Abstract
Flow organization into systems of fast-moving ice streams is a well-known feature of ice sheets. Fast motion is frequently the result of sliding at the base of the ice sheet. Here, we consider how this basal sliding is first initiated as the result of changes in bed temperature. We show that an abrupt sliding onset at the melting point, with no sliding possible below that temperature, leads to rapid drawdown of cold ice and refreezing as the result of the increased temperature gradient within the ice, and demonstrate that this result holds regardless of the mechanical model used to describe the flow of ice. Using this as a motivation, we then consider the possibility of a region of 'subtemperate sliding' in which sliding at reduced velocities occurs in a narrow range of temperatures just below the melting point. We confirm that this prevents the rapid drawdown of ice and refreezing of the bed, and construct a simple numerical method for computing steady-state ice sheet profiles that include a subtemperate region. The stability of such an ice sheet is analysed in a companion paper.
Highlights
Sciences, University of British Columbia, Vancouver, CA ∗present address: AOS Program, Princeton University, Princeton (NJ), USA ∗∗present address: Department of Earth Sciences, University of Oxford, Oxford, UK
We show that an abrupt sliding onset at the melting point, with no sliding possible below that temperature, leads to rapid drawdown of cold ice and refreezing as the result of the increased temperature gradient within the ice, and demonstrate that this result holds regardless of the mechanical model used to describe the flow of ice
Using this as a motivation, we consider the possibility of a region of ‘subtemperate sliding’ in which sliding at reduced velocities occurs in a narrow range of temperatures just below the melting point
Summary
A discontinuous vertical velocity at the cold-temperate boundary is likely to have significant consequences for heat transport: a delta function in w suggests that streamlines should be discontinuous at x = xonset, and isotherms may be discontinuous when viewed at the ice sheet scale, precisely how is unclear. In reality, this appears to indicate the need for a boundary layer that resolves the ice thickness scale in the horizontal direction near the transition point.
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