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Seismic travel time inversion code from: Geophysical evidence of tectonic structures beneath Thwaites Glacier, West Antarctica: influence on glacier dynamics. Submitted to Journal of Geophysical Research: Solid Earth 

Flexure modeling code for manuscript: Geophysical evidence of tectonic structures beneath Thwaites Glacier, West Antarctica: influence on glacier dynamics. Submitted to Journal of Geophysical Research: Solid Earth 

Results from seismic travel time inversion and potential fields modeling in: Geophysical evidence of tectonic structures beneath Thwaites Glacier, West Antarctica: influence on glacier dynamics 

Basal conditions that facilitate fast ice flow are still poorly understood and their parameterization in ice‐flow models results in high uncertainties in ice‐flow and consequent sea‐level rise projections. Direct observations of basal conditions beneath modern ice streams are limited due to the inaccessibility of the bed. One approach to understanding basal conditions is through investigating the basal landscape of ice streams and glaciers, which has been shaped by ice flow over the underlying substrate. Bedform variation together with observations of ice‐flow properties can reveal glaciological and geological conditions present during bedform formation. Here we map the subglacial landscape and identify basal conditions of Rutford Ice Stream (West Antarctica) using different visualization techniques on novel high‐resolution 3D radar data. This novel approach highlights small‐scale features and details of bedforms that would otherwise be invisible in conventional radar grids. Our data reveal bedforms of <300 m in length, surrounded by bedforms of >10 km in length. We correlate variations in bedform dimensions and spacing to different glaciological and geological factors. We find no significant correlation between local (<3 × 3 km) variations in bedform dimensions and variations in ice‐flow speed and (surface or basal) topography. We present a new model of subglacial sediment discharge, which proposes that variations in bedform dimensions are primarily driven by spatial variation in sediment properties and effective pressure. This work highlights the small‐scale spatial variability of basal conditions and its implications for basal slip. This is critical for more reliable parameterization of basal friction of ice streams in numerical models. 

Abstract Thwaites Glacier in West Antarctica has been identified as a route to destabilization of the whole West Antarctic Ice Sheet, potentially leading to several meters of sea‐level rise. However, future evolution of Thwaites Glacier remains uncertain due to a lack of detailed knowledge about its basal boundary that will affect how its retreat proceeds. Here we aim to improve understanding of the basal boundary in the lower part of Thwaites Glacier by modeling the crustal structures that are related to the bed‐type distribution and therefore influence the basal slip. We combine long‐offset seismic, and gravity‐ and magnetic‐anomaly data to model the crustal structures along two 120 km lines roughly parallel to ice flow. We find a sedimentary basin 40 km in length in the along‐flow direction, with a maximum thickness of 1.7 0.2 km, and two mafic intrusions at 5–10 km depth that vary in maximum thickness between 3.8 and 8.6 km. The sedimentary basin and major mafic intrusions we modeled are likely related to the multi‐stage tectonic evolution of the West Antarctic Rift System. Thwaites Glacier flows across a tectonic boundary within our study site, indicating it flows across tectonically formed structures. The varying geology and resulting variations in bed types demonstrate the influence of tectonics on Thwaites Glacier dynamics. 

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.