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Melting and refreezing processes in the firn of the Devon Ice Cap control meltwater infiltration and runoff across the ice cap, but their full spatial extent and effect on near-surface structure is difficult to measure with surface-based traverses or existing satellite remote sensing. Here, we derive the coherent component of the near-surface return from airborne ice-penetrating radar surveys over the Devon Ice Cap, Canadian Arctic, to characterize firn containing centimeter- to meter-thick ice layers (i.e., ice slabs) formed from refrozen meltwater in firn. We assess the use of dual-frequency airborne ice-penetrating radar to characterize the spatial and vertical near-surface structure of the Devon Ice Cap by leveraging differences in range resolution of the radar systems. Comparison with reflectivities using a thin layer reflectivity model, informed by surface-based radar and firn core measurements, indicates that the coherent component is sensitive to the near-surface firn structure composed of quasi-specular ice and firn layers, limited by the bandwidth-constrained radar range resolution. Our results suggest that average ice slab thickness throughout the Devon Ice Cap percolation zone ranges from 4.2 to 5.6 m. This implies conditions that can enable lateral meltwater runoff and potentially contribute to the total surface runoff routed through supraglacial rivers down glacier. Together with the incoherent component of the surface return previously studied, our dual-frequency approach provides an alternative method for characterizing bulk firn properties, particularly where high-resolution radar data are not available.

Over the past 60 years, scientists have strived to understand the past, present and future of the Antarctic Ice Sheet. One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice-bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future survey and gridded datasets accessible under the ‘Findable, Accessible, Interoperable and Reusable’ (FAIR) data principles. With the goals to make the gridding process reproducible and to allow scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (bedmap.scar.org, last access: 18 October 2022) created to provide unprecedented open access to these important datasets, through a user-friendly webmap interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data held within it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk.

Europa Subsurface Studies: The Europa Clipper is a NASA mission to study Europa, the ice-covered moon of Jupiter characterized by a global sub-ice ocean overlying a silicate mantle, through a series of fly-by observations from a spacecraft in Jovian orbit. The science goal is to “explore Europa to investigate its habitability”. The Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) is one of the primary instruments of the scientific payload. REASON is an active dual-frequency (9/60 MHz) instrument led by the University of Texas Institute for Geophysics (UTIG). It is designed to achieve multi-disciplinary measurements to investigate subsurface waters and the ice shell structure (Sounding), the surface elevation and tides (Altimetry), near-surface physical properties (Reflectometry), and the ionospheric environment including plume activity (Plasma/Particles). REASON will play a critical role in achieving the mission’s habitability driven science objectives, which include characterizing the distribution of any shallow subsurface water, searching for an ice-ocean interface and evaluating a broad spectrum of ice-ocean-atmosphere exchange hypotheses. Terrestrial Analogs: The development of successful measurement approaches and data interpretation techniques for exploring Europa and understanding its habitability will need to leverage knowledge of analogous terrestrial environments and processes. Towards this end, we are investigating, and considering for future investigations, a range of terrestrial radio glaciological analogs for hypothesized physical, chemical, and biological processes on Europa and present airborne data collected with the UTIG/University of Kansas dual-frequency radar system over a variety of terrestrial targets relevant to Europa’s potential exchange processes and habitability. These targets include water filled fractures, brine rich ice, subglacial lakes, accreted marine ice, and ice roughness ranging from porous ice regolith (firn) to extensive crevasse fields. Our goal is to provide context for understanding and optimizing the observable signature of these processes in future radar data collected at Europa with implications for its habitability.

The near-surface (i.e., depths of tens of meters from the surface) of icy environments is subject to various processes resulting in changes to its structure, density, and composition. On Earth, surface meltwater can refreeze in firn to form meters-thick ice layers, which can inhibit subsequent vertical infiltration in favor of lateral runoff. On icy worlds such as Ganymede, landform degradation processes, such as mass wasting and impact erosion, could leave behind layered deposits of dark material of varying density and thickness. Therefore, characterizing such heterogeneity (layering) can reveal much about the different processes acting on the near-surface environment. These processes can be studied with a multi-frequency/bandwidth approach applied to surface radar reflectometry measurements.Airborne ice-penetrating radar, traditionally designed to study the subsurface of ice sheets on Earth, can also be used to study the surface and near-surface ice. Upcoming missions to the Jovian icy moons will carry ice-penetrating radars, namely the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) on the Europa Clipper mission and the Radar for Icy Moons Exploration (RIME) on the JUpiter ICy moons Explorer (JUICE) mission. REASON will operate at center frequencies of 60 MHz and 9 MHz, with bandwidths of 10 MHz and 1 MHz, respectively. RIME will operate with only a center frequency of 9 MHz but with dual-bandwidth capabilities of 2.8 MHz and 1 MHz.The Radar Statistical Reconnaissance method was applied to dual-frequency/bandwidth radar observations collected over Devon Ice Cap, Canadian Arctic, to deconvolve the total surface power into its coherent (Pc) and incoherent (Pn) components. Both Pc and Pn are used to map the spatial distribution and constrain the vertical thickness of ice layers embedded within firn. We extend this approach to Ganymede and assess its utility for studying near-surface layering in the context of rough surfaces. We simulate the radar surface echo with a generalized version of the multilayer Stratton-Chu coherent simulator previously published, but now compute the scattering contributions from every frequency component within the bandwidth of the emitted chirp. Simulated data are shown to validate the assumptions of the insensitivity to surface roughness parameters representative of Ganymede, when observing with different bandwidths but at the same center frequencies. Finally, we outline strategies for using RIME and REASON together for near-surface reflectometry studies over planned observations of the Jovian icy moons. Using observations obtained with the frequencies and bandwidths from both radars, particularly at crossover locations, can provide valuable knowledge of the near-surface structure, even when the surface may appear rough.

The discovery of Antarctica's deepest subglacial trough beneath the Denman Glacier, combined with high rates of basal melt at the grounding line, has caused significant concern over its vulnerability to retreat. Recent attention has therefore been focusing on understanding the controls driving Denman Glacier's dynamic evolution. Here we consider the Shackleton system, comprised of the Shackleton Ice Shelf, Denman Glacier, and the adjacent Scott, Northcliff, Roscoe and Apfel glaciers, about which almost nothing is known. We widen the context of previously observed dynamic changes in the Denman Glacier to the wider region of the Shackleton system, with a multi-decadal time frame and an improved biannual temporal frequency of observations in the last 7 years (2015–2022). We integrate new satellite observations of ice structure and airborne radar data with changes in ice front position and ice flow velocities to investigate changes in the system. Over the 60-year period of observation we find significant rift propagation on the Shackleton Ice Shelf and Scott Glacier and notable structural changes in the floating shear margins between the ice shelf and the outlet glaciers, as well as features indicative of ice with elevated salt concentration and brine infiltration in regions of the system. Over the period 2017–2022 we observe a significant increase in ice flow speed (up to 50 %) on the floating part of Scott Glacier, coincident with small-scale calving and rift propagation close to the ice front. We do not observe any seasonal variation or significant change in ice flow speed across the rest of the Shackleton system. Given the potential vulnerability of the system to accelerating retreat into the overdeepened, potentially sediment-filled bedrock trough, an improved understanding of the glaciological, oceanographic and geological conditions in the Shackleton system are required to improve the certainty of numerical model predictions, and we identify a number of priorities for future research. With access to these remote coastal regions a major challenge, coordinated internationally collaborative efforts are required to quantify how much the Shackleton region is likely to contribute to sea level rise in the coming centuries.

Understanding the past and future evolution of the Antarctic Ice Sheet is challenged by the availability and quality of observed paleo-boundary conditions. Numerical ice-sheet models often rely on these paleo-boundary conditions to guide and evaluate their models' predictions of sea-level rise, with varying levels of confidence due to the sparsity of existing data across the ice sheet. A key data source for large-scale reconstruction of past ice-sheet processes are internal reflecting horizons (IRHs) detected by radio-echo sounding (RES). When IRHs are isochronal and dated at ice cores, they can be used to determine paleo-accumulation rates and patterns on large spatial scales. Using a spatially extensive IRH over the Pine Island Glacier (PIG), Thwaites Glacier (THW), and the Institute and Möller ice streams (IMIS, covering a total of 610 000 km2 or 30 % of the West Antarctic Ice Sheet (WAIS)), and a local layer approximation model, we infer mid-Holocene accumulation rates over the slow-flowing parts of these catchments for the past ∼4700 years. By comparing our results with modern climate reanalysis models (1979–2019) and observational syntheses (1651–2010), we estimate that accumulation rates over the Amundsen–Weddell–Ross Divide were on average 18 % higher during the mid-Holocene than modern rates. However, no significant spatial changes in the accumulation pattern were observed. The higher mid-Holocene accumulation-rate estimates match previous paleo-accumulation estimates from ice-core records and targeted RES surveys over the ice divide, and they also coincide with periods of grounding-line readvance during the Holocene over the Weddell and Ross sea sectors. We find that our spatially extensive, mid-Holocene-to-present accumulation estimates are consistent with a sustained late-Holocene period of higher accumulation rates occurring over millennia reconstructed from the WAIS Divide ice core (WD14), thus indicating that this ice core is spatially representative of the wider West Antarctic region. We conclude that future regional and continental ice-sheet modelling studies should base their climatic forcings on time-varying accumulation rates from the WAIS Divide ice core through the Holocene to generate more realistic predictions of the West Antarctic Ice Sheet's past contribution to sea-level rise.

Introduction. Ganymede, Jupiter’s largest moon, is thought to have a salty subsurface ocean underlying an ice shell and may harbor the conditions to support life. The uppermost crust is mainly comprised of two types of terrain: heavily cratered, dark terrains and bright terrains often characterized by grooves [1]. The surface has also been subject to various landform degradation processes, such as mass movement, volatile segregation and migration, impact erosion, and regolith generation [2]. For example, such processes could be responsible for the formation of the dark deposits (layers) observed on Galileo Regio that vary in thickness (and other properties) as a function of their resting slope and position relative to local topographic crests, among other criteria [2]. Landform degradation processes thus can spatially alter the near-surface structure, characterized by different densities, impurities, and thicknesses (from tens to hundreds of meters). We present a radiometric approach for investigating the properties of near-surface layering at Ganymede from the combined observations of radar sounding systems that will reach the Jovian system within the next decade. Multi-frequency Radar Sounders. The JUpiter ICy moons Explorer (JUICE) from the European Space Agency (ESA) will be orbiting Ganymede by 2034. Its science payload includes the Radar for Icy Moons Exploration (RIME), a 9-MHz central frequency radar sounder with a 1-MHz (low resolution) or 3-MHz (high resolution) bandwidth (noted [9/1 MHz] and [9/3 MHz], respectively) [3]. Nearly concurrently, the Europa Clipper from the National Aeronautics and Space Administration (NASA), will perform flybys of Ganymede once to thrice, providing complementary observations from the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON), a dual frequency radar sounder at [60/10 MHz] and [9/1 MHz] [4]. This wealth of multi-frequency and multi-bandwidth observations is uniquely suited to constraining Ganymede’s near-surface properties through differential surface reflectometry. Reflectometry of Layered Near-surfaces. Reflectometry is related to the measurement of the radar surface echo strength that is sensitive to surface and near-surface properties with a footprint-size spatial resolution of several kilometers (depending on the spacecraft altitude) [5]. The near-surface depth is bounded by the vertical resolution defined from the bandwidth of the transmitted signal. In void, [60/10 MHz], [9/1 MHz] and [9/3 MHz] radar systems have a vertical resolution of 15 m, 50 m and 150 m, respectively [4]. The reflection strength of a homogeneous icy near-surface combined with a smooth surface is nearly independent of the radar system across the RIME-REASON frequency range. However, a sharp dielectric gradient from a horizontal discontinuity in the near-surface affects the effective surface reflection coefficient (Re) because of the phase shift between the surface and the near-surface reflections that are coherently integrated when measured at the receiver. Thin-film theory provides analytical tools to predict Re for layered media as a function of the layers’ thickness and permittivity, as well as the signal wavelength [6]. As an illustration, consider an overburden layer of unknown thickness (zlayer) and permittivity (εlayer), bounded by a void (ε0 = 1), and covering a compact ice substrate (εice = 3.1). Fig. 1 illustrates the field of solutions for Re computed for the three radar systems considered and assuming a synthetic chirp of 100 μs. Each plot on Fig. 1 is characterized by two regimes. When zlayer is larger than the near-surface depth, then the signal strength is independent of zlayer across all frequencies and only dependent on εlayer. Note in particular that as zlayer gets thinner than the near-surface depth, Re exhibits a resonant behavior strongly dependent on zlayer relative to the radio wavelength. Hence, multi-frequency observations can be overlapped, although the solutions are not necessarily unique. However, additional constraints like assumed lateral continuity of the near-surface structure can help resolve most ambiguities. In addition, surface roughness has a wavelength-dependent effect on surface reflectivity that can be difficult to deconvolve from the effect of near-surface layering. In that regard, because the [9/1 MHz] and [9/3 MHz] radar systems provide the same response to roughness (same radio wavelength), their response should differ only when layer boundaries are between their respective near-surface depths (different bandwidth). A strategy based on the combination of the reflectivity plots in Fig. 1 for the range of frequencies/bandwidths deployed on Ganymede can then be used to constrain its near-surface properties. An analog application on a terrestrial ice cap is provided in the next section. Proof-of-concept: Devon Ice Cap, Canadian Arctic. The near-surface of Devon Ice Cap (DIC) is subject to melting and refreezing processes, forming meters-thick ice layers embedded in lower porosity firn. The reflections from these layers from the surface down to the near-surface depth affect the coherent power (Pc) observed by a radar sounder (IPR). Fig. 2 illustrates a transect over DIC, where concurrent ground-penetrating radar (GPR) collected at 500 MHz and airborne IPR observations collected at [60/15 MHz] exist. Superimposed on the GPR radargram is a pink line that represents the frequency/bandwidth-constrained near-surface depth/vertical resolution of the airborne IPR. Results indicate that the behavior of Pc (green line) well correlates with the ice layer thickness within the near-surface depth and decorrelates below the near-surface depth at this frequency. Figure 1: Coherent surface echo strength (Re) as a function of an overburden thickness (zlayer) and permittivity (εlayer) covering an icy substrate (εice = 3.1) for REASON VHF [60/10 MHz], REASON HF [9/1 MHz], and RIME [9/3 MHz]. Figure 2: Observed coherent power and modeled reflectivity values (top), with concurrent GPR radargram (bottom) along a transect on Devon Ice Cap. References: [1] R. T. Pappalardo et al., Jupiter: The Planet, Satellites and Magnetosphere (2004), pp. 363– 396. [2] J. M. Moore et al., Icarus 140.2 (1999), pp. 294– 312. [3] L. Bruzzone et al., Proceedings of the IEEE 99.5 (2011), pp. 837–857. [4] C. Grima et al., Planetary and Space Science 117 (2015), pp. 421–428. [5] C. Grima et al., Planetary and Space Science 103 (2014), pp. 191– 204. [6] P. Yeh. Hoboken, New Jersey: John Wiley & Sons, Inc., 1998.

Melting and refreezing processes in the firn of Devon Ice Cap control meltwater infiltration and runoff across the ice cap, but their full spatial extent and effect on near-surface structure is difficult to measure with ground-based traverses or existing satellite remote sensing. Here, we derive the coherent component of the near-surface return from airborne ice-penetrating radar over Devon Ice Cap, Canadian Arctic, to characterize firn containing centimeter to meter-thick ice layers (i.e., ice slabs) formed from refrozen meltwater in firn. Comparison with reflectivities using a thin layer reflectivity model, informed by ground-based radar and firn core measurements, indicate that the coherent component is sensitive to the near-surface firn structure composed of quasi-specular ice and firn layers, limited by the bandwidth-constrained radar range resolution. By leveraging their differences in range resolution, we assess the use of dual-frequency airborne ice-penetrating radar to characterize the spatial and vertical near-surface structure of Devon Ice Cap. Our results suggest that average ice slab thickness throughout the Devon Ice Cap percolation zone ranges from 4.2 to 5.6 m. This implies conditions that can enable lateral meltwater runoff and potentially contribute to the total surface runoff routed through supraglacial rivers down glacier. Together with the incoherent component of the surface return previously studied, our dual-frequency approach provides an alternative method for characterizing bulk firn properties, particularly where ground-based and higher frequency radar data are not available.

Based on sparse data, Titan Dome has been identified as having a higher probability of containing ice that would capture the middle Pleistocene transition (1.25 to 0.7 Ma). New aerogeophysical observations (radar and laser altimetry) collected over Titan Dome, located about 200 km from the South Pole within the East Antarctic Ice Sheet, were used to characterize the region (e.g., geometry, internal structure, bed reflectivity, and flow history) and assess its suitability as a paleoclimate ice core site. The radar coupled with an available ice core chronology enabled the tracing of dated internal reflecting horizons throughout the region, which also served as constraints on basal ice age modeling. The results of the survey revealed new basal topographic detail and better constrain the ice topographical location of Titan Dome, which differs between community datasets. Titan Dome is not expected to be relevant to the study of the middle Pleistocene transition due to a combination of past fast flow dynamics, the basal ice likely being too young, and the temporal resolution likely being too coarse if 1 Ma ice were to exist.

Accreted ice retains and preserves traces of the ocean from which it formed. In this work, we study two classes of accreted ice found on Earth-frazil ice, which forms through crystallization within a supercooled water column, and congelation ice, which forms through directional freezing at an existing interface-and discuss where each might be found in the ice shells of ocean worlds. We focus our study on terrestrial ice formed in low temperature gradient environments (

Synthetic aperture radar (SAR) focusing will be a fundamental step in the analysis of the radar sounding datasets collected by the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instrument as part of NASA's upcoming Europa Clipper mission. Due to the flyby trajectory of the mission, REASON data acquisition will be distinct compared to other space-borne radar sounders, and therefore, require a tailored SAR focusing strategy. Here, we present a SAR focusing architecture based on the delay Doppler approach employed in US SHAllow RADar (SHARAD) data analysis with the following modifications for REASON data idiosyncrasies; an interpolation to a constant ground track interval to account for REASON's variable PRF; and an adaptive Doppler centroid estimation to account for the flyby geometry. The ability of our modified delay Doppler SAR focusing approach to focus space-borne datasets as well as its specific feasibility for REASON are demonstrated using both SHARAD and MARSIS datasets. In addition, we present a quantitative quality control framework based on pixel power probabilities and demonstrate how it can be leveraged to quantify the effects of SAR focusing and differentiate focused results generated with different processing parameters. Finally, we revisit and discuss the assumption of depth-independent SAR focusing implicit in the choice to construct a REASON SAR focusing approach based on the delay Doppler method and provide a comparison with depth-dependent SAR focusing for a simplified acquisition geometry.

A combination of aerogeophysics, seismic observations and direct observation from ice cores, and subglacial sampling, has revealed at least 21 sites under the West Antarctic Ice Sheet consistent with active volcanism (where active is defined as volcanism that has interacted with the current manifestation of the West Antarctic Ice Sheet). Coverage of these datasets is heterogeneous, potentially biasing the apparent distribution of these features. Also, the products of volcanic activity under thinner ice characterized by relatively fast flow are more prone to erosion and removal by the ice sheet, and therefore potentially under-represented. Unsurprisingly, the sites of active subglacial volcanism that we have identified often overlap with areas of relatively thick ice and slow ice surface flow, both of which are critical conditions for the preservation of volcanic records. Overall, we find the majority of active subglacial volcanic sites in West Antarctica concentrate strongly along the crustal-thickness gradients bounding the central West Antarctic Rift System, complemented by intra-rift sites associated with the Amundsen Sea–Siple Coast lithospheric transition.

We present a new simple and efficient method for correlation of unevenly and differently sampled data. This new method overcomes problems with other methods for correlation with non-uniform sampling and is an easy modification to existing correlation based codes. To demonstrate the usefulness of this new method to real-world examples, we apply the method with good success to two glaciological examples to map the ages from a well-dated ice core to a nearby core, and by tracing isochronous layers within the ice sheet measured from ice-penetrating radar between the two ice core sites.

Svenner Islands-Brattstrand Bluffs-Larsemann Hills constitutes ~70 km long coastal outcrops of Princess Elizabeth Land (PEL), comprising complexly deformed metapelites and orthogneisses. Pelitic granulites from these outcrops are investigated in this work. Conventional geothermobarometric estimations and Pseudosection modelling consistently indicate that the peak metamorphic grade throughout the area is high to ultra-high temperature (800–950 °C) at low to medium pressure (2–5 kbar). A high pressure (~10 kbar) relict metamorphic event and a substantial decompression component of ~5 kbar, corresponding to >15 km uplift, are inferred through petrographic as well as pseudosection analysis. Two set of ages are estimated (~800 Ma and ~500 Ma), corresponding to Tonian and Pan-African metamorphic events, respectively. Field data, petrographic studies and ages estimated from orthogneisses from the Brattstrand Bluffs and the Grovnes Peninsula suggest that this unit is a product of in-situ melting of the pelitic granulites. Pelitic granulites of PEL possess similarities with those exposed in the Eastern Ghat Mobile Belt of India. We propose that these sectors represent a contiguous terrane with two major orogenic imprints, reflecting Rodinia and Gondwana amalgamations. An attempt is made to mark out paleo-orogenic belt axes, supported by both field as well as recent aero-magnetic signatures in interior PEL. We support that the parent sediments of the pelitic granulites were deposited during Stenian period, which underwent compressional UHT-HP(?) metamorphism at ~800 Ma. Another extensive basin is proposed at ~600 Ma prior to the Pan-African orogenic event. We propose that the Pan-African orogeny marked the collision of Indo-Australo-Africo-Antarctic cratons and stitched the East Gondwana. We also propose a thinned lithosphere along the system of subglacial lakes-canyons confirmed by ICECAP data. Analog modelling is used to demonstrate the influence of pervasive mechanical anisotropy of the basement in defining the orientation of this rift system and its connection to the Lambert Graben.

The seafloor topography under the Amery Ice Shelf steers the flow of ocean currents transporting ocean heat, and thus is a prerequisite for precise modeling of ice-ocean interactions. However, hampered by thick ice, direct observations of sub-ice-shelf bathymetry are rare, limiting our ability to quantify the evolution of this sector and its future contribution to global mean sea level rise. We estimated the seafloor topography of this region from airborne gravity anomaly using simulated annealing. Unlike the current seafloor topography model which shows a comparatively flat seafloor beneath the calving front, our estimation results reveal a 255-m-deep shoal at the western side and a 1,050-m-deep trough at the eastern side, which are important topographic features controlling the ocean heat transport into the sub-ice cavity. The gravity-estimated seafloor topography model also reveals previously unknown depressions and sills in the middle of the Amery Ice Shelf, which are critical to an improved modeling of the sub-ice-shelf ocean circulation and induced basal melting. With the refined seafloor topography model, we anticipate an improved performance in modeling the response of the Amery Ice Shelf to ocean forcing.

Atmospheric warming has led to increased surface melting on glaciers in the Arctic. This meltwater can percolate into firn and refreeze to form ice layers. Depending on their thickness, low-permeability ice layers can act as barriers that inhibit subsequent vertical meltwater infiltration in deeper firn pore space and favor lateral meltwater runoff. Thus, characterizing ice layers in firn is key for understanding the near-surface hydrological conditions that could promote surface meltwater runoff and its contribution to sea level rise.Airborne ice-penetrating radar (IPR) is a powerful tool for imaging subsurface structure, but only recently have these systems been applied to direct observations of the bulk properties of the near-surface. To evaluate the bulk permeability of the near-surface firn system of Devon Ice Cap (DIC), Canadian Arctic, we use the Radar Statistical Reconnaissance (RSR) technique, originally developed for accumulation studies in West Antarctica. This method utilizes both the coherent and incoherent components of the total surface return, which are predominately sensitive to near-surface permittivity/structure within the system’s vertical range resolution and surface roughness, respectively. Here, we apply RSR to IPR data collected over DIC with the High-Capability Airborne Radar Sounder 2 (HiCARS) system (60 MHz center-frequency, 15 MHz bandwidth), operated by the University of Texas Institute for Geophysics (UTIG). Guided by ground-based ice-penetrating radar data and firn core density measurements, we show that the near-surface heterogeneous firn structure, featuring ice layers, mainly affects the observed coherent component.We further compare the coherent component of HiCARS with that derived from IPR data collected with the University of Kansas Multichannel Coherent Radar Depth Sounder (MCoRDS) 3 system (195 MHz center-frequency; 30 MHz bandwidth), to evaluate the utility of dual-frequency IPR for characterizing near-surface ice layers. We expect that each radar system is sensitive to a different scale of near-surface bulk properties (i.e., depth and thickness of ice layers of different vertical extents), governed by each radar systems’ center frequency and bandwidth-limited range resolution. We leverage these differences in range resolution to derive ice layer thickness constraints in the DIC firn zone containing meter-thick ice layers, which are consistent with ground-based observations. Our results suggest this dual-frequency approach does indeed show that ice layers are vertically resolvable, spatially extensive, and mostly impermeable to surface meltwater. Thus, we hypothesize that lateral flow over high elevation meter-thick ice layers may contribute to the total surface runoff routed through supraglacial rivers down-glacier in the ablation zone.

The Princess Elizabeth Land sector of the East Antarctic Ice Sheet is a significant reservoir of grounded ice and is adjacent to regions that experienced great change during Quaternary glacial cycles and Pliocene warm episodes. The existence of an extensive subglacial water system in Princess Elizabeth Land (to date only inferred from satellite imagery) bears the potential to significantly impact the thermal and kinematic conditions of the overlying ice sheet. We confirm the existence of a major subglacial lake, herein referred to as Lake Snow Eagle (LSE), for the first time using recently acquired aerogeophysical data. We systematically investigated LSE’s geological characteristics and bathymetry from two-dimensional geophysical inversion models. The inversion results suggest that LSE is located along a compressional geologic boundary, which provides reference for future characterization of the geologic and tectonic context of this region. We estimate LSE to be ~42 km in length and 370 km2 in area, making it one of the largest subglacial lakes in Antarctica. Additionally, the airborne ice-penetrating radar observations and geophysical inversions reveal a layer of unconsolidated water-saturated sediment around and at the bottom of LSE, which—given the ultralow rates of sedimentation expected in such environments—may archive valuable records of paleoenvironmental changes and the early history of East Antarctic Ice Sheet evolution in Princess Elizabeth Land.