NSFPLR-NERC: THwaites Offshore Research (THOR)

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There is a consensus that incursion of warm water across the continental shelf is the main driver of contemporary retreat of Thwaites Glacier, which presents the greatest risk of future rapid global sea-level rise. Uncertainty in model projections of the future of Thwaites Glacier can be significantly reduced by a range of investigations seaward of the current grounding line, including extracting a record of decadal to millennial variations in warm water incursion and the history of pre-satellite era grounding line migration, and constraining the bathymetric pathways that control the flow of warm water to the grounding line. Sedimentary records and glacial landforms preserved on the seafloor will allow reconstruction of changes in drivers and the glacier's response to them over a range of timescales, thus providing reference data that can be used to initiate and evaluate the reliability of models. Such data will also provide insights on the influence of poorly understood processes on marine ice sheet dynamics. The proposed project includes an integrated suite of marine and sub-ice shelf research activities aimed atestablishing boundary conditions seaward of the Thwaites Glacier grounding line, obtaining records of the external drivers of change, improving knowledge of processes leading to collapse of Thwaites Glacier, and determining the history of past change in grounding line migration and conditions at the glacier base. These objectives will be achieved through high-resolution geophysical surveys of the seafloor and analysis of sediments collected in sediment cores from the inner shelf seaward of the Thwaites Glacier grounding line using ship-based equipment, and also from beneath the ice shelf using a corer deployed through the ice shelf via hot water drill holes.This project will use a suite of marine geological and geophysical data from seaward of the modern grounding line, to derive records of drivers and pre-satellite era retreat history, and determine key boundary conditions that control Thwaites Glacier retreat. The data will be used to address three pairs of hypotheses about the behavior of Thwaites Glacier. The first pair of hypotheses address the impact of warm-water incursions on glacial stability, both the modern pathways for such incursions and the 20th century history of warm-water initiated retreats. The second pair of hypotheses address the role of subglacial meltwater on Thwaites Glacier stability, using a comparison of modern sediment flux rates to those recorded in cores to test the episodic nature of subglacial meltwater output, and of its influence on glacial stability. Finally, the third pair of hypotheses address the role the nature and topography of the bed and ice shelf pinning points have on stabilizing the grounding line.