sites and descends the continental slope. This export necessarily raises the isopycnals associated with lighter density classes over the continental slope, resulting in density surfaces that connect the near-freezing waters of the continental shelf to the much warmer circumpolar deep water (CDW) at middepth offshore. In this article, an eddy-resolving process model is used to explore the possibility that AABW export enhances shoreward heat transport by creating a pathway for CDW to access the continental shelf without doing any work against buoyancy forces. In the absence of a net alongshore pressure gradient, the shoreward CDW transport is effected entirely by mesoscale and submesoscale eddy transfer. Eddies are generated partly by instabilities at the pycnocline, sourcing their energy from the alongshore wind stress, but primarily by instabilities at the CDW-AABW interface, sourcing their energy from buoyancy loss on the continental shelf. This combination of processes induces a vertical convergence of eddy kinetic energy and alongshore momentum into the middepth CDW layer, sustaining a local maximum in the eddy kinetic energy over the slope and balancing the Coriolis force associated with the shoreward CDW transport. The resulting slope turbulence self-organizes into a series of alternating along-slope jets with strongly asymmetrical contributions to the slope energy and momentum budgets. Cross-shore variations in the potential vorticity gradient cause the jets to drift continuously offshore, suggesting that fronts observed in regions of AABW down-slope flow may in fact be transient features. [ABSTRACT FROM AUTHOR]

The end of the Eocene greenhouse world was the most dramatic phase in the long-term Cenozoic cooling trend. Here we use 75,000 km of multi/single channel seismic reflection data from offshore Prydz Bay, Antarctica, to provide new insight on the Paleogene stratigraphic transition from greenhouse to icehouse conditions and reorganizing the ocean circulation changes that were invigorated by the cooling and glaciation. We identify a new prominent Paleogene transitional phase (Greenhouse to Icehouse) preserved in the deep-water sedimentary record by correlating from shelf to the continental slope. The occurrence of mega-Mass Transport Deposits (MTDs) on the slope during an early stage in the transition suggests significant instability and collapse of the upper part of the continental margin. A second stage of the transition is represented by the growth of a well-defined set of continental slope clinoforms. We estimate the formation age of the MTDs and clinoforms to be around Eocene-Oligocene Transition. The formation of the clinoforms in the transitional phase indicates sea level has risen, and large volumes sediment delivered to the margin by marine-terminating glaciers on the shelf. Finally, a subsequent marked migration of the margin depocenter toward the west and northwest, attests the onset of drift sedimentation and full glacial conditions, suggesting a more vigorous ocean circulation as the Earth entered the icehouse conditions after the Eocene-Oligocene boundary. [ABSTRACT FROM AUTHOR]

Hydrographic top-to-bottom CTDs and profiling float profiles were collected during 2003–2020 periods in the south-west Indian Ocean sector of the Antarctic margin. Those calibrated dissolved oxygen, temperature and salinity records were used to document the distribution, pathway and changes of the newly-formed Cape Darnley Bottom Water (CDBW). We found that the newly-formed CDBW, with high fractions (50–90%) in the bottom 300 m, primarily appeared on the continental slope (64.5°-70°E) and the abyssal ocean (57°-64.5°E) in the eastern Cooperation Sea. Those distributions of CDBW fractions suggested a pathway originating from the Cape Darnley Polynya (CDP) and descending down Wild and Daly Canyons, and finally accumulating in the northwest abyssal ocean. The newly-formed CDBW presented decadal changes in potential temperature, salinity, dissolved oxygen, and neutral density between 2003-2006 and 2013–2020. It showed significant cooling (∼0.098 °C/decade), freshening (∼0.013/decade), increasing dissolved oxygen (∼11.8 μmol/kg/decade) rates on the continental slope just off CDP, while warming (0.018–0.038 °C/decade), freshening (0.0044–0.0055/decade), decreasing density (0.009–0.014 kg/m3/decade) and increasing dissolved oxygen (4–12 μmol/kg/decade) in the Daly Canyon. The most likely explanation of those high change rates is the enhanced CDBW formation caused by increased cascading Dense Shelf Water (DSW) plumes in Daly Canyon, and subsequently enhanced entrainment of warmer mid-depth Modified Circumpolar Deep Water (MCDW). In the northwest abyssal plain, the potential temperature and dissolved oxygen show little change while the freshening and more buoyant signals remain considerable, which might be influenced by the changes of AABWs from different sources. Finally, we relate the recent changes of newly-formed CDBW to the Sea Ice Production (SIP) change in the CDP. The SIP in the CDP shows significant increasing trends (0.52 m/decade) during 2002–2020. It increased by 12.5% during this period, which indicates an increased formation of regional DSW driven by the sea-ice formation and associated brine rejection, thus increasing formation of CDBW. Those processes were likely responsible for the decadal changes of the recently-formed CDBW. [ABSTRACT FROM AUTHOR]

Continental transform margins are characterized by sub-vertical strike-slip faults and rapid change in thermal gradient across the margin from continental to oceanic crust. The continental crust terminates abruptly along such sheared margins. Tectonic evolution associated with sedimentation in continental slope of the Palar–Pennar transform margin is inadequately understood due to limited seismic data and/or poor imaging with few well controls. Exploratory drilling attempts for hydrocarbon presence have resulted in some promising outcomes in the Palar–Pennar basin. The Palar–Pennar graben in onland is bound by steep normal rift faults, which reactivated by strike-slip movement during late syn-rift time as Antarctica separated along the NNW to ∼ N-trending Coromandal transform margin in the offshore part. The pre-existing Precambrian shear zones and lineaments in the basement have played a governing role in the basin development. The onland drainage pattern is structurally controlled as observed from its rectangular drainage pattern, tectonic index and sinuosity index. In offshore area of the basin, seismic interpretation identifies distinct pull-apart rift basin along the Coromandal transform margin with syn-rift deposits in the lower continental slope portion. Strike-slip movement uplifted the fault blocks in the southern part of the pull-apart basin. This has also reactivated some of the rift faults in the syn-rift section. Such reactivation results in early post-rift seal breach. This tectonic event has implication in the depositional sequences, which has been portrayed by seismic stratigraphic analysis and construction of chronostratigraphic section across the transform margin in this work. Thickening of post-rift deposition towards E -SE, major hiatus, large scale mass transport complexes and erosional events have been identified from such analysis. On this basis, seven distinct tectonic sequences, M1 to M5 in Mesozoic and T1 and T2 in Tertiary, have been identified. The chronostratigraphic section can help in deciphering the relative sea level changes based on the nature of stratal terminations, extent of erosion and non-deposition. This study emphasizes the tectonic-controlled drainage system and geometry as well as sedimentation pattern in onland and offshore deepwater area of Palar – Pennar basin alongside the Coromondal transform margin. • Tectonics of Palar basin interpreted from seismic and geomorphologic perspectives. • The work sheds light on Indian plate's rifting and drifting. • The work has far-reching implication in th epetroleum geoscience of this terrain. [ABSTRACT FROM AUTHOR]

The article discusses the documentation of the spatial distribution of long-term large-scale trends in temperature, salinity, and core depth over the Antarctic continental shelf and slope. Topics include the role of ice shelf basal melt in Antarctic ice sheet mass loss, circulation of Circumpolar Deep Water (CDW), hydrographic properties of the Antarctic Continental Shelf Bottom Water (ASBW) temperature, and factors contributing to warming at the seabed in the Bellingshausen and Amundsen seas.

The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions. • A detailed analysis of Pleistocene sediments from IODP Expedition 374 Site U1525 • Three main intervals of deposition between: 2.4 Ma–1.4 Ma, 1.4 Ma–0.8 Ma and < 0.8 Ma • Depositional context for the Hillary Canyon and the Ross Sea trough-mouth fan • Sandy, foraminifera-bearing interval at ~1.18 Ma suggests ice sheet collapse • Ice grounded at shelf edge more often after 1 Ma, TMF prograded over Site U1525 [ABSTRACT FROM AUTHOR]

Multibeam bathymetric imagery and acoustic sub-bottom profiles are used to reveal distribution patterns of sub-surface sedimentation in Dove Basin (Scotia Sea). The goals of the study are to determine the imprint of the inflow of deep Antarctic water masses from the Weddell Sea into the Scotia Sea, to establish the factors driving the styles of contourite deposition and to discern the relative contribution of alongslope versus downslope processes to the construction of the uppermost late Quaternary sedimentary record in the basin. The most significant morpho-sedimentary features in Dove Basin are linked to contouritic processes and to mass movements. Plastered drifts on the flanks of the basin constitute the most common contouritic deposits. Basement-controlled drifts on top of structural elevations are common along the central ridge, the central basin plain and scattered along the basin flanks. Sheeted drifts occur on top of adjacent banks or are restricted to the deep basin. In contrast, mounded drifts are poorly represented in Dove basin. A laterally extensive contouritic channel runs along the central ridge. Contouritic channels are also identified in the upper parts of the lateral banks and slopes. Numerous slide scars along the upper parts of the slopes evolve downslope into semitransparent lens-shaped bodies, with occasional development of across-slope channels. Semitransparent lenses occur intercalated within stratified deposits in the slopes of the basin, in the central ridge and in the deepest basin plain. The spatial arrangement of contouritic morphologies points to the influence of the water column structure and the basin physiography. In the eastern sub-basin, two different fractions (lower and upper) of Weddell Sea Deep Water (WSDW) leave an imprint on contourite deposits owing to the sloping interface between the two fractions. Contouritic influence is more subdued in the western sub-basin, and limited to the imprint of the lower WSDW. The upper parts of the surrounding banks are under the influence of deep-reaching Circumpolar waters (i.e., Lower Circumpolar Deep Water), which develops both depositional and erosional morphologies. The cross-section V-shaped morphology of the basin and the common occurrence of structural highs drive the predominance of plastered and basement-controlled drifts in the sediment record. The frequent alternation between contourites and downslope gravity-flow deposits is likely due to different processes associated with over-steepening in the basin, such as basement-controlled steep slopes, deformed drifts atop basement elevations, and the development of thick contouritic piles. Dove Basin is an example of a basin without mounded, plastered or mixed hybrid drifts in the transition between the lower slope and the deep basin, because the upper boundary of the deepest water mass —the Weddell Sea Deep Water— flows shallower along the middle slope. This fact underlines the relevance of the position and depth of water masses in shaping the morphology of the feet of slopes along continental margins. • Late Quaternary contourite deposits in Dove Basin show asymmetric distribution. • Sloping interfases and structure of water masses determine the dominant contouritic drifts. • Influence of basin physiography resulted in widespread plastered and tectonically-driven drifts. • Interactions between contouritic processes and mass movements driven by oversteepening and seismic activity. [ABSTRACT FROM AUTHOR]

In the summer seasons of 2004-2007, the intensive runoff (cascading) of the Antarctic shelf water (ASW) down the shelf and continental slope was revealed thanks to the recording of numerous thermohaline profiles across the shelf and continental slope of the Commonwealth Sea and Prydz Bay. The quickly executed profiles (4-10 h) with submesoscale resolution (near the shelf's edge, the scale was even eddy-determinative, i.e., within 1.9-5.6 km), in combination with the fine-structure sounding and fine vertical resolution of the near-bottom boundary layer, provided a qualitatively new level of understanding the natural data. The detailed analysis of the temperature, salinity, and density patterns revealed the regularities and peculiarities of the ASW shelf and slope cascading. The intensive ASW cascading near the shelf break and lower part of the slope can be forced (appearing as discrete frontal meanders) or free (appearing as discrete plumes) and often has a wave-eddy character. The field observational data confirmed the obtained representative estimates of the elements of the ASW slope cascading. The basic area of the ASW formation is near the Amery Shelf Ice, from where the ASW spreads to the northwest, goes around the Fram Bank, and flows down the continental slope. The evaluative contribution of the ASW slope cascading to the ventilation of the deep and slope water of the Southern Ocean (near the shelf break 70 km long where the ASW cascading was observed) is Q = 0.04-0.24 Sv, which agrees well with the analogous estimates obtained in other regions of the Antarctic. [ABSTRACT FROM AUTHOR]

Abstract: The Antarctic continental slope spans the depths from the shelf break (usually between 500 and 1000m) to ∼3000m, is very steep, overlain by ‘warm’ (2–2.5°C) Circumpolar Deep Water (CDW), and life there is poorly studied. This study investigates whether life on Antarctica’s continental slope is essentially an extension of the shelf or the abyssal fauna, a transition zone between these or clearly distinct in its own right. Using data from several cruises to the Weddell Sea and Scotia Sea, including the ANDEEP (ANtarctic benthic DEEP-sea biodiversity, colonisation history and recent community patterns) I–III, BIOPEARL (BIOdiversity, Phylogeny, Evolution and Adaptive Radiation of Life in Antarctica) 1 and EASIZ (Ecology of the Antarctic Sea Ice Zone) II cruises as well as current databases (SOMBASE, SCAR-MarBIN), four different taxa were selected (i.e. cheilostome bryozoans, isopod and ostracod crustaceans and echinoid echinoderms) and two areas, the Weddell Sea and the Scotia Sea, to examine faunal composition, richness and affinities. The answer has important ramifications to the link between physical oceanography and ecology, and the potential of the slope to act as a refuge and resupply zone to the shelf during glaciations. Benthic samples were collected using Agassiz trawl, epibenthic sledge and Rauschert sled. By bathymetric definition, these data suggest that despite eurybathy in some of the groups examined and apparent similarity of physical conditions in the Antarctic, the shelf, slope and abyssal faunas were clearly separated in the Weddell Sea. However, no such separation of faunas was apparent in the Scotia Sea (except in echinoids). Using a geomorphological definition of the slope, shelf-slope-abyss similarity only changed significantly in the bryozoans. Our results did not support the presence of a homogenous and unique Antarctic slope fauna despite a high number of species being restricted to the slope. However, it remains the case that there may be a unique Antarctic slope fauna, but the paucity of our samples could not demonstrate this in the Scotia Sea. It is very likely that various ecological and evolutionary factors (such as topography, water-mass and sediment characteristics, input of particulate organic carbon (POC) and glaciological history) drive slope distinctness. Isopods showed greatest species richness at slope depths, whereas bryozoans and ostracods were more speciose at shelf depths; however, significance varied across Weddell Sea and Scotia Sea and depending on bathymetric vs. geomorphological definitions. Whilst the slope may harbour some source populations for localised shelf recolonisation, the absence of many shelf species, genera and even families (in a poorly dispersing taxon) from the continental slope indicate that it was not a universal refuge for Antarctic shelf fauna. [Copyright &y& Elsevier]

Abstract: The Antarctic Slope Front is an oceanic front that appears to be a semi-permanent feature situated above or near long sections of the shelf break of the Antarctic continental shelf. These sections include the shelf break of the Ross and Weddell Seas. It is distinguished by a V-shaped structure, unique to coastal Antarctica, in which isopycnals slope downward from near the surface on both the shallow (continental shelf) and the deep (continental slope) sides, toward the bottom near the upper part of the slope. In the regions where it is observed, the overflow of dense water from the shelf down the slope is observed or presumed to occur. Such overflows entrain fluid from the overlying stratified environment into the downflow, and this entrainment acts as a distributed sink of the overlying fluid. A model of this frontal structure is constructed here, consisting of the downslope flow modelled as a plume, and the overlying fluid governed by quasi-geostrophic dynamics, with the effect of the plume on the latter being represented by a suitable distribution of sinks. The alongslope currents follow from geostrophy and potential vorticity conservation. Two distinct flow regimes are found. In the first regime, a realistic depiction of the two-sided V-shaped structure is obtained, where most of the fluid flowing off the shelf enters the downflow at the top of the slope constituting the shallow side of the V, and fluid from offshore enters the deep side of the V. Alongslope flow in this region is mostly eastward. In the second regime, where most of the fluid flowing off the shelf passes over the downflow, only the shallow side of the V is present, and alongslope flow is westward near the shelf break and eastward further offshore. [Copyright &y& Elsevier]

Abstract: Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ∼100 to ∼400m on proceeding downslope from ∼600m (the shelf break) to 1200m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ∼35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (<−1°C), salty (>34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (−1.9°C; 34.79) and approaching 1.5ms−1 at descent angles as large as ∼60° relative to the isobaths. Such events were most common during November–May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real, may reflect the influence of the large iceberg C-19 over Drygalski Trough until its departure in mid-May 2003, when there was a marked decrease in the coldest, saltiest gravity current adjacent to Drygalski Trough. Northward transport of cold, saline, recently ventilated Antarctic Bottom Water observed in March 2004 off Cape Adare was ∼1.7Sv, including ∼0.4Sv of High Salinity Shelf Water. [Copyright &y& Elsevier]

Abstract: We use hydrographic, current, and microstructure measurements, and tide-forced ocean models, to estimate benthic and interfacial mixing impacting the evolution of a bottom-trapped outflow of dense shelf water from the Drygalski Trough in the northwestern Ross Sea. During summer 2003 an energetic outflow was observed from the outer shelf (∼500 m isobath) to the ∼1600 m isobath on the continental slope. Outflow thickness was as great as ∼200 m, and mean speeds were ∼0.6 m s−1 relative to background currents exceeding ∼1 m s−1 that were primarily tidal in origin. No outflow was detected on the slope in winter 2004, although a thin layer of dense shelf water was present on the outer shelf. When the outflow was well-developed, the estimated benthic stress was of order one Pascal and the bulk Froude number over the upper slope exceeded one. Diapycnal scalar diffusivity (K z ) values in the transition region at the top of the outflow, estimated from Thorpe-scale analysis of potential density and measurements of microscale temperature gradient from sensors attached to the CTD rosette, were of order 10−3−10−2 m2 s−1. For two cases where the upper outflow boundary was particularly sharply defined, entrainment rate w e was estimated from K z and bulk outflow parameters to be ∼10−3 m s−1 (∼100 m day−1). A tide-forced, three-dimensional primitive equation ocean model with Mellor-Yamada level 2.5 turbulence closure scheme for diapycnal mixing yields results consistent with a significant tidal role in mixing associated with benthic stress and shear within the stratified ocean interior. [Copyright &y& Elsevier]

An array of 40 surface drifters, drogued at 15-m depth, was deployed in February 2007 to the east of the tip of the Antarctic Peninsula as part of the Antarctic Drifter Experiment: Links to Isobaths and Ecosystems (ADELIE) project. Data obtained from these drifters and from a select number of local historical drifters provide the most detailed observations to date of the surface circulation in the northwestern Weddell Sea. The Antarctic Slope Front (ASF), characterized by a ∼20 cm s-1 current following the 1000-m isobath, is the dominant feature east of the peninsula. The slope front bifurcates when it encounters the South Scotia Ridge with the drifters following one of three paths. Drifters (i) are carried westward into Bransfield Strait; (ii) follow the 1000-m isobath to the east along the southern edge of the South Scotia Ridge; or (iii) become entrained in a large-standing eddy over the South Scotia Ridge. Drifters are strongly steered by contours of f /h (Coriolis frequency/depth) as shown by calculations of the first two moments of displacement in both geographic coordinates and coordinates locally aligned with contours of f /h. An eddy-mean decomposition of the drifter velocities indicates that shear in the mean flow makes the dominant contribution to dispersion in the along-f /h direction, but eddy processes are more important in dispersing particles across contours of f /h. The results of the ADELIE study suggest that the circulation near the tip of the Antarctic Peninsula may influence ecosystem dynamics in the Southern Ocean through Antarctic krill transport and the export of nutrients. [ABSTRACT FROM AUTHOR]

The formation of Dense Shelf Water (DSW) and Antarctic Bottom Water (AABW) in the Southern Ocean is an essential part of the thermohaline circulation, and understanding this phenomenon is crucial for studying the global climate. AABW is formed as DSW flows down the continental slope and mixes with the surrounding waters. However, DSW formation and its descent remains a poorly resolved issue in many ocean models. We, therefore, simulated the formation and descent of DSW and investigated the model sensitivities to horizontal and vertical grid spacings. The Massachusetts Institute of Technology general circulation model (MITgcm) was used for the region off Cape Darnley in East Antarctica, one of the main AABW production areas, where historical and mooring data are available for comparison. Simulations with coarse horizontal grid resolutions of order (10 km) yielded high volumes of DSW on the shelf. However, the largest part of this DSW was transformed into intermediate water and advected westward. Horizontal model resolutions equal to or higher than 2 km were required to simulate the descent of DSW and a realistic AABW production. Simulated time series at a mooring located at a depth of 2,600 m showed periodic fluctuations in velocity and temperature of 0.3 m ⋅ s−1 and 0.5 °C, respectively, consistent with observations. We also found that high-resolution bathymetry datasets are crucial because the newly formed AABW volume was reduced by 20% when a smoother bathymetry was used on a 2-km resolution grid. Vertical resolution had little influence on model performance because the plume was much thicker (> 170 m) than the grids width. Therefore, reproducing the downslope flow of DSW and AABW formation in the Cape Darnley region can be achieved with a high horizontal resolution (≤ 2 km) and a relatively coarse vertical resolution (∼ 100 m on the continental slope). • We model AABW formation off Cape Darnley and test its sensitivity to grid spacings. • We simulate AABW formation in good agreement with observations in the region. • Fine horizontal resolutions ≥ 2 km yield realistic downslope flow, AABW properties. • Vertical resolution did not affect the simulation of AABW formation in the region. • Bathymetric data of O (100 km) is required to produce realistic amounts of AABW. [ABSTRACT FROM AUTHOR]

Increased ocean heat supply to the Antarctic continental shelves is projected to cause accelerated ice sheet loss and contribute significantly to global sea-level rise over coming decades. Changes in temperature or salinity of dense shelf waters around Antarctica, resulting from increased glacial meltwater input, have the potential to significantly impact the location and structure of the global Meridional Overturning Circulation, with seabed irregularities such as submarine canyons, driving these flows toward the abyss. Submarine canyons also influence the location of intruding warm water currents by acting as preferential routes for rising Circumpolar Deep Water. These global changes have implications for large-scale effects to atmospheric and oceanic circulation. The ability for numerical modellers to predict these future behaviours is dependent upon our ability to understand both modern and past oceanic, sedimentological and glaciological processes. This knowledge allows ocean models to better predict the flux and pathways of Circumpolar Deep Water delivery to the shelf, and consequently to ice shelf cavities where melt is concentrated. Here we seek to understand how dense shelf water and other continental slope processes influence submarine canyon morphology by analysing newly collected geophysical and oceanographic data from a region of significant and prolonged dense shelf water export, the Hillary Canyon in the Ross Sea. We find that cascading flows of dense shelf water do not contribute to significant gully incision at the shelf edge during interglacial periods, however, are strong enough to prevent gully infilling and contribute to canyon-levee aggradation down-slope. We find buried paleo-gullies beneath gullies incising the modern seafloor. Paleo-gullies occur as single gullies and in complexes indicating that gully activity was continuous over multiple glacial cycles and formed an important role in the development of the shelf edge and upper slope. Glacial cycles likely drive large-scale shifts in canyon head processes with periods of intense seafloor erosion and significant gully incision likely occurring when ice grounded near to the shelf edge, during glacial and deglacial periods, when sediment-laden subglacial meltwater was released at the shelf edge. We put slope morphology observed at the Hillary Canyon head into global perspective to show that cascading flows of dense shelf water do not exert consistent patterns of erosion on high-latitude continental margins. Unlabelled Image • New geophysical, sediment and oceanographic data show Antarctic canyon dynamics. • Irregular gully distribution along shelf edge show varying ice extent. • Dense shelf water does not cause significant gully erosion. • Glacial cycles drive large-scale shifts in canyon head processes. [ABSTRACT FROM AUTHOR]

The Prydz Bay region of Antarctica is the immediate recipient of ice and sediments transported by the Lambert Glacier, the single largest outflow from the East Antarctic Ice Sheet. The continental slope and rise provide records covering multiple glacial cycles and containing paleoclimatic information. Marine geological and geophysical data collected from the continental shelf and adjacent slope of Prydz Bay, Antarctica, including seismic reflection data, bathymetry, and core records from ODP drilling sites, reveal the history of glacial sediment transport and deposition since the early Pliocene times. Seismic facies are interpreted in terms of episodes of slope progradation, contourite, turbidite, trough-mouth fan, and mass transport deposition. Two seismic units with estimated age of early to late Pliocene and late Pliocene to recent have been analyzed in detail for the area immediately offshore the Lambert Glacier and Prydz Bay and the adjacent Mac. Robertson margin. The upper slope is dominated by episodic mass transport deposits, many of which accumulated to form a trough mouth fan since Early Pliocene times. The trough mouth fan contrasts with the adjacent steep (4–6°) continental slope of the Mac. Robertson margin, where glacigenic sediments have been transported down slope as high-velocity turbidity currents via submarine channels. The distal region exhibits evidence for contrasting effects of high-energy, traction-dominated versus lower-energy, fallout-dominated suspension flows. The counter-clockwise Coriolis force modifies the erosion and deposition patterns of turbidity currents creating an asymmetric channel-levee architecture. Since the early Pliocene, turbidite sedimentation surpassed the amount of sediment reworked and transported by westward-flowing contour currents along the base of slope. On the continental rise, contourites and sediment waves were deposited in response to enhanced bottom-water formation, which is consistent with climatic cooling since late Pliocene times. This study, based on existing seismic reflection and ODP data, highlights the need for a future scientific ocean drilling proposal on the Prydz Bay continental slope and rise in order to more accurately determine the timing of the important events that have influenced the evolution of this margin. • The geomorphologic setting of Prydz Bay and its marginal architecture of the Pliocene and their linkage to the paleoclimate change. • The role of Wild Canyon on the Mac. Robertson Land margin and its associated depositional and erosional features. • The observation of drift deposits and long-lived sediment waves indicate a vigorous ocean circulation in the late Pliocene. [ABSTRACT FROM AUTHOR]

The Antarctic continental margin supplies the densest bottom water to the global abyss. From the late twentieth century, an acceleration in the long-term freshening of Antarctic Bottom Waters (AABW) has been detected in the Australian-Antarctic Basin. Our latest hydrographic observations reveal that, in the late 2010s, the freshening trend has reversed broadly over the continental slope. Near-bottom salinities in 2018–2019 were higher than during 2011–2015. Along 170° E, the salinity increase between 2011 and 2018 was greater than that observed in the west. The layer thickness of the densest AABW increased during the 2010s, suggesting that the Ross Sea Bottom Water intensification was a major source of the salinity increase. Freshwater content on the continental slope decreased at a rate of 58 ± 37 Gt/a in the near-bottom layer. The decadal change is very likely due to changes in Ross Sea shelf water attributable to a decrease in meltwater from West Antarctic ice shelves for the corresponding period. [ABSTRACT FROM AUTHOR]

The continental slope and rise seaward of the Totten Glacier and the Sabrina Coast, East Antarctica features continental margin depositional systems with high sediment input and consistent along-slope current activity. Understanding their genesis is a necessary step in interpreting the paleoenvironmental records they contain. Geomorphic mapping using a systematic multibeam survey shows variations in the roles of downslope and along slope sediment transport influenced by broad-scale topography and oceanography. The study area contains two areas with distinct geomorphology. Canyons in the eastern part of the area have concave thalwegs, are linked to the shelf edge and upper slope and show signs of erosion and deposition along their beds suggesting cycles of activity controlled by climate cycles. Ridges between these canyons are asymmetric with crests close to the west bank of adjacent canyons and are mostly formed by westward advection of fine sediment lofted from turbidity currents and deposition of hemipelagic sediment. They can be thought of as giant levee deposits. The ridges in the western part of the area have more gently sloping eastern flanks and rise to shallower depths than those in the east. The major canyon in the western part of the area is unusual in having a convex thalweg; it is likely fed predominantly by mass movement from the flanks of the adjacent ridges with less sediment input from the shelf edge. The western ridges formed by accretion of suspended sediment moving along the margin as a broad plume in response to local oceanography supplemented with detritus originating from the Totten Glacier. This contrasts with interpretations of similar ridges described from other parts of Antarctica which emphasise sediment input from canyons immediately up-current. The overall geomorphology of the Sabrina Coast slope is part of a continuum of mixed contourite-turbidite systems identified on glaciated margins. • The slope and rise off the Totten Glacier feature sediment ridges between submarine canyons. • Sediment ridges in the east are formed from turbidity currents flowing in adjacent canyons and a pelagic component. • In the west, larger ridges are formed from widespread hemipelagic and contouritic sedimentation. • The western ridges are separated by a submarine canyon with a convex thalweg mostly sourced from the ridge flanks. [ABSTRACT FROM AUTHOR]

The article reports on the studies conducted during the 55th Russian Antarctic Expedition between December 9, 2009 and February 16, 2010. It says that the study, done on board the research vessel Akademik Fedorov, analyzed the hydrochemical and hydrological structure of the Southern Ocean and its water circulation. It explains why the main interest of the study, the shelf and continental slope of the West Antarctic Peninsula, plays an important role in the Southern Ocean and around the world.

This study applies detailed seafloor bathymetry data and seafloor images to understand upper slope features and how these influence the distribution of seafloor biota on the East Antarctic margin. The East Antarctic slope on the Sabrina margin has been shaped by diverse processes related to repeated glaciation. Differences in the morphology of gullies on the upper slope enable an understanding of the likely processes that have been active on this margin. Gully morphology varies according to changes in slope gradient, which may have driven variations in sedimentation. Areas of lower slope angles may have led to rapid sediment deposition during glacial expansion to the shelf edge, and subsequent sediment failure. Typically, gullies in these areas are U-shaped, initiate well below the shelf break, are relatively straight and long, and have low incision depths, consistent with formation due to mass wastage. Areas of higher slope angles likely experienced enhanced flow of erosive turbidity currents during glaciations associated with the release of sediment-laden basal meltwaters. Sediment-laden subglacial meltwater flows typically create gullies such as those we observe that initiate at, or near, the shelf break; are V-shaped in profile; and have high sinuosity, deep incision depths and a relatively short downslope extent. The short downslope extent reflects a reduced sediment load associated with increased seawater entrainment as the slope becomes more concave in profile. These differences in gully morphology have important habitat implications associated with differences in the composition and beta-diversity of the seafloor communities. This upper slope region also supports seafloor communities that are distinct from those on the adjacent shelf, highlighting the uniqueness of this environment for biodiversity. Conservation strategies therefore need to consider slope and shelf communities as distinct and equally important components of the Antarctic ecosystem. • Upper slope gullies on this Antarctic margin have distinct morphology. • Upper slope morphology is driven largely by variations in depositional history. • Benthic community structure and beta-diversity is associated with gully morphology. • Upper slope communities are distinct from the adjacent continental shelf. [ABSTRACT FROM AUTHOR]

Paleo ice sheet reconstruction in Antarctica provides key constrains for understanding and predicting future ice sheet behaviour. Along the East Antarctic margin there are still large sections with little or no information about previous extent and dynamics of the paleo-ice sheet. Here we present new multibeam and Chirp subbottom data from the East Antarctic continental margin between the Frost and Dibble Glaciers (128°E and 134°E), acquired during expedition NBP1503 with the icebreaker NB Palmer. The inner continental shelf shows a moderately deep seafloor (200–600 m) with steep and deeply incised channels, most likely created by subglacial meltwater. On the mid shelf we identified a ~1000 m deep basin with drumlin-shaped and linear glacial features. The shelf break is relatively shallow (300–400 m) and incised by numerous gullies that extent onto the continental slope. The presence of these features suggests that grounded, streaming ice has reached the shelf break during the last glaciation. Both, the subglacial channels on the continental shelf and the numerous gullies near the shelf break are indicative of melt water underneath the grounding ice. Our interpretation suggests that compared to toady the ice flow in this area might have been significantly different during glacial times when the paleo ice sheet cover most or all of the continental shelf. • New bathymetry and subbottom data from the continental margin near the Dibble Glacier reveal paleo ice flow pattern of the former ice sheet in this area • Streaming, grounded ice of the Dibble glacier extended to the continental shelf break during a recent, probably the last glacial maximum • Indication for presence of subglacial melt water and sediment transport be the streaming ice [ABSTRACT FROM AUTHOR]

The systematic survey of Antarctic margin sedimentary sequences offers, especially in poorly investigated areas, the opportunity to obtain a wide range of information on glacio-eustatic, climatic, and tectonic events. Multidisciplinary datasets resulting from geophysical surveys and scientific coring and drilling are needed to address questions regarding the orbital forcing and the global response of the hydrosphere (oceans and atmosphere), cryosphere, and biosphere. The PNRA Tytan Project, embedded into the Australian project "Interactions of the Totten Glacier with the Southern Ocean through multiple glacial cycles" (Australian National University), aims to understand how the Totten Glacier behaved during past Holocene and Pleistocene times of warmer climate. Insights for reconstructing the depositional and hydrodynamic environments of the continental margin off the Totten Glacier, a large outlet glacier located on the Sabrina Coast of East Antarctica, are addressed through micropaleontological efforts. The micropaleontological research group focused on identification of diatom biostratigraphic markers and assemblage analyses in sediment cores collected from the Sabrina Coast continental slope during the RV Investigator mission IN2017_V01 in order to reconstruct paleoenvironments and to place age constraints on the sedimentary sequences.All but one of the piston cores recovered late Pleistocene sediments, documenting MIS 9 – MIS 1, with interglacial intervals characterized by diatomaceous sediments dominated by the open water taxon Fragilariopsis kerguelensis. Glacial intervals have much lower diatom concentrations and a higher proportion of reworked forms. A single piston core, IN2017_V01_PC03, recovered a more complicated sedimentary sequence. This sequence, targeted for an older and more condensed coring location, was selected for coring based on the sub-bottom geophysical data that indicated thinning of the upper stratigraphic section, and greater access to the underlying section. The results suggest a very dynamic sediment delivery system in a context of Pliocene–Recent Antarctic continental margin. The basal section of the core is marked by Eocene-Oligocene reworked taxa while the mid section is characterized by almost barren sediments. The silty top section of the PC03 core, had diatom assemblages similar to the other kasten and piston cores; t his sectionis characterized by modern diatom assemblages dominated by Circum Antarctic Current and open water taxa with a variable presence of sea ice associated forms. Glacial slumping, perhaps facilitated by the presence of biogenic silica, and reworking may have removed or prevented deposition within this condensed sedimentary sequence. The presence or absence of F. kerguelensis versus F. barronii and also the presence of transitional forms between these two species, confirms the much older nature of the sediments in this core as compared to the other piston cores. In addition, Denticulopsis simonsenii much more common at the basal part of the core, may reflect erosional contributions from Miocene-aged sediment, while the significant contribution of F. barronii, Thalassiosira lentiginosa and Thalassiosira oliverana (var. sparsa?) versus intervals dominated by D. simonsenii may suggest different sources of material. [ABSTRACT FROM AUTHOR]