The role of sliding in ice stream formation

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, weak- ening the bed further, and on a similar feedback driven by basal melt water production. Using a novel thermomechanical model, we show that formation of a steady pattern of fast and slow flow can occur through the downstream amplification of noise in basal conditions. This process can lead to the establishment of a clearly defined ice stream separated from slowly flowing, cold-based ice ridges by narrow shear margins. Our model is also able to predict the downstream widening of ice streams due to dissipation and heat transport in these margins. We also show that downward advection of cold ice induced by accelerated sliding is the primary stabilizing mechanism that can suppress ice steam formation altogether, and give an approximate, analytical criterion for pattern formation.

Ice mass loss sensitivity to the Antarctic ice sheet basal thermal state

“…Our simulations do not show refreezing in thawable areas, which suggests that they could remain thawed after their initial frozen-to-thawed transition (Supplementary Note 4 ). However, as discussed above, the advances in ice mechanics and sliding onset physics for continent-scale ice sheet simulation codes are needed to examine the self-reinforcing feedbacks that could either lead to the ice thinning and eventually result in refreezing to the bed or permit sustained thawed conditions if frictional heating is great enough 21 , 22 .…”

“…External atmospheric and oceanic forcing can drive thinning and recession of ice shelves, reduce buttressing, and accelerate upstream ice 14 – 17 , which could alter the grounded ice basal thermal state as it adjusts to these environmental changes. Additionally, internal ice thermo-frictional feedbacks could create instabilities causing frozen-bed regions within a few degrees below the PMP to spontaneously thaw 18 – 21 . In these subfreezing regions (i.e., frozen areas with basal temperatures near the PMP), self-reinforcing feedbacks 22 mediated by temperature-dependent sliding 23 could lead to the spontaneous onset of wet-bedded, fast flowing ice and the emergence of ice streams 21 .…”

“…Additionally, internal ice thermo-frictional feedbacks could create instabilities causing frozen-bed regions within a few degrees below the PMP to spontaneously thaw 18 – 21 . In these subfreezing regions (i.e., frozen areas with basal temperatures near the PMP), self-reinforcing feedbacks 22 mediated by temperature-dependent sliding 23 could lead to the spontaneous onset of wet-bedded, fast flowing ice and the emergence of ice streams 21 . However, the effect of changes in the basal thermal state has not been constrained by observations or modeling 24 , 25 , so the impact on the dynamics and stability of the Antarctic Ice Sheet remains unknown.…”

Lubricated viscous gravity currents of power-law fluids. Part 2. Stability analysis

“…Weertman 1957;Nye 1969;Kamb 1970;Engelhardt et al 1990). These form fast-flowing ice streams, which are much more lubricated from below than the surrounding ice, as a result of increased basal sliding, a thermoviscous instability, or other flow instabilities (Hindmarsh 2004(Hindmarsh , 2009Sayag & Tziperman 2008;Kyrke-Smith, Katz & Fowler 2014, 2015Hewitt & Schoof 2017;Schoof & Mantelli 2021). Instabilities on the opposite end of the spectrum, involving thin films of fluid forming a more viscous crust over the main current, are relevant to cooling lava domes, forming a solidifying crust (Fink & Griffiths 1990Stasiuk, Jaupart & Sparks 1993;Balmforth & Craster 2000).…”

Inferred basal friction and mass flux affected by crystal-orientation fabrics

“…Basal drag provides an important resistive component in the force budget of glaciers and ice sheets, with implications for the accuracy of mass-loss projections and the dynamics of ice streams (Echelmeyer and others, 1994; Gillet-Chaulet and others, 2012; Larour and others, 2012; Morlighem and others, 2013; Schoof and Mantelli, 2021). Basal drag is classically represented in the form of a sliding law following Weertman (1957), which relates the ice–bed sliding velocity to the resulting basal drag (synonymous with basal shear stress or basal traction) through a power law with an unknown friction coefficient and exponent.…”