Basal Conditions on Rutford Ice Stream: Bed Access, Monitoring and Ice Sheet History

The Antarctic and Greenland ice sheets play a major role in controlling Earth's sea level and climate, but our understanding of their history and motion is poor. At the moment, the biggest uncertainty in our ability to predict future sea level comes from these ice sheets. This is particularly important because sea level rise from ice sheets is increasing faster than expected, and because ice sheets have the potential to trigger irreversible sea level rise that would continue for many centuries. Reducing this uncertainty is currently one of the biggest challenges in glaciology. Our project aims to improve our understanding of two aspects of this uncertainty: first, the past behaviour of the West Antarctic Ice Sheet (WAIS), and second, the flow of the fast ice streams that drain it. By choosing the right location, we can address both these aims within one project. Rutford Ice Stream is one of the large, fast-flowing glaciers that drain WAIS and deliver the ice to the ocean. It has the advantage that a large amount of data have already been collected there from surface fieldwork, from aircraft, and from satellites. The next step is to access the ice stream bed directly, and the existing data mean we can identify the optimum locations for this. Using a hot-water drill we will make holes to the bed of the ice stream, through ice more than 2 km thick. Once the drill reaches the bed we will collect samples of sediment from beneath the ice. We will also collect sections of ice core from the ice column. Strings of instruments will be lowered down the holes to measure the pressure in the water system beneath the ice, the temperature profile in the ice and the way the ice deforms as it flows downstream. We will also insert probes into the bed that will measure how fast the ice is sliding, as well as the strength of the sediment in the bed itself. Borehole video cameras will record the nature of the ice, bed and water system, including how much sediment is frozen into the bottom of the ice. On the ice stream surface we will carry out a number of geophysical experiments designed to study the flow of the ice and to map the topography and the variations in basal water and sediment in the area around the drill holes. This will help us to interpret the measurements made in the drill holes. GPS receivers will track the motion of the ice surface; seismic surveys will map the softer and harder areas of bed sediment; radar surveys will show where water beneath the glacier is concentrated or distributed; and a seismometer array will detect the noise bursts emitted as the ice stream grinds over its bed. Project results will be analysed at the British Antarctic Survey, Swansea University and NERC-GEF. Other project partners at NASA-JPL, University College London and the University of Bristol will also contribute. When completed, the project will give information on: - An age for the most recent collapse of the ice sheet in this region - The water system beneath the ice - The thermal regime of the ice and bed - The partition of ice motion between the three different flow mechanisms - sliding, ice deformation and bed deformation The timing of the last ice sheet collapse will be extremely valuable because no other information yet exists in this region. It will help us to understand the way the ice sheet has changed as climate has warmed and cooled in the past. Our other results - characterising ice stream dynamics and how ice, water and the sedimentary bed interact - will help us understand the processes by which ice streams move, and how we should include these processes into models. The results will help to clarify previous work from ice streams elsewhere in Antarctica, which in some cases have been contradictory or inconclusive. Overall, these results will be big steps forward in our ability to understand the way ice sheets behaved in the past, what controls them today, and how they might evolve in the future.