Reproducing seasonal patterns of surface velocity with a coupled ice flow and subglacial hydrology model

The evolution of the subglacial drainage system plays a key role in the seasonal behavior of ice surface velocities both on mountain glaciers and ice sheets. This relationship offers an opportunity to evaluate subglacial hydrology models against observations of large spatial and temporal coverage. Although surface velocities are only an indirect measure of the subglacial water pressure, and such a comparison therefore requires the coupling to an ice flow model through a sliding law, it presents a promising but currently still under-explored opportunity for the challenging task of constraining subglacial hydrology models.

In this study, we test a coupled ice flow and subglacial hydrology model in its ability to reproduce observed patterns of seasonal surface velocity on a group of land-terminating glaciers in southwest Greenland. These glaciers exhibit a variety of seasonal behaviors, including a spring acceleration with constant winter speed, a pronounced speed minimum in autumn, as well as a sustained speed-up throughout the winter. We use the Glacier drainage system model GlaDS, coupled to a higher-order ice flow model in a way that the whole system of equations is solved simultaneously, which allows an immediate two-way coupling. While the original GlaDS is restricted to constant winter water pressures (and velocities), we explore model extensions such as a laminar/turbulent transition that yield more complex seasonal behaviors. We investigate the interplay of the physical model choices, model parameters, properties of the bed topography, meltwater input and other factors to determine which conditions are necessary to produce certain types of seasonal behavior, and we evaluate if the observed patterns can be reproduced successfully in a realistic modeling framework.