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

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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.