Ice Fabric on Thwaites Glacier from ApRES Polarimetric Measurements

Thwaites Glacier (TG) is a wide, fast moving ice stream that, along with Pine Island Glacier, drains much of the West Antarctic Ice Sheet (WAIS). This work presents preliminary results of ice fabric, bed topography, and englacial layering from a 200-km-long Autonomous phase-sensitive Radio Echo Sounder (ApRES) survey along the trunk of TG as part of the International Thwaites Glacier Consortium’s GHOST project in 2022-2023. From 235 point measurements and 47 polarimetric measurements, we find a variable, complex ice fabric that changes in strength and orientation along the transect and with depth. Fabric strength, measured as horizontal anisotropy, is on average stronger downstream than upstream, and the fast axis (also known as the symmetry axis) is more aligned along flow than across, as expected in an ice stream. Ice fabric is useful to both meaure and model because it both serves as a record of past stress and deformation, and affects viscosity, directionally softening the ice and impacting the glacier’s response to future stresses.