Modelling the Amery Ice Shelf

Abstract

The Amery Ice Shelf (AmIS), buttressing 16% of the grounded ice sheet in East Antarctica, contains deep ice reaching >2000 m below sea surface. This configuration makes the AIS susceptible to ocean changes. Although satellite observations have shown a relatively low melting of AmIS in recent decades, its fate in a warming climate remains uncertain. The aim of this thesis is to enhance our understanding of ocean-driven melting of AmIS and to explore potential future changes in the AmIS melting.

The first objective of this thesis is to investigate the long-term variability of basal melting beneath AmIS and oceanic processes that drive the AIS melting. A historical simulation over the period of 1976-2005 is conducted using a regional NEMO model. The variability of melt rates of AmIS is driven by the dominant water masses, modified Circumpolar Deep Water (mCDW) and Dense Shelf Water (DSW), in the sub-ice shelf cavity. For an mCDW-dominant AmIS cavity, which is controlled by a positive melt feedback loop, it has a residence time of ∼1.5 years. For an DSw-dominant AmIS cavity, it establishes a negative melt feedback loop, resulting in a residence time of 1-4 years. This implies that a warmer AmIS cavity is more susceptible to warming on the continental shelf, as it exchanges with the surrounding water faster, and it is more sensitive to the external forcing. The second objective of this thesis is to project the AIS melting by 2100 under different climate scenarios.

The melt rate is projected to increase from 0.7 m·yr⁻¹ to 8 m·yr⁻¹ in the low-emission scenario or 17 m·yr⁻¹ in the high-emission scenario in 2100. A tipping point of melt rate happens in the 2060s in both scenarios. A mechanism that drives the jump of melting is revealed. The changes in local salinity (and then density) form a new geostrophic balance, leading to the reversibility of local currents. This transforms the AmIS from a cold cavity to a warm cavity, and thereby triggering a tipping point of ice shelf melting. The projections suggest that a removal of the entire AmIS is likely to happen in the end of the 21st century under the high emission scenario. This implies that the future stability of AmIS in a warming climate is not robust as previously believed.

Date of Award	3 Oct 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Tony Payne (Supervisor), Christopher Bull (Supervisor) & William Seviour (Supervisor)