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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]

A quantitative understanding of how sediment discharge from subglacial fluvial systems varies in response to glacio-hydrological conditions is essential for understanding marine systems around Greenland and Antarctica and for interpreting sedimentary records of cryosphere evolution. Here we develop a graph based approach, GraphSSeT, to model subglacial fluvial sedimentary transport using subglacial hydrology model outputs as forcing. GraphSSeT includes glacial erosion of bedrock and a dynamic sediment model with exchange between the active transport system and a basal sediment layer. Sediment transport considers transport-limited and supply-limited regimes and includes stochastically-evolving grain size, network scale flow management and tracking of detrital provenance. GraphSSeT satisfies volume balance and sediment velocity and transport capacity constraints on flow. GraphSSeT is demonstrated for synthetic scenarios that probe the impact of variations in hydrological, geological and glaciological characteristics on sediment transport over multi-diurnal to seasonal timeframes. For steady-state hydrology scenarios on seasonal timescales we find a primary control from the scale and organisation of the channelised hydrological flow network. The development of grain size dependant selective transport is identified as the major secondary control. Non-steady-state hydrology is tested on multi-diurnal timescales, for which sediment discharge scales with peak water input leading to increased sediment discharge compared to steady state. With increasing application of subglacial hydrology models, GraphSSeT extends this capacity to define quantitatively the volume, grain size distribution and detrital characteristics of sediment discharge, and enables a stronger connection of models of the glacio-hydrological system with constraints from the sediment record and impacts on marine systems. [ABSTRACT FROM AUTHOR]

To reconstruct the interaction between Antarctic Bottom Water (AABW) and global climate change, extracting information about past AABW formation from the sedimentary record is crucial. The Prydz Bay region, East Antarctica, has high glacier outflow and is a region of vigorous formation of AABW associated with sea ice formation. The Cape Darnley Bottom Water (CDBW), a primary AABW precursor, flows into Wild Canyon west of Prydz Bay. Thus, the sedimentary record of Wild Canyon can serve as an archive for CDBW flow. In this study, to identify the sedimentary processes and mineral compositions characteristic of CDBW flow, we evaluate deep-sea camera imagery, X-ray computed tomography images, grain-size data, and optical and chemical mineralogical analyses. Heavy minerals in the surface sediments are characterized by pyrope-rich almandine garnets (up to 80% of the heavy-mineral assemblage, 0.2%–3.7% of the dry bulk sediment by weight) typical of nearshore sediment derived from Mac. Robertson Land. In addition, ripples on the channel floor indicate sediment transport occurred as tractional bedload, whereas settling of suspended sediment prevailed on the canyon levee. We propose that modern CDBW flow is the dominant process of sediment reworking through sustained high flow velocities, distinctly different from turbidity currents triggered by ice sheet expansion and rapid retreat. Our results further suggest that fine-grained sediments are transported to the canyon levee as CDBW flows through the submarine canyon. These findings will be a key for reconstructing past AABW formation, which is crucial for understanding the response of AABW to future climate change. • Ripples formed by Cape Darnley Bottom Water are identified in Wild Canyon. • Antarctic Bottom Water flow triggers the reworking of pre-existing sediments. • Sedimentary processes are different during AABW active/inactive periods. [ABSTRACT FROM AUTHOR]