Evidence of Dynamic Thinning and Grounding Line Retreat over the Last Two Decades in Porpoise Bay, Wilkes Land, East Antarctica

Over the last four decades, the Antarctic Ice Sheet has been losing mass, largely from West Antarctica. Though the East Antarctic Ice Sheet (EAIS) is often considered less vulnerable to climate change, recent studies suggest that some regions of the EAIS have lost mass at accelerating rates over recent decades. In particular, Wilkes Land, which overlies the marine-based Aurora Subglacial Basin, has been referred to as the ‘weak underbelly’ of the EAIS. Whilst several large outlet glaciers drain this region, few have been studied in detail, including the four glaciers that drain Porpoise Bay. This thesis presents new data on the understudied Porpoise Bay outlet glacier dynamics observed between 1963 and 2025. Optical satellite imagery, differential synthetic aperture radar interferometry, and a range of previously published datasets are used to explore changes in the ice-shelf front, grounding line position, ice surface velocity and ice surface elevation over the last three decades. The results reveal evidence of dynamic changes in the region, characterised by extreme thinning of grounded ice and rapid grounding line retreat, albeit with large uncertainties, across Holmes East and West glaciers and Frost Glacier. This thesis finds that Holmes West Glacier was recently grounded at the edge of a steep retrograde slope that continues inland for tens of kilometers. Rapid grounding line retreat may therefore be predicted at this glacier over the coming decades. Analysis of ocean temperatures and salinity are consistent with the notion that warm Circumpolar Deep Water proximal to the continental shelf break could access the glaciers through deep cross-shelf troughs, which could drive the previously estimated high rates of basal melting beneath their floating tongues/ice shelves. Observations of ice-shelf frontal change and sea-ice concentration across Porpoise Bay’s ice shelves support a previous study of near-synchronous ice-shelf calving that correlates with the break-out of sea ice. This study finds an additional recent calving event, further highlighting the vulnerability of this region to ongoing and future changes in ocean and sea-ice conditions.