Linked Cavities vs. Porous Media: Sensitivity of Ice Sheet Variability to Uncertain Subglacial Hydrology

Abstract:

The role of subglacial hydrology in ice sheet variability on glacial cycle time scales is relatively unknown. This understanding is complicated by the available structural choices in modelling the distributed component of subglacial hydrology. Two choices dominate published models: linked cavities and porous media, the contexts where each dominate is not well defined. Does this structural choice control ice dynamical behaviour at continental and glacial cycle scales? If so, how?

We analyze the role of subglacial hydrologic processes in periodic surge events over soft portions of the bed of an idealized Laurentide ice sheet. We use a fully coupled state of the art (for glacial cycle contexts) hydrology model, BrAHMs2.0, and the Glacial Systems Model (GSM). BrAHMs2.0 represents a trade off between complexity and large spatio-temporal scale: a parameterized choice of distributed drainage through poroelastic or linked-cavity systems with a flux based switch to tunnel drainage via a down gradient routing scheme. The GSM is a 3D thermomechanically coupled ice sheet model with hybrid shallow ice and shallow shelf physics. The analysis uses an ensemble based approach to determine the impact of parameter and structural uncertainty from the subglacial hydrology model. We illustrate in detail the impact of the choice of linked cavities versus porous media, given parameter uncertainties.