Preprints
https://doi.org/10.5194/egusphere-2024-4058
https://doi.org/10.5194/egusphere-2024-4058
27 Jan 2025
 | 27 Jan 2025
Status: this preprint is open for discussion and under review for The Cryosphere (TC).

Sub-shelf melt pattern and ice sheet mass loss governed by meltwater flow below ice shelves

Franka Jesse, Erwin Lambert, and Roderik S. W. van de Wal

Abstract. Ocean-induced sub-shelf melt is one of the main drivers of Antarctic mass loss. Capturing it in ice sheet models is typically done by using parameterisations that compute sub-shelf melt rates based on local thermal forcing. However, these parameterisations do not resolve the 2D horizontal flow of the meltwater layer, either neglecting it entirely or simplifying its representation. In this study, we present a coupled setup between the ice sheet model IMAU-ICE and the sub-shelf melt model LADDIE. LADDIE resolves 2D horizontal meltwater flow beneath an ice shelf, incorporating both topographic steering and Coriolis deflection of meltwater plumes. We conduct simulations in a framework closely resembling the Marine Ice Sheet Model Intercomparison Project third phase (MISMIP+), which represents an idealised ice sheet-shelf system. Simulations using LADDIE to calculate melt rates reveal key differences compared to simulations using the widely adopted sub-shelf melt parameterisations. These differences primarily emerge as variations in timing, location, and persistence of strong melting, leading to distinct transient volume loss. In the LADDIE experiments, a stepwise increase in ocean temperatures induces an initial steepening of the ice draft near the grounding line. This strengthens the westward flow, which converges into a western boundary channel, leading to persistent strong melting along the western margin. Consequently, western margin thinning results in reduced buttressing and strong volume loss over the first period of the simulations. Over longer timescales, a weakened meltwater flow circulation due to reduced thermal forcing at the grounding line allows the western margin to thicken again, suppressing volume loss. In contrast, the parameterisation's limitations in representing the 2D horizontal meltwater flow prevent these experiments from capturing the influence of ice draft steepening on enhanced margin melt. This results in a different transient volume loss compared to LADDIE. The parameterisations either inherently overestimate the persistence of margin thinning, leading to a sustained strong volume loss, or they underestimate margin thinning, delaying the onset of strong volume loss. Our findings suggest that incorporating the more detailed melt patterns resulting from the 2D horizontal meltwater flow in ice sheet models could significantly alter projections of Antarctic ice sheet evolution compared to melt patterns computed by the currently more common parameterisations.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
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Franka Jesse, Erwin Lambert, and Roderik S. W. van de Wal

Status: open (until 10 Mar 2025)

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Franka Jesse, Erwin Lambert, and Roderik S. W. van de Wal

Data sets

Model output experiments F. Jesse https://doi.org/10.5281/zenodo.14526103

Model code and software

Source code IMAU-ICE and LADDIE F. Jesse https://doi.org/10.5281/zenodo.14526103

Video supplement

Animations Fig. 04 and Fig.06 F. Jesse https://github.com/FrankaJes/meltwater_flow

Franka Jesse, Erwin Lambert, and Roderik S. W. van de Wal

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Short summary
We introduce the coupling of a sub-shelf melt model with an ice sheet model to explore how horizontal meltwater flow below ice shelves affects ice sheet mass loss over time. We show that accurately modelling the meltwater flow direction leads to distinct feedbacks and transient volume loss, not captured by melt parameterisations that simplify flow direction. Our results highlight the importance of refining the meltwater flow representation in ice sheet models to improve sea level projections.
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