Sill-Controlled Circulation in Ice Shelf Cavities

Recent observations have revealed a topographic sill beneath the Pine Island Glacier in West Antarctica, and suggest that such features may be common in retreating ice shelves. The sill appears to modulate the inflow of warm Circumpolar Deep Water into the sub-ice shelf cavity, and thereby exert control over the ice melt rate. However, the extent of the sill control on the sub-shelf flow remains poorly understood. Observations inside ice shelf cavities are extremely sparse, and comprehensive ocean models have thus far provided limited insight into the dynamics of these sub-shelf flows. 

To explore the dynamics of these flows, we analytically model the problem as a hydraulically controlled two-layer exchange problem. The simplifying assumption of uniform potential vorticity is used to make such solutions tractable. We additionally present numerical integrations of a two-layer shallow water model with a rigid lid. We study the lateral boundary layer behavior in a lock-exchange setup and compare the results against our analytical predictions. In a parameter regime relevant to the Pine Island Glacier cavity, we find that the uniform-PV assumption is only valid within lateral boundary layers, and does not describe recirculatory flows occurring in the interior over the sill.