Impact of deep subglacial groundwater on ice stream flow in West Antarctica (IGIS)

Lead Research Organisation: Swansea University
Department Name: College of Science

Abstract

Our project will test the hypothesis that 'deep subglacial groundwater groundwater (contained within crustal basins of sedimentary rock) controls the flow of ice streams in West Antarctica' with an integrated programme of field measurements and numerical modelling of the Institute Ice Stream (IIS) and its cold-based neighbour the Bungenstock Ice Rise (BIR), in the central Weddell Sea sector of the West Antarctic Ice Sheet (WAIS). The IIS is particularly vulnerable to dynamic change and one of the largest sources of uncertainty in predictions of sea level change from Antarctica, and therefore an urgent priority for further scientific investigation.

Ice streams are the fast-flowing conduits of the WAIS that discharge some 90% of continental ice into the ocean, requiring a substrate of basal till that dilates because it is lubricated well by water. Till is commonly supplied by ice flow over highly erodible sedimentary rocks contained within crustal basins beneath ice streams in the WAIS, tens to thousands of metres deep. Till layers can deform, facilitating fast basal slip and ice streaming when subglacial hydrological sources drive in water that softens them. The opposite effect is observed when water outflow into hydrological sinks stiffens the till, reducing basal slip. Irrespective of how current numerical models parameterise basal slip, a misrecognition of spatial or temporal variability in water and heat sources or sinks will translate directly into incorrect simulations of such slip and therefore of ice stream flow.

The water is usually assumed to be produced and flow in a hydrological system at the ice-till interface, and the underlying sedimentary rocks to be impermeable. Evidence is now growing that this assumption is in fact wrong because these rocks can be more permeable than previously thought, and host to reservoirs of mobile groundwater that interacts hydrologically with the interfacial water system. Numerical model simulations of the WAIS's Siple Coast catchment, the East Antarctic Ice Sheet, the Vatnajökull Ice Cap in Iceland and the hydrological impacts of previous glaciations on contemporary groundwater reservoirs in sedimentary basins, all simulate vigorous transfers of water and heat between ice sheets and the underlying groundwater reservoirs.

A major source of water and heat available for basal lubrication may therefore have been overlooked in models of ice stream flow, and it is now urgent that our understanding of ice-stream - groundwater interactions is transformed.

We will identify the anatomy of the crustal groundwater reservoir beneath the IIS, the spatial and temporal nature of water and heat transfer between it and the interfacial water system, the inherent effects on the basal lubrication of the IIS, and quantify its vulnerability to future groundwater-modulated dynamic change. We will do this with a field data acquisiton programme that will deliver the essential datasets required to constrain numerical model simulations of groundwater-ice stream coupling. Seismic geophysical data will diagnose internal structures and bulk porosities of subglacial till and the groundwater reservoir in the sedimentary basin beneath the IIS - importantly bulk aquifer and aquitard layers as well as tunnel valleys - and delineate target subglacial lakes and any subglacial permafrost captured by the BIR profiles. MT data will delineate liquid groundwater within the reservoir structures and affirm the presence of any permafrost beneath the BIR.

If the hypothesis is confirmed then we will have (1) transformed our understanding of ice stream flow in the WAIS, (2) formed and disseminated the knowledge required to improve ice-sheet models and their simulations of future WAIS change, and (3) exemplified and shared this by embedding it within the community ice sheet model CISM-2.

Planned Impact

Who could potentially benefit from the proposed research over different timescales?

Our project will have research translation benefits to a wide-range of beneficiaries on immediate, intermediate and long-term timescales, as follows:

1. Our project, in terms of both the fieldwork and scientific findings, will be of interest to the public, for which there is a long-standing fascination for understanding the vast ice sheet of Antarctica and its exploration. Outreach to the public, from school children to adults, using our project to instil a greater awareness of the environment, will therefore be an important aspect of our impact strategy.

2. On intermediate timescales of a few years our project will be highly relevant to policy makers concerned with the response of the Antarctic Ice Sheet to climate forcing. Understanding how Antarctica is prone to change requires knowledge of the processes by which the ice flows. Experience informs us that fascination with Antarctic exploration in projects like ours, offers policy makers and influencers a means by which complex environmental issues can be comprehended. We will therefore use our blue skies research to this advantage, making it a gateway to matters relating to Antarctic change and sea-level rise.

3. On longer timescales of decades the Antarctic Ice Sheet is likely to continue to lose mass in certain places, contributing to further sea-level rise. Although not of direct and immediately obvious benefit, the new knowledge generated by our project will ultimately improve our ability to model ice sheet processes, and so enhance predictions of future ice sheet change, assisting the development of appropriate adaption measures against sea level rise.


How might the potential beneficiaries benefit?

Outreach and impact activities are an integral part of our project, and are aimed at reaching the three main groups of potential beneficiaries identified above. We summarise below activities to ensure benefit, which is explained in exhaustive detail in our Pathways to Impact document.

1. As explained in exhaustive detail in the Pathways to Impact, the public will benefit through focused outreach ventures such as 'Oriel Science' (http://orielscience.co.uk/), which is Swansea University's new Science Outreach and Public Engagement Centre, public-facing project website, Facebook page, regular blogs from the field, and a range of public science festivals.

2. It is important that policy makers are aware of the cutting-edge ideas in science (noting research in the IPCC is often several years old), and centres like the Grantham Institute at Imperial College, which Co-I Siegert co-directs, is ideally suited to undertaking such translation because it is 'supported by a team of experts who provide authoritative analysis and assessment of research outputs, communicating it in a policy-relevant way to decision makers'. This will be further enhanced through the project team's close association with the Scientific Committee on Antarctic Research (SCAR) that 'endeavours to make Antarctic science and policy work effectively to benefit society'.

3. Although not of direct and immediately obvious benefit, our project will also provide essential science that will underpin future adaptation measures against sea level rise. This is relevant because (i) more than 40% of the world's population lives within 150 km of the coast, and it is here where the rate of global population growth is greatest; (ii) the economic cost of sea level rise is estimated to run into the 10s of billions of US dollars globally; and (iii) the UK will be particularly affected, as an island with a coastline longer than 18,000 km.

4. If groundwater is revealed to be widespread in sedimentary reservoirs beneath the Antarctic ice sheet then it is likely also present beneath the Greenland Ice Sheet and smaller ice caps and glaciers, with scientific and policy implications akin to those that apply to Antarctica.

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