Reconstructing the past topography of Antarctica and its influence on ice sheet behaviour

Abstract

The development of accurate predictions of the response of the Antarctic Ice Sheet to future climatic change is a key challenge facing the scientific community. Ice sheet models are typically evaluated with recourse to how well they can reproduce past ice sheet behaviour, which is constrained by geological data. However, subglacial topography, an important boundary condition in numerical ice sheet models, may have evolved significantly through time due to processes such as tectonics and erosion. It is therefore necessary to use a topographic reconstruction to more accurately simulate past ice sheet dynamics for a particular time interval. This will, in turn, engender increased confidence in the models used to predict future ice sheet behaviour and sea level change.

This thesis develops a workflow tailored towards elucidating changes to Antarctica's subglacial topography since glacial inception at the Eocene-Oligocene boundary (ca. 34 million years ago). The thesis targets three regions in East Antarctica: the Recovery catchment, Wilkes Subglacial Basin, and Pensacola-Pole Basin. These areas are chosen because each is characterised by extensive areas of topography situated below present-day sea level, which renders the overlying ice sheet potentially vulnerable to rapid and extensive change. In addition, each area presents the opportunity to, for the first time, combine recently acquired geophysical datasets with onshore and offshore geological constraints to develop models of long-term landscape evolution.

The findings of these regional studies are combined and the workflow is expanded across the continent to produce new reconstructions of Antarctic topography at four climatic intervals: (1) the Eocene-Oligocene boundary (ca. 34 Ma); (2) the Oligocene-Miocene boundary (ca. 23 Ma); (3) the mid-Miocene climate transition (ca. 14 Ma); and (4) the mid-Pliocene warm period (ca. 3.5 Ma). These reconstructions reveal that the area of land above sea level at ca. 34 Ma was ~25% greater than today. Large areas in West Antarctica and around the East Antarctic margin subsequently became lower-lying due to glacial erosion and thermal subsidence. Ice sheet models using these new topographies indicate that the Antarctic Ice Sheet has become more sensitive to climate and ocean forcing through time as a result of landscape evolution processes. Use of these topographies in the next generation of ice sheet models will improve confidence in the understanding of Antarctic Ice Sheet sensitivity to past, present and future climatic change.