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Abstract Hercules Dome is a prospective ice‐core site due to its setting in the bottleneck between East and West Antarctica. If ice from the last interglacial period has been preserved there, it could provide critical insight into the history of the West Antarctic Ice Sheet. The likelihood of a continuous, well‐resolved, easily interpretable climate record preserved in ice extracted from Hercules Dome depends in part on the persistence of ice‐flow dynamics at the divide. Significant changes in ice drawdown on either side of the divide, toward the Ross or Ronne ice shelves, could change the relative thickness of layers and the deposition environment represented in the core. Here, we use radar sounding to survey the ice flow at Hercules Dome. Repeated radar acquisitions show that vertical velocities are consistent with expectations for an ice divide with a frozen bed. Polarimetric radar acquisitions capture the ice‐crystal orientation fabric (COF) which develops as ice strains, so it depends on both the pattern of ice flow and the time over which flow has been consistent. We model the timescales for COF evolution, finding that the summit of Hercules Dome has been dynamically stable in its current configuration, at least over the last five thousand years, a time period during which the Antarctic ice sheet was undergoing significant retreat at its margins. The evident stability may result from a prominent bedrock ridge under the divide, which had not been previously surveyed and has therefore not been represented in the bed geometry of coarsely resolved ice‐sheet models. 

Abstract Subglacial lakes require a thawed bed either now or in the past; thus, their presence and stability have implications for current and past basal conditions, ice dynamics, and climate. Here, we present the most extensive geophysical exploration to date of a subglacial lake near the geographic South Pole, including radar‐imaged stratigraphy, surface velocities, and englacial vertical velocities. We use a 1.5‐dimensional temperature model, optimized with our geophysical data set and nearby temperature measurements, to estimate past basal‐melt rates. The ice geometry, reflected bed‐echo power, surface and vertical velocities, and temperature model indicate that the ice‐bed interface is regionally thawed, contradicting prior studies. Together with an earlier active‐source seismic study, which showed a 32‐m deep lake underlain by 150 m of sediment, our results suggest that the lake has been thermodynamically stable through at least the last 120,000 years and possibly much longer, making it a promising prospective site for sediment coring. 

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. 

{"Abstract":["This archive includes data and ipython notebooks to create the figures for the manuscript "Response of water isotopes in precipitation to a collapse of the West Antarctic Ice Sheet in high-resolution simulations with the Weather Research and Forecasting Model" submitted to Journal of Climate in August 2022.<\/p>\n\nModel output from WRFwiso and iCAM is in data.zip (saved as monthly means)<\/p>\n\nNotebooks and python modules are in scripts.zip<\/p>\n\nRequired python packages (all included in environment.yml):<\/p>\n\nnumpy<\/li>matplotlib<\/li>netcdf4<\/li>basemap<\/li>scipy<\/li>wrf-python<\/li>windspharm<\/li>metpy<\/li>intergrid<\/li>cmocean<\/li><\/ul>"]} 

Abstract All radar power interpretations require a correction for attenuative losses. Moreover, radar attenuation is a proxy for ice-column properties, such as temperature and chemistry. Prior studies use either paired thermodynamic and conductivity models or the radar data themselves to calculate attenuation, but there is no standard method to do so; and, before now, there has been no robust methodological comparison. Here, we develop a framework meant to guide the implementation of empirical attenuation methods based on survey design and regional glaciological conditions. We divide the methods into the three main groups: (1) those that infer attenuation from a single reflector across many traces; (2) those that infer attenuation from multiple reflectors within one trace; and (3) those that infer attenuation by contrasting the measured power from primary and secondary reflections. To assess our framework, we introduce a new ground-based radar survey from South Pole Lake, comparing selected empirical methods to the expected attenuation from a temperature- and chemistry-dependent Arrhenius model. Based on the small surveyed area, lack of a sufficient calibration surface and low reflector relief, the attenuation methods that use multiple reflectors are most suitable at South Pole Lake. 

Abstract Despite widespread use of radio-echo sounding (RES) in glaciology and broad distribution of processed radar products, the glaciological community has no standard software for processing impulse RES data. Dependable, fast and collection-system/platform-independent processing flows could facilitate comparison between datasets and allow full utilization of large impulse RES data archives and new data. Here, we present ImpDAR, an open-source, cross-platform, impulse radar processor and interpreter, written primarily in Python. The utility of this software lies in its collection of established tools into a single, open-source framework. ImpDAR aims to provide a versatile standard that is accessible to radar-processing novices and useful to specialists. It can read data from common commercial ground-penetrating radars (GPRs) and some custom-built RES systems. It performs all the standard processing steps, including bandpass and horizontal filtering, time correction for antenna spacing, geolocation and migration. After processing data, ImpDAR's interpreter includes several plotting functions, digitization of reflecting horizons, calculation of reflector strength and export of interpreted layers. We demonstrate these capabilities on two datasets: deep (~3000 m depth) data collected with a custom (3 MHz) system in northeast Greenland and shallow (<100 m depth, 500 MHz) data collected with a commercial GPR on South Cascade Glacier in Washington.