Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica, and Jakobshavn Isbrae, Greenland

Abstract

Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

Instability of the Antarctic Ross Sea Embayment as climate warms

“…An answer to this question centers around solutions of the Navier‐Stokes equations. In one dimension along the direction of ice flow, a geometrical solution to these equations exists for sheet, stream, and shelf flow [ Hughes , , Equation (12.10) and Table 12.1; Hughes et al ., ]. In the geometrical force balance in horizontal direction x of ice flow, resistance to gravitational forcing is the sum of resistance from floating fraction ϕ of ice and grounded fraction 1 − ϕ of ice, where ϕ = 0 for sheet flow, 0 < ϕ < 1 for stream flow, and ϕ = 1 for shelf flow.…”

“…Ice‐bed coupling of Byrd Glacier was subsequently modeled excluding [ Reusch and Hughes , ] and including [ Hughes et al ., ] side drag. More recent modeling based on radar‐mapped bed topography directly compares basal drag with side drag [ Van der Veen et al ., ; Hughes et al ., ]. Both studies require basal sliding and weakened ice‐bed coupling.…”