GEO ICE - Benchmark Geological Records for the Response of the West Antarctic Ice Sheet to Near Future Temperature

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

Abstract

The Paris Agreement presents humanity with an ambitious and critical goal: to keep global warming well below 2 degrees above pre-industrial levels. All 197 countries have signed up, and 189 have formally approved it. But there is no doubt that these targets present a massive challenge, and a certain amount of environmental change is already inevitable.

We know that sea level will rise 10s of centimetres over the next several decades, displacing many millions of people living in low lying coastal areas. But we don't yet know just how much more our seas will rise through the coming centuries. Will our efforts to curb emissions stop the collapse of Antarctica's ice shelves and loss of the West Antarctic Ice Sheet? Under which conditions does collapse occur? And which part of the ice sheet will react first? Computer models yield conflicting results on these questions, partly because they simulate the past (and our future) using different environmental conditions and model physics. To figure out which of these are right, we need to obtain observational data from the geological past to test the models.

Our project will embark in a detective story to provide some long-searched for evidence. We will exploit two geological records to reconstruct West Antarctic Ice Sheet history under temperatures only slightly elevated above modern levels (i.e. late Pleistocene interglacials). The first of these records comes from a recent ship-based drilling campaign (International Ocean Discovery Program Expedition 374) that recovered mud and sand from the Ross Sea, an area right next to the West Antarctic Ice Sheet. The second record will be retrieved from an ice shelf-based drilling rig that will recover the first extended record of sub-seafloor mud and sand from far beneath the Ross Ice Shelf, at a location where the West Antarctic ice sheet detaches from the seafloor and starts to float into the Ross Sea (Siple Coast drilling).

For our first work package, we will analyse the chemical composition of mud, sand and organic particles to reconstruct critical environmental conditions. Firstly, the mud and sand will uncover where on the continent the pieces of rocks came from. Knowledge of the location of erosion can then tell us in turn whether the West Antarctic Ice Sheet melted during past times when temperatures were just a little bit warmer than today, or not. Secondly, the chemical composition of organic particles in the same samples will reveal prevailing ocean temperatures at the time of deposition. Thirdly, the presence/absence of certain types of marine algae will tell us whether floating ice was present or not. The combination of the three different sets of data will help us unravel where geographically ice melting started in West Antarctica.

For our second work package, we will utilise our new data to test coupled ice sheet-climate models, which are also used to predict future sea level. Assessing how well these models perform in simulating the geological past is a key way of determining how accurate their projections of the future are. In detail we will test two such models, called PSUICE3D and BISICLES. We will analyse existing model simulations that led to collapse of the West Antarctic Ice Sheet during past warm times, and perform new simulations using a more realistic environmental framework constrained by our new data.

The comparison of predicted places of ice retreat and modelled places of ice retreat has never been realised before and will allow us to pinpoint which parts of Antarctica are most vulnerable to moderate levels of global warming, providing vital information towards mitigation and adaptation of sea level rise for settlements in coastal areas around the globe.

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