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Cambridge NERC Doctoral Landscape Awards (Training Partnerships)

Graduate Research Opportunities
Brief summary: 
This project aims to assess the stability of Antarctic grounding zones – where the ice sheet meets the ocean and transitions to a floating ice shelf - by comparing simplified models of subglacial hydrology and sediment transport to modern and paleo-reconstructions of the grounding zone to assess future stability of the West Antarctic Ice Sheet.
Importance of the area of research concerned: 
Runaway loss of ice from the West Antarctic Ice Sheet (WAIS) is the biggest threat to sea level rise. Current loss of glacial ice is driven by changing oceanic conditions driving melting within the grounding zone of the floating ice shelves, thus reducing the buttressing stresses which modulate ice motion. These same stresses at the base of ice sheets, both in the grounding zone and at pinning points, mobilise and transport significant basal sediment leading to longer term variation in the basal topography of the grounding zone. Mobilised sediments in the grounding zone can produce transverse ridges in the sea floor, and have been used to infer rapid retreat of the grounding zone during the past regional deglaciation of the Larsen Ice Shelf. Sediments also build into large grounding zone wedges which may provide topographic pinning points, stabilising the grounding zone. Widespread retreat of the WAIS is known to have halted at these features for 100s-1000s of years during the last deglaciation. Understanding the redistribution of sediment in the grounding zone is therefore important to interpreting past grounding zone stability, predicting future sea level rise.
Project summary : 
This project will focus on the role of transient subglacial hydrology in the mobilisation of grounding zone sediment over a range of time scales using modern observational data and a hierarchy of simplified mathematical models. On tidal timescales water flows in the subglacial cavity and the subglacial hydrological network in the grounding zone. On longer timescales rerouting of the subglacial hydrological network alters the water pressure at the base of the ice. Both result in modulation of the basal traction between ice and sediments on timescales from the tidal modulation through to much longer seasonal and decadal variability. This project will simulate the flow of water in the grounding zone using hybrid laminar-turbulent formulations, and the redistribution of sediment to assess the temporal and spatial variability of basal traction and sediment redistribution.
What will the student do?: 
The student will be involved in developing a hierarchy of mathematical models of the grounding zone to examine the interplay between transient and long-term hydrological forcing and sediment redistribution. The student will predict flow in the grounding zone to understand the shear stresses on ice and sediment over tidal and longer timescales. These flows will be used to predict ice melt rates and to understand the transient water pressure within the grounding zone, and hence the basal traction and mobilisation of sediment. On longer timescales the coupling between spatially and temporally variable traction will also be used to understand the modulation of ice flow. These simplified models will be informed by, and compared with, modern observations from a suite of sites around the Antarctic, most prominently from the Institute Ice Stream (IIS) but also from the Larsen Ice Shelf and from Thwaites Glacier. A inter-comparison of geophysical settings will highlight differing oceanic forcings, pre-existing sedimentary architectures, and most importantly enable comparison with a wider range of geophysical and geological observations.
References - references should provide further reading about the project: 
Warburton, K. L. P., Hewitt, D. R. & Neufeld, J. A. Tidal Grounding‐Line Migration Modulated by Subglacial Hydrology. Geophys Res Lett 47, (2020).
Hogan, K. A. et al. Towards modelling of corrugation ridges at ice-sheet grounding lines. The Cryosphere Discuss. 2022, 1–29 (2022).
Warburton, K. L. P., Hewitt, D. R. & Neufeld, J. A. Shear dilation of subglacial till results in time-dependent sliding laws. Proc. R. Soc. A 479, 20220536 (2023).
You can find out about applying for this project on the Department of Applied Mathematics and Theoretical Physics (DAMTP) page.