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Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice‐sheet dynamics. Yet, direct data are sparse and difficult to acquire. Here, we employ ultra‐wideband radar to map high‐backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. Our backscatter analysis reveals that the basal ice in an area of ∼10,000 km2 is composed of along‐flow oriented sediment‐laden basal ice units connected to the basal substrate, extending up to several hundred meters thick. Three‐dimensional thermomechanical modeling supports that these units form via basal freeze‐on of subglacial water that originated from further upstream. Our findings suggest that basal freeze‐on, and the entrainment and transport of subglacial material play a significant role in an accurate representation of material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice‐sheet modeling. Plain Language Summary: We investigate the lowermost portion of the ice column of the Antarctic ice sheet, known as basal ice. This part holds crucial information about how the ice sheet behaves when it flows. Using the principle of echo‐location, we use radar technology to scan the ice in East Antarctica's Jutulstraumen drainage basin. We discover that a significant portion of the basal ice in this region is filled with sediment and can be several hundred meters thick. To better understand how this distinctive type of ice forms, we used a mathematical model that suggested that these ice units likely form when water underneath the ice is transported and refreezes at particular locations. Our findings highlight the importance of these freezing and mixing of materials from beneath the ice. Understanding where these ice units are located provides important information for ice‐flow models to ultimately better understand how the Antarctic ice sheet behaves in the future. Key Points: We have identified high‐scattering basal ice in Jutulstraumen Glacier's onset region using radar, reaching several hundred meters from the bedBackscatter analysis suggests that the basal ice units contain unstratified point scatters and cause little radio‐glaciological loss3D thermo‐mechanical modeling implies that freeze‐on of basal meltwater generated upstream likely initially formed the basal ice units [ABSTRACT FROM AUTHOR]

The ocean is the main heat reservoir in Earth's climate system, absorbing most of the top-of-the-atmosphere excess radiation. As the climate warms, anomalously warm and fresh ocean waters in the densest layers formed near Antarctica spread northward through the abyssal ocean, while successions of warming and cooling events are seen in the deep-ocean layers formed near Greenland. The abyssal warming and freshening expands the ocean volume and raises sea level. While temperature and salinity characteristics and large-scale circulation of upper 2000 m ocean waters are well monitored, the present ocean observing network is limited by sparse sampling of the deep ocean below 2000 m. Recently developed autonomous robotic platforms, Deep Argo floats, collect profiles from the surface to the seafloor. These instruments supplement satellite, Core Argo float, and ship-based observations to measure heat and freshwater content in the full ocean volume and close the sea level budget. Here, the value of Deep Argo and planned strategy to implement the global array are described. Additional objectives of Deep Argo may include dissolved oxygen measurements, and testing of ocean mixing and optical scattering sensors. The development of an emerging ocean bathymetry dataset using Deep Argo measurements is also described. [ABSTRACT FROM AUTHOR]

Realistic characterization of subglacial hydrology necessitates knowledge of the range in form, scale, and spatiotemporal evolution of drainage networks. A relict subglacial meltwater corridor on the deglaciated Antarctic continental shelf encompasses 80 convergent and divergent channels, many of which are hundreds of meters wide and several of which lack a definable headwater source. Without significant surface‐melt contributions to the bed like similarly described landforms in the Northern Hemisphere, channelized drainage capacity varies non‐systematically by three orders of magnitude downstream. This signifies apparent additions and losses of basal water to the bed‐channelized system that relates to bed topography. Larger magnitude grounding‐line retreat events occurred while the channel system was active than once channelized drainage had ceased. Overall, this corridor demonstrates that meltwater drainage styles co‐exist in time and space in response to bed topography, with prolonged impacts on grounding‐line behavior. Plain Language Summary: Water drainage beneath glacial ice can impact flow of the overlying ice, sediment transport underneath the ice toward the glacier's terminus, and the stability of glacial ice as it transitions from resting on the geologic terrain to floating in the ocean. Despite being an important component of glacial systems, the full range of possible modes of water delivery and how these interact and vary across time and space is not well resolved. We describe a relict subglacial meltwater network preserved on the Antarctic seafloor, representing a persistent pathway for water drainage when the East Antarctic Ice Sheet was much larger. The landforms within the drainage network implicate substantial changes in how subglacial water drainage was influenced by the shape of the underlying terrain and demonstrate the prolonged impacts that meltwater corridors have on the retreat of glacial ice. Key Points: Bed topography was the primary control on the morphology and organization of a large paleo‐subglacial meltwater corridor in AntarcticaThe morphology of the corridor supports downstream gains and losses in meltwater supply and/or changes in drainage styleGrounding‐line retreat events were significantly larger when channels were active and smaller when channelized drainage had ceased [ABSTRACT FROM AUTHOR]

The Labyrinth in the McMurdo Dry Valleys of Antarctica is characterized by large bedrock channels emerging from beneath the margin of Wright Upper Glacier. To study the morphodynamics of large subglacial channels cut into bedrock, we develop herein a numerical model based on the classical theory of subglacial channels and recent results on bedrock abrasion by saltating bed load. Model results show that bedrock abrasion in subglacial channels with pressurized flow reaches a maximum at an intermediate distance up-ice from the glacier snout for a wide range of sediment grain sizes and sediment loads. Close to the snout, the velocity is too low and the sediment particles cannot be mobilized. Far from the snout, the flow accelerates and sediment is transported in suspension, thus limiting particle impacts at the channel bottom and reducing abrasion. This non-monotonic relationship between subglacial flow and bedrock abrasion produces concave up bottom profiles in subglacial channels and potential cross-section constrictions after channel confluences. Both landforms are present in the bedrock channels of the Labyrinth. We therefore conclude that these geomorphic features are a possible signature of bedrock abrasion, rather than glacial scour, and reflect the complex interplay between transport rate, sediment load, and transport capacity in subglacial channels. [ABSTRACT FROM AUTHOR]

On high‐latitude continental margins sediment is supplied from land to the deep sea through a variety of processes, including iceberg and sea‐ice rafting, and bottom current transport. The accurate reconstruction of sediment fluxes from these sources through time is important in palaeoclimate reconstructions. The goal of this study was to assess a shift in the intensity of glacial processes, iceberg and sea‐ice rafting during the Pliocene through an investigation of coarse sediment deposited at the AND‐2A site in the Ross Sea and at International Ocean Discovery Program Site U1359 on the Antarctic continental rise. Terrigenous particle‐size distributions and suites of quartz grain microtextures in the sand fraction of the deep‐sea sediments were compared to those from Antarctic glaciomarine diamictites as a baseline for proximal glacial sediment in its source area. Using images acquired through Scanning Electron Microscopy, and following a quantitative approach, fewer immature and potentially glacially transported grains were found in Pliocene deep‐sea sand fractions than in ice‐contact sediments. Specifically, in the lower Pliocene interval silt and fine sand percentages are elevated, and microtextures in at least half of the sand fraction are inconsistent with a primary glacial origin. Larger numbers of chemically altered and abraded grains in the deep‐sea sand fraction, along with microtextures that are diagnostic of periglacial environments, suggest a role for eolian sediment transport. These results highlight the anomalous nature of high‐latitude sediment fluxes during prolonged periods of ice retreat. Furthermore, the identification of a significant offshore sediment flux during Antarctic deglaciation has implications for estimated nutrient supply to the Southern Ocean and the potential for high‐latitude climate feedbacks under warmer climate states. [ABSTRACT FROM AUTHOR]

In this study, we interpret the role played by ocean circulation in sediment distribution on the southwestern Atlantic margin using radiogenic Nd and Pb isotopes. The latitudinal trends for Pb and Nd isotopes reflect the different current systems acting on the margin. The utilization of the sediment fingerprinting method allowed us to associate the isotopic signatures with the main oceanographic features in the area. We recognized differences between Nd and Pb sources to the Argentinean shelf (carried by the flow of Subantarctic Shelf Water) and slopes (transported by deeper flows). Sediments from Antarctica extend up to the Uruguayan margin, carried by the Upper and Lower Circumpolar Deep Water. Our data confirm that, for shelf and intermediate areas (the upper 1200 m), the transfer of sediments from the Argentinean margin to the north of 35 ∘ S is limited by the Subtropical Shelf Front and the basin-wide recirculated Antarctic Intermediate Water. On the southern Brazilian inner and middle shelf, it is possible to recognize the northward influence of the Río de la Plata sediments carried by the Plata Plume Water. Another flow responsible for sediment transport and deposition on the outer shelf and slope is the southward flow of the Brazil Current. Finally, we propose that the Brazil–Malvinas Confluence and the Santos Bifurcation act as boundaries of geochemical provinces in the area. A conceptual model of sediment sources and transport is provided for the southwestern Atlantic margin. [ABSTRACT FROM AUTHOR]