UC Irvine

Petermann Glacier is a major outlet glacier of northern Greenland that drains a marine-based basin vulnerable to destabilization from enhanced oceanic and atmospheric forcings. Satellite observations show significant grounding line retreat of ∼7 km in a central region of the glacier, with at least 1 km of retreat elsewhere along the grounding line. This representsa significant shift from the glacier’s previously stable grounding line position mapped in the 1990s. Satellite observations also show a seasonal ice acceleration for Petermann of 15% in the summer, from 1,250 to 1,500 m/yr measured close to the grounding line. We use a subglacial hydrology model (GlaDS) and an ice sheet model (ISSM) with asynchronous coupling to evaluate the role of subglacial hydrology as a physical mechanism explaining the seasonal speedup of ice velocity. Results show an excellent agreement between the observed and modeled velocity in terms of timing and magnitude when an applied lower limit on effective pressure of 6% of ice overburden pressure is imposed in the ice flow model. We conclude that seasonal changes in subglacial hydrology are sufficient to explain the observed seasonal speed up of Petermann Glacier. Current projections of glacier dynamics under 21st century climate forcings do not include seasonality or subglacial hydrology, so it is unknown if either will play any important role in evolving glacier dynamics under different climate change scenarios. We use climate forcings through 2100 to investigate how the subglacial hydrologic system may evolve in a warmer climate, and to test if including hydrology changes the stability of Petermann under future climate scenarios using ISSM and the GlaDS model in both an asynchronous and synchronous coupled configuration. Results show that including subglacial hydrology in projections of Petermann’s evolution yield larger predictions of future sea level rise by the end of the century. However, modeled results of both present day and future ice dynamics with and without subglacial hydrology included do not reproduce the observed grounding line retreat. To better understand grounding line migration of Petermann, we apply a newly published theory of seawater intrusion below grounded ice. By incorporating ocean driven basal melting in the grounding zone, we achieve a significantly improved match to the observed grounding line behavior that previous model setups failed to reproduce. This underscores the importance of considering ocean-driven melting to accurately capture grounding line behavior. These studies contribute to a deeper understanding of the observed behavior of Petermann Glacier, particularly its seasonal acceleration and grounding line migration. Subglacial hydrology and seawater intrusion both emerge as influential short time scale processes on ice dynamics, with potential long term implications on glacier stability and sea level rise.