Antarctic grounding line migration from satellite laser altimetry

In this thesis I present new methods and observations to improve our understanding of the patterns and drivers of Antarctic grounding line (GL) migration over various time-scales, using satellite laser altimetry and other satellite datasets.

First, I develop a new method to measure short-term, tidal GL migration using ICESat-2 repeat-track laser altimetry (RTLA), locating the GL position at multiple individual tidal states along the same satellite track. Applied to the grounding zone (GZ) of the Bungenstockrücken ice plain, this technique identifies a 1,300 km2 area of ephemeral grounding over which the GL migrates by up to 15 km between low and high tide, and reveals four distinct modes of tidal migration: “linear”, “asymmetric”, “threshold” and “hysteresis”. I also combine this technique with differential synthetic aperture radar interferometry (DInSAR) to reveal the ungrounding of an ice plain on the Ross Ice Shelf over 15 years.

Next, I present a 21-year time series of subglacial lake activity at Engelhardt Subglacial Lake (SLE) in West Antarctica, compiled from ICESat, ICESat-2 and CryoSat-2 altimetry. I document, for the first time, the second drainage of this lake on record, beginning in July 2021, and detect up to 13 km of GL retreat downstream of the lake over the same period with a combination of ICESat-2, DInSAR and high-resolution digital elevation model (DEM) data. Using these observations, I evaluate the mechanism triggering SLE drainage, the cause of the observed GL retreat, and the interplay between subglacial hydrology and GL dynamics.

Finally, I map the spatial distribution and shape of wave-like surface features (WSFs) associated with the basal stress transition around the Ross Ice Shelf GZ, using DEM and ICESat-2 data. I demonstrate that satellite observations of WSFs, combined with viscous beam theory, can improve estimates of GL location, basal properties, and ice thickness in Antarctic GZs.