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

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.

Users:
The beneficiaries outside the academic realm are school teachers and young people in the North East of England. These communities will benefit culturally from this work by gaining a better understanding of what science is doing to understand how and why ice sheets, sea level and climate are changing. The benefits will be felt at a local and regional scale in the North East of England via collaboration and interaction with the multi award-winning Climate Change Schools Project (CCSP). In addition, as outlined below, the work will impact policy-making and the knowledge economy.

Teachers and Pupils:
At CCSP, teachers and scientists interact during workshops and training and discussion days focussed on transferring knowledge on key topics relating to climate change. The impact of this proposal will be delivered in a series of CCSP workshops and by the development of an online learning tool. Activities will be aimed at increasing awareness of what controls ice stability, what the impacts of changing ice behavior are, and how we go about understanding these impacts. The aim is to directly benefit local teachers, and thereby their students, within the timeframe of this project. Wider schools impact will continue to expand year-on-year beyond the end of the project as the outcome of this work is integrated into the CCSP programme of teaching. The twin approach of teacher discussion/training and the development and use of an online learning support tool will engage students and teachers in discussion of the controls on ice behavior and the use of 'models' to 'predict' the future.

Policy and Economy:
The direct economic impact for the UK is difficult to assess, but this work will strengthen the UK scientific and knowledge economies by providing the basis for future research with respect to predicting future earth system behavior as the result of climate change. Governments are becoming increasingly aware that by early investment in policy developed through an understanding of the risks associated with climate change, a financial benefit may be felt in the longer-term. There will therefore be a global economic benefit in the medium to long term, contributing to the 'green economy' and to policy developments. It is anticipated that the impact in this area will be delivered via submissions to lead authors on the international framework for advising governments on environmental policy - the Intergovernmental Panel on Climate Change (IPCC). The economic impact will be delivered on a timeframe longer than this project and the potential for impact is significantly increased by interaction with the IPCC. It is envisaged that the route for interaction with the IPCC will be facilitated via contributions to the Scientific Committee on Antarctic Research (SCAR) to which the PI has previously contributed. SCAR produces advisory reports that are fed into the IPCC process, and to governmental policy development of SCAR member nations.

Knowledge Economy:
UK universities and international institutions will benefit by the development of a new numerical model that enables the systematic investigation of interactions between glaciology, bed evolution, sea level and climate change. This technological advance will bring impact that can be felt more widely, and over a longer time period, through the distribution of the model to other UK and international academic users. The 'knowledge economy' will also benefit by the national and international links fostered in this project in pursuit of understanding of a recently identified feedback in the cryosphere. There is prestige for the UK associated with leading this programme of research.