The HUB and Bathymetric Control Of Warm Water Inflow To Antarctic Ice Shelf Grounding Lines

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• Garrett Finucane, UCLA
• Wednesday 05 April 2023, 15:00-16:00
• BAS Seminar Room 1; https://ukri.zoom.us/j/96200879096.

If you have a question about this talk, please contact Dr Michael Haigh.

Across Antarctica ice shelves are losing mass at drastically different rates. Estimates suggest 55% of this ablation is due to basal melting within the ice shelf cavity, most of this by relatively warm Circumpolar Deep Water (CDW). Previous studies have suggested that the elevation of CDW is of primary importance in determining the heat transport into ice shelf cavities, and that the CDW temperature maximum has been shallowing in recent decades. However a general understanding of the relationship between the geometry of an ice shelf cavity, the offshore properties of CDW , and ice shelf melt remains lacking. In this study we investigate these relationships using MITgcm simulations of oceanic melt in an idealized ice shelf cavity geometry, and using observed melt rates beneath Antarctica’s ice shelves.

To the extent that CDW inflow is buoyancy-driven, it should be driven by the horizontal baroclinic pressure gradient, which is related to by the elevation of the CDW layer relative to an ice shelf’s bathymetry. To quantify the extent to which bathymetry obstructs CDW access to geometrically complex ice shelf cavities, we present a metric called the Highest Unconnected isoBath (HUB) that captures the elevation that CDW must reach before it may be expected to access the grounding line and induce melt. We find that the elevation of offshore CDW relative to the HUB closely predicts the melt rate across a suite of simulations with a wide range of quasi-randomized geometries. Computing this metric using observed Antarctic bathymetry and hydrography similarly explains much of the variance in the observed melt rates of Antarctic ice shelves, with various deviations that likely result from observational uncertainties and local influences of wind and buoyancy forcing over the continental shelf. These findings provide a generalized theoretical grounding for melt resulting from buoyancy-driven CDW access to Antarctic ice shelf cavities.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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