Ice stream formation

TL;DR

This paper models the spontaneous formation of ice streams in ice sheets through thermomechanical feedbacks, revealing how basal conditions and advection influence pattern development and stability.

Contribution

It introduces a novel thermomechanical model that captures lateral physics and explains ice stream formation via feedback amplification of basal noise.

Findings

Ice streams form from noisy basal conditions amplified downstream.

Downward advection of cold ice stabilizes the pattern.

Analytical criterion for pattern formation is provided.

Abstract

Ice streams are bands of fast-flowing ice in ice sheets. We investigate their formation as an example of spontaneous pattern formation, based on positive feedbacks between dissipation and basal sliding. Our focus is on temperature-dependent subtemperate sliding, where faster sliding leads to enhanced dissipation and hence warmer temperatures, weakening the bed further, although we also treat a hydromechanical feedback mechanism that operates on fully molten beds. We develop a novel thermomechanical model capturing ice-thickness scale physics in the lateral direction while assuming the the flow is shallow in the main downstream direction. Using that model, we show that formation of a steady-in-time pattern can occur by the amplification in the downstream direction of noisy basal conditions, and often leads to the establishment of a clearly-defined ice stream separated from slowly-flowing, cold-based ice ridges by narrow shear margins, with the ice stream widening in the downstream direction. We are able to show that downward advection of cold ice is the primary stabilizing mechanism, and give an approximate, analytical criterion for pattern formation.