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ApRES on Thwaites Glacier

A map of ApRES point and polarmetric sites along Thwaites Glacier, showing our traverse route for the 2022-23 field season.
Thwaites is one of Antarctica’s most rapidly changing glaciers, losing mass (ice) at a rate of ~50 gigatons per year. In 2017, the International Thwaites Glacier Consortium began, bringing together 8 project teams across disciplines and countries to study the past, present, and future of this region.

In 2022-2023, as part of the G.H.O.S.T. team, I took ~250 phase-sensitive radar (ApRES) measurements along a 200 km transect running up the center of Thwaites. Over the course of 11 working days, we traveled by pisten bully and skidoo upglacier to obtain point and polarmetric ApRES measurements.
Collaborators: Andrew Hoffman, Knut Christianson, Florian Koch, Ole Zeising, Catrin Thomas, Peter Young, Dave Jamison, Louise Borthwick, Rebecca Pearce, Jonny Kingslake, and the rest of the G.H.O.S.T. team

Point measurements, repeated from one year to the next, allow us to calculate the englacial strain rate. The englacial strain rate tells us how the glacier is stretching or squashing in the vertical, which gives us some information about how it is responding to stresses like bed topography. We will repeat the first season’s point measurements in 2023-2024.

Polarmetric measurements show us the ice fabric. A glacier is made up of ice crystals, water molecules frozen into a hexagonal crystal lattice. As the glacier undergoes various stresses - gravity pulling it down, snow falling on top - the ice crystals rotate in response. The bulk orientation of these ice crystals is called the ice fabric. The ice fabric records the history of stress undergone by the ice, and affects the ice’s current visocsity (how easily it flows given a force in a particular direction) and permittivity (how easily the ice allows radio waves to pass). By turning the antennas to send out polarized waves along orthogonal planes, we can reconstruct the ice fabric, which we can use to inform glacier models.

Continuous measurements require the ApRES to be left for extended periods, and allow us to measure how englacial strain rates (including firn densification) and subglacial conditions change over time.  In collaboration with Knut Christianson and Andrew Hoffman, we buried two ApRES over Subglacial Lake 142 and a third at Lower Thwaites Camp, and will collect them in the 2023-24 season.