The influence of evolving bed topography on marine ice stream stability.

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The future stability of the Antarctic and Greenland Ice Sheets is important due to the risk of sea-level rise in a warming climate. However, the controls on ice sheet behavior are not fully understood. One potential control that has received less attention than it should is the importance of continuously evolving bed topography. This study aims to test how ice sheets respond to patterns of evolving subglacial topography via the processes of glacial erosion and deposition. Observations suggest that erosion and deposition can rapidly and significantly change the shape of the landscape under the ice. These changes may have an impact on the behavior of the overlying ice on timescales of decades to centuries and beyond. For example, geological data and theory suggests that erosion may destabilise ice streams and lead to rapid ice sheet retreat whereas deposition may enable an ice stream to stabilise or advance. The approach of this project is to construct a computer model that integrates the ability to erode and deposit sediment underneath an ice stream, with the ability to monitor how the ice stream responds. Such a model has not been developed before, despite the potential importance of erosion and deposition to control the sensitivity of an ice-sheet to changes in climate or sea level. This project therefore targets a potentially critical question for future ice-sheet behavior. It is made possible by the collection of significant volumes of data that help quantify how fast, and in what pattern erosion and deposition can occur. These data, provided by collaborators from all over the world, can be used to control the model so that realistic, robust and repeatable simulations can be carried out. This is important for having confidence in the model's ability to capture and predict the real sensitivity of ice streams to different control factors.The model will be used to ask 3 key questions:1) Can the deposition of wedges of sediment at the transition between grounded and floating ice stabilise ice streams against future sea-level rise and climate warming?2) Can glacial erosion drive ice stream retreat, and if so, over what timescales?3) How might the Whillans Ice Stream in West Antarctica respond to erosion and deposition in the future as sea levels rise and the climate warms?The Whillans Ice Stream is used here as a test-case because it is the focus of a major effort to understand the subglacial conditions of an ice stream. As a result, it is one of the best monitored modern systems, with data on ice flow, basal erosion and deposition that will be used to construct a simulation of present-day behavior. This robustly controlled modern simulation will form the starting point for experiments that go on to predict future behavior. The outcome of this project will be to identify whether evolving basal topography is important for ice stream stability on timescales of decades, centuries, millennia or glacial cycles. Equally, it may identify that erosion and deposition, despite being widespread processes, do not significantly impact upon ice-stream behavior. The establishment of any of these outcomes will be a significant benefit, enabling future studies of ice stream stability to incorporate evolving basal conditions as appropriate. As a result, this project will refine our understanding of what controls ice stream behavior and thereby improve predictive capabilities in the context of a warming world.