Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica

Differential interferometry measures a differential change in ice displacement between 3 (or 4) epochs after eliminating the horizontal motion of ice through differencing of two pairs: we subtract two consecutive one-day pairs to eliminate the (steady) horizontal motion of the ice and leave the short term (vertical) motion of the ice, i.e. the vertical motion caused by changes in oceanic tide and atmospheric pressure, plus noise. If there is a data gap in data acquisition, we combine 2 x 1-day pairs acquired more than one day apart, hence 4 scenes. Predictions of SSH. We calculate changes in SHH using the CATS2008 tidal model corrected for IBE using ERA-5 atmospheric pressure fields. Subglacial hydrology is reproduced using the 2D finite-element Glacier Drainage System (GlaDS) model, which predicts the presence of long, high-pressured subglacial channels and an adjacent distributed drainage system. GlaDS calculates water discharge, flux, and pressure beneath Thwaites Glacier. The model allows coincident development of distributed and channelized systems. We test a range of conductivity of the distributed and channelised systems to converge to a stable solution. We use outputs that produce a) an upper limit for water pressure, beyond which the model does not converge, b) a lower limit when solutions have water with pressures far below the overburden pressure, and c) intermediate levels of pressure. We present an output (c) with a distributed system conductivity of 1 x 10-4 m3/2 kg-1/2 and a channel conductivity of 5 x 10-2 m3/2 kg-1/2. The model is applied with basal sliding velocity and water production (geothermal and frictional heat) from the ISSM IMSIP-6 Antarctic control run along with surface and bed topographies from BedMachine Antarctica version 1. The model is run on a mesh of 19,340 nodes with refining near the grounding line giving a minimum edge length of 280 m. The model is run for 20,000 days until near steady state.