Ice/hydrology feedback in the Siple Coast, Antarctica, from two-way coupled modeling

Abstract

Subglacial hydrological processes have long been understood to play a critical role in ice dynamics (Budd et al., 1979). Consequently, the recent emergence of complex two-dimensional subglacial hydrology models with both inefficient and efficient drainage components has led to two-way coupling of these complex hydrology models to ice flow models (Cook et al., 2022). Such two-way coupled models bring about questions regarding our implementation of friction in ice flow models and allow us to examine feedback mechanisms between the subglacial hydrological system and the ice sheet. This thesis investigates feedback mechanisms between the subglacial hydrological system and the ice sheet, and analyzes our current implementation of friction in ice flow models. This is accomplished through subglacial hydrology, ice flow, and coupled modeling of the Siple Coast of West Antarctica, which has a history of observable hydrology/ice flow feedback.

We use the Glacier Drainage System (Werder et al., 2013, GlaDS) model as a subglacial hydrology model, and the Shallow Shelf Approximation (Larour et al., 2012, SSA) with a mass transport model as an ice flow model, both of which are implemented in the Ice-Sheet and Sea-Level Systems Model (Larour et al., 2012, ISSM). We model the steady state subglacial hydrology of the Ross Sea subglacial hydrologic catchment, along with ice flow and two-way coupled ice flow/hydrology from 2010-2100 using an SSP585 surface mass balance forcing scenario. We test three different friction laws – the Budd friction law, the Schoof friction law, and a version of the Schoof friction law that we modify to ensure the sliding regime is representative of the cavitation at the glacier bed. Additionally, we test coupling with variable melt from frictional heating of ice, coupling with subglacial lake geometry altering glacier driving stress, and coupling with a combination of the two.

The effective pressure and the modeled sliding regime were found to be largely responsible for the evolution of fast flowing regions of the domain, highlighting the importance of two-way coupled models, which have a cavitation-dependent sliding regime. Feedback mechanisms between the subglacial hydrologic system and the ice sheet were identified, including a negative feedback mechanism that stabilized the basal shear stress and the effective pressure fields when variable melt was available to the subglacial hydrologic system. The inclusion of subglacial lake geometry on the glacier driving stress was found to have a large control on lake depth, with the potential for large speedup events corresponding to the fast filling of subglacial lakes. When all coupling components were active, a negative feedback mechanism between subglacial lake depth, glacier driving stress, and melt water production, which stabilized subglacial lake depth and ice motion was observed. The methods developed in this thesis and the limitations that we discovered for implementing subglacial processes in ice flow models will be highly valuable to the glaciological modeling community moving forwards.