Testing smaller-than-present configurations of the Antarctic Ice Sheet using a novel integration of geochronology

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The Antarctic Ice Sheets (East Antarctica and West Antarctica) hold enough fresh water to raise global sea levels by over 60 m. Even a partial collapse of the West Antarctic Ice Sheet, by far the smaller of the two, could raise sea level by 2-3 m displacing many millions of people and forcing them to find new places to live inland. It is known that the Antarctic Ice Sheets are losing mass at an increased rate meaning they are heading to a configuration that is smaller than present. To understand how such a configuration is reached it is vital to understand ice sheet behavior at times in the past when they were smaller than present.Computer models of ice sheet behaviour are capable of making predictions but require observations for validation and improvement. One way of doing this is to test whether the models accurately reproduce behaviours observed in reality. The limited areas of Antarctica that are not ice covered have yielded vital information on past ice sheet extents but can only inform on larger than present ice sheet configurations. To understand smaller than present configurations this proposal will access rock that is now covered by ice. This rock retains measureable properties that record when it was last uncovered by the ice sheet allowing the timing and duration of these events to be determined. This project will collect sub-glacial samples from a key region of West Antarctica, the Weddell Sea. In this area recent work using radar has identified internal structures within the ice sheet that suggests it has undergone recent change. Specifically, the data is consistent with the ice sheet having expanded over the last few hundreds of years following a period of time where it was smaller than present. Understanding the current state of the ice sheet and the process that control its behaviour is key to making predictions about how it will respond to human induced global warming. I will use a portable drill system to drill through ice close to present day mountains that protrude above the ice sheet. Over the course of two Antarctic field seasons the drill will be used to collect a series of sub-glacial rock cores that will be returned to laboratories where a novel combination of geochronological methods will be employed to establish if the rock has previously been exposed due to the ice sheet being smaller. By combining different techniques I will improve the constraints that can be obtained; thus not only can it be established if the ice sheet was smaller in the past but also when, and for how long, this was the case. I will then use the new data to evaluate computer models of ice sheet behaviour. These models use combinations of parameter values, representing processes that occur in reality, to produce simulations of ice sheet behaviour through time. By exploring a range a different parameter values large collections of simulations (ensembles) define a range of potential ice sheet simulations that may or may not closely reflect reality. The new geological data is a product of the actual ice sheets behaviour and can be used to sieve out model simulations that are far from reality. Remaining simulations can be scored according to how closely they match the geological data. In this way I will determine what parameters (i.e. what processes) are key to controlling ice sheet behaviour. In this way my project will bring about a step-change in our understanding of processes that control ice sheet behaviour on short geological timescales. Furthermore, the refined ice sheet history and model parameter ranges identified in this project will improve future modelling efforts and lead to more precise predictions of future ice sheet behaviour and associated sea level rise.