Dynamics of ice stream temporal variability: Modes, scales, and hysteresis

Abstract

Understanding the mechanisms governing temporal variability of ice stream flow remains one of the major barriers to developing accurate models of ice sheet dynamics and iceâ€climate interactions. Here we analyze a simple model of ice stream hydrology coupled to ice flow dynamics and including drainage and basal cooling processes. Analytic and numerical results from this model indicate that there are two major modes of ice stream behavior: steadyâ€streaming and bingeâ€purge variability. The steadyâ€streaming mode arises from frictionâ€stabilized subglacial meltwater production, which may also activate and interact with subglacial drainage. The bingeâ€purge mode arises from a sufficiently cold environment sustaining successive cycles of thinningâ€induced basal cooling and stagnation. Low prescribed temperature at the ice surface and weak geothermal heating typically lead to bingeâ€purge behavior, while warm ice surface temperature and strong geothermal heating will tend to produce steadyâ€streaming behavior. Model results indicate that modern Siple Coast ice streams reside in the bingeâ€purge parameter regime near a subcritical Hopf bifurcation to the steadyâ€streaming mode. Numerical experiments exhibit hysteresis in ice stream variability as the surface temperature is varied by several degrees. Our simple model simulates Heinrich eventâ€like variability in a hypothetical Hudson Strait ice stream including dynamically determined purge time scale, till freezing and basal cooling during the binge phase. These findings are an improvement on studies of both modern and paleoâ€ice stream variability and provide a framework for interpreting complex ice flow models. Key Points We find two modes of ice stream variability: steady-streaming and binge-purge There is hysteresis in ice stream variability Siple Coast ice streams are near an abrupt transition to steady-streaming ©2013. American Geophysical Union. All Rights Reserved.