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Initial staging of code associated with Verboncoeur and others (2024) in Journal of Glaciology. Contact Hannah at hverboncoeur@mines.edu with questions. Data associated with this code can be found on Zenodo here. GitHub: https://github.com/hverboncoeur/Verboncoeur2024-JoG 

Abstract The ongoing deceleration of Whillans Ice Stream, West Antarctica, provides an opportunity to investigate the co-evolution of ice-shelf pinning points and ice-stream flux variability. Here, we construct and analyze a 20-year multi-mission satellite altimetry record of dynamic ice surface-elevation change (dh/dt) in the grounded region encompassing lower Whillans Ice Stream and Crary Ice Rise, a major pinning point of Ross Ice Shelf. We developed a new method for generating multi-mission time series that reduces spatial bias and implemented this method with altimetry data from the Ice, Cloud, and land Elevation Satellite (ICESat; 2003–09), CryoSat-2 (2010–present), and ICESat-2 (2018–present) altimetry missions. We then used thedh/dttime series to identify persistent patterns of surface-elevation change and evaluate regional mass balance. Our results suggest a persistent anomalous reduction in ice thickness and effective backstress in the peninsula connecting Whillans Ice Plain to Crary Ice Rise. The multi-decadal observational record of pinning-point mass redistribution and grounding zone retreat presented in this study highlights the on-going reorganization of the southern Ross Ice Shelf embayment buttressing regime in response to ice-stream deceleration. 

v2.0 of this dataset includes: All surface-elevation change (dh/dt) data from ICESat, CryoSat-2, and ICESat-2 altimetry missions necessary to reproduce figures and analysis from Verboncoeur et al. (2024) ('*dhdt_smb'); a file containing x,y positions of the ad-hoc reference tracks formed around ICESat ground tracks ('xy_is_masked.csv'); a folder containing delineated boundaries used in analysis ('SHAPES.zip'); folders containing raw subsetted ICESat data ('IS_data.zip') and a folder containing CryoCloud scripts for downloading ICESat-2 data ('IS2_processing_cryocloud.zip') 

Abstract Beneath Antarctica’s ice sheets, a little-observed network of liquid water connects vast landscapes and contributes to the motion of the overriding ice. When this subglacial water reaches the ocean cavity beneath ice shelves, it mixes with seawater, amplifying melt and in places forming deep channels in the base of the ice. Here we present observations from a hot-water-drilled borehole documenting subglacial water entering the ocean cavity at the grounding zone of Kamb Ice Stream and the Ross Ice Shelf. Our observations show that melt has removed approximately a third of the ice thickness, yet measurements reveal low rates of subglacial discharge in a turbid plume. Sediment cored from the channel floor shows larger discharge events occur and episodically deposit material from distinct geological domains. We quantify subglacial discharge and link our observations to the catchment upstream. We conclude that discrete discharge events are likely to dominate channel melt and sediment transport and result in the extensive ice-shelf features downstream of Kamb Ice Stream. 

Abstract. Since distributed satellite observations of elevation change and velocity became available in the 1990s, Thwaites, Pine Island, Haynes, Pope, and Kohler Glaciers, located in Antarctica’s Amundsen Sea Embayment, have thinned and accelerated in response to ocean-induced melting and grounding-line retreat. We develop a crevasse image segmentation algorithm to identify and map surface crevasses on the grounded portions of Thwaites, Pine Island, Haynes, Pope, and Kohler Glaciers between 2015 and 2022 using Sentinel-1A satellite synthetic aperture radar (SAR) imagery. We also develop a geometric model for firn tensile strength dependent on porosity and the tensile strength of ice. On Pine Island and Thwaites Glaciers, which have both accelerated since 2015, crevassing has expanded tens of kilometers upstream of the 2015 extent. From the crevasse time series, we find that crevassing is strongly linked to principal surface stresses and consistent with von Mises fracture theory predictions. Our geometric model, analysis of SAR, and optical imagery, together with ice-penetrating radar data, suggest that these crevasses are near-surface features restricted to the firn. The porosity dependence of the near-surface tensile strength of the ice sheet may explain discrepancies between the tensile strength inferred from remotely-sensed surface crevasse observations and tensile strength measured in laboratory experiments, which often focus on ice (rather than firn) fracture. The near-surface nature of these features suggests that the expansion of crevasses inland has a limited direct impact on glacier mechanics. 

Abstract We present Bedmap3, the latest suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60 °S. Bedmap3 incorporates and adds to all post-1950s datasets previously used for Bedmap2, including 84 new aero-geophysical surveys by 15 data providers, an additional 52 million data points and 1.9 million line-kilometres of measurement. These efforts have filled notable gaps including in major mountain ranges and the deep interior of East Antarctica, along West Antarctic coastlines and on the Antarctic Peninsula. Our new Bedmap3/RINGS grounding line similarly consolidates multiple recent mappings into a single, spatially coherent feature. Combined with updated maps of surface topography, ice shelf thickness, rock outcrops and bathymetry, Bedmap3 reveals in much greater detail the subglacial landscape and distribution of Antarctica’s ice, providing new opportunities to interpret continental-scale landscape evolution and to model the past and future evolution of the Antarctic ice sheets. 

Radio-echo sounding (RES) has revealed an internal architecture within both the West and East Antarctic ice sheets that records their depositional, deformational and melting histories. Crucially, RES-imaged internal-reflecting horizons, tied to ice-core age–depth profiles, can be treated as isochrones that record the age–depth structure across the Antarctic ice sheets. These enable the reconstruction of past climate and ice dynamical processes on large scales, which are complementary to but more spatially extensive than commonly used proxy records (e.g. former ice limits constrained by cosmogenic dating or offshore sediment sequences) around Antarctica. We review the progress towards building a pan-Antarctic age–depth model from these data by first introducing the relevant RES datasets that have been acquired across Antarctica over the last 6 decades (focussing specifically on those that detected internal-reflecting horizons) and outlining the processing steps typically undertaken to visualise, trace and date (by intersection with ice cores or modelling) the RES-imaged isochrones. We summarise the scientific applications for which Antarctica's internal architecture has been used to date and present a pathway to expanding Antarctic radiostratigraphy across the continent to provide a benchmark for a wider range of investigations: (1) identification of optimal sites for retrieving new ice-core palaeoclimate records targeting different periods; (2) reconstruction of surface mass balance on millennial or historical timescales; (3) estimation of basal melting and geothermal heat flux from radiostratigraphy and comprehensive mapping of basal-ice units to complement inferences from other geophysical and geological methods; (4) advancement of the knowledge of volcanic activity and fallout across Antarctica; and (5) refinement of numerical models that leverage radiostratigraphy to tune time-varying accumulation, basal melting and ice flow, firstly to reconstruct past behaviour and then to reduce uncertainties in projecting future ice-sheet behaviour. 

Hercules Dome, Antarctica, has long been identified as a prospective deep ice core site due to the undisturbed internal layering, climatic setting and potential to obtain proxy records from the Last Interglacial (LIG) period when the West Antarctic ice sheet may have collapsed. We performed a geophysical survey using multiple ice-penetrating radar systems to identify potential locations for a deep ice core at Hercules Dome. The surface topography, as revealed with recent satellite observations, is more complex than previously recognized. The most prominent dome, which we term ‘West Dome’, is the most promising region for a deep ice core for the following reasons: (1) bed-conformal radar reflections indicate minimal layer disturbance and extend to within tens of meters of the ice bottom; (2) the bed is likely frozen, as evidenced by both the shape of the measured vertical ice velocity profiles beneath the divide and modeled ice temperature using three remotely sensed estimates of geothermal flux and (3) models of layer thinning have 132 ka old ice at 45–90 m above the bed with an annual layer thickness of ~1 mm, satisfying the resolution and preservation needed for detailed analysis of the LIG period. 

Dielectric anisotropy in ice alters the propagation of polarized radio waves, so polarimetric radar sounding can be used to survey anisotropic properties of ice masses. Ice anisotropy is either intrinsic, associated with ice‐crystal orientation fabric (COF), or extrinsic, associated with material heterogeneity, such as bubbles, fractures, and directional roughness at the glacier bed. Anisotropy develops through a history of snow deposition and ice flow, and the consequent mechanical properties of anisotropy then feed back to influence ice flow. Constraints on anisotropy are therefore important for understanding ice dynamics, ice‐sheet history, and future projections of ice flow and associated sea‐level change. Radar techniques, applied using ground‐based, airborne, or spaceborne instruments, can be deployed more quickly and over a larger area than either direct sampling, via ice‐core drilling, or analogous seismic techniques. Here, we review the physical nature of dielectric anisotropy in glacier ice, the general theory for radio‐wave propagation through anisotropic media, polarimetric radar instruments and survey strategies, and the extent of applications in glacier settings. We close by discussing future directions, such as polarimetric interpretations outside COF, planetary and astrophysical applications, innovative survey geometries, and polarimetric profiling. We argue that the recent proliferation in polarimetric subsurface sounding radar marks a critical inflection, since there are now several approaches for data collection and processing. This review aims to guide the expanding polarimetric user base to appropriate techniques so they can address new and existing challenges in glaciology, such as constraining ice viscosity, a critical control on ice flow and future sea‐level change.