Description: This project explores grain-scale signatures of subglacial sediment transport and subglacial hydrologic processes using grain shape and microtexture. We compare grain-shape distributions for grains from meltwater plume deposits to those of subglacial till and ice-proximal diamicton from the same glacial setting. The study incorporates samples from marine sediment cores collected offshore of Ryder Glacier in northwest Greenland, in the central Barents Sea, and Antarctic samples from Marguerite Bay, offshore Thwaites and Pine Island glaciers, and in the western Ross Sea. This dataset contains a MATLAB script used to process grain images and calculate individual grain-shape metrics (including circularity, solidity, and eccentricity), and an Excel spreadsheet containing the grain-shape measurements. Grain images were collected in 2022-23 using a Bettersizer S3 Plus particle size and shape analyzer at the University of Virginia.

Description: Ice streams dominate the discharge of continental ice sheets. Recent observations and reconstructions have revealed that large-scale reorganizations in their flow trajectory (flow switching) can occur over relatively short time scales. However, the underlying causes of such behavior, and the extent to which they are predictable, are poorly known. This paper documents a major episode of ice-stream flow switching during the late Weichselian deglaciation of the southwestern Barents Sea and explores various hypotheses for its causation. Regional bathymetric data show that two ice streams that had similar, adjoining, topographically constrained source areas had very different trajectories and dynamics on the outer shelf. At the late Weichselian maximum, the Håkjerringdjupet ice stream flowed westward along the cross-shelf trough of Håkjerringdjupet, while the Sørøya Trough ice stream flowed northward into Ingøydjupet, forming a tributary of the Bjørnøyrenna ice stream. Initial retreat of the Håkjerringdjupet ice stream was rapid but with episodic periods of grounding. As it retreated onto the higher, rougher topography of the inner shelf, we infer a reduction in ice velocity and a dramatic decrease in the pace of retreat, as recorded by nested sequences of recessional moraines. Following (and probably in response to) this, we suggest that there was a short-lived surge/readvance of an adjacent lobe onto Fugløybanken. In contrast, the adjacent Sørøya Trough ice stream remained active throughout deglaciation, before retreating rapidly, with no stillstands or readvances. We argue that the different retreat histories of the ice streams were determined by variations in bed topography/bathymetry, which modulated the grounding line response to sea-level variation. Such a mechanism is likely to be an important control on the long-term behavior of marine-based ice streams and outlet glaciers in Antarctica and Greenland and suggests that gathering data on their subglacial topography should be a priority.

Description: As ice flows over a subglacial lake, the drop in bed resistance leads to an increase in ice velocity and a subsequent lowering of the ice surface in the vicinity of the upstream lake edge. Conversely, at the downstream end of the lake a small hump is observed as the ice velocity decreases near the point of contact with land. There are two contributions arising from the ice/lake interaction: (1) changes in the thermal regime that propagate downwards with the advection of ice and (2) the increase in flow speeds caused by basal sliding over the lake surface. Sediment transport from upstream areas into subglacial lakes changes their size, thus reducing the area of the ice/lake interface. Here, we aim to study the effect that this reduction in size has on the flow dynamics and the surface elevation of an artificial ice stream and the temporal evolution of this effect. To this end, we use a full-Stokes, polythermal ice flow model, implemented into the commercial finite element software COMSOL Multiphysics. An enthalpy gradient method is used in order to account for the evolution of temperature and water content within the ice. This conceptual model uses prescribed boundary velocity and temperature profiles and a Weertman-type sliding law with a fixed parameter combination. In order to separate the effect of the slow thermal contribution from the fast mechanical one, we will present sensitivity tests that additionally involve a thermally-constant flow.