C057-04
Melting at the Grounding Zone of Thwaites Glacier Observed by Icefin
Tuesday, 15 December 2020: 05:42
Virtual
Britney E Schmidt1, Peter Washam2, Peter E D Davis3, Keith W Nicholls3, Justin Lawrence2, James Smith3, Kiya L Riverman4, Daniel Dichek5, Andrew David Mullen2, David Holland6, Aurora Basinski-Ferris7, Paul Anker3, Matthew Ryan Meister2, Anthony Spears2, Ben Hurwitz2, Enrica Quartini2, Frances E Bryson2, Elisabeth Rose Clyne8, Catrin Thomas3, James Wake3, David Glyn Vaughan9, Sridhar Anandakrishnan10, John Drysdale Paden11, Eric J Rignot12, Benjamin Yeager6 and Keith Makinson13, (1)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (2)Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, GA, United States, (3)British Antarctic Survey, Cambridge, United Kingdom, (4)University of Oregon, Eugene, OR, United States, (5)Georgia Institute of Technology, Atlanta, GA, United States, (6)New York University, New York, NY, United States, (7)New York University, New York, United States, (8)Pennsylvania State University, University Park, United States, (9)NERC British Antarctic Survey, Cambridge, United Kingdom, (10)Pennsylvania State University, University Park, PA, United States, (11)University of Kansas, Lawrence, United States, (12)University of California Irvine, Department of Earth System Science, Irvine, CA, United States, (13)NERC British Antarctic Survey, Polar Oceans, Cambridge, United Kingdom
Abstract:
From January 9-12 2020, ROV Icefin conducted the first long range robotic exploration of the grounding zone of Thwaites Glacier, as part of the ITGC MELT project. Icefin, an underwater vehicle designed for borehole deployments, conducted 5 missions amassing over 15km of continuous data collection with oceanographic, imaging and sonar sensors. Missions extended seaward over 3.2km from the grounding zone, where Icefin observed ice-seafloor contact, traversing a <1 m water column. Imagery and sonar revealed diverse basal ice conditions and complex geometries, including terraced features, both smooth ablated and cuspate melted surfaces, crevasses, various sediment laden layers, and interspersed clear freshwater ice accreted upstream of the grounding zone. These offer a window into upstream hydrological and glaciological conditions. The water column ranges from ~100m thick downstream, thinning to ~50m, and quickly narrowing in the last ~500m towards the grounding zone. Ocean conditions vary from moderately well-mixed near the grounding zone to highly stratified near the ice base at seaward locations. Generally subdued seafloor topography is roughly parallel to ice flow. Sediments range from fine grained downstream to course angular gravel distributed between larger boulders near the grounding zone; and much of the basal ice contains heavy sediment load, often size sorted. We also catalogued organisms from the seafloor to the ice-ocean interface, including ice-burrowing anemones.
From the combined Icefin oceanographic and ice profiling data, the emerging perspective is that topography along the ice-ocean interface evolves dramatically from the grounding zone. Features such as terraces that have been commonly associated with subglacial meltwater channels are instead found across the basal ice surface of the whole survey area. This indicates that in warm oceanographic settings the lateral advection of heat into the ice drives faster melting than vertical melting, which is suppressed by stratification along the flat ice base. These observations demonstrate that the ice-ocean interface is complex at scales and geometries not commonly observed, and imply that the topography of the ice base influences mass loss from Thwaites Glacier.
