Idealized Modeling Of Circulation Under Landfast Ice

Abstract

Idealized analytical and numerical models are used to elucidate the effects of a spatially variable landfast ice cover on under-ice circulation. Three separate forcing mechanisms are investigated; lateral inflow onto an ice-covered shelf (an elevated sea level at the western boundary), a spatially uniform upwelling wind blowing along the seaward landfast ice edge and a buoyant inflow under the ice cover that enters the domain through the southern coastal wall. The idealized models are configured to resemble the shallow Alaskan Beaufort Sea shelf. Models show that the inclusion of landfast ice means shelf response is substantially different from an ice-free shelf. In the case of a lateral inflow, landfast ice spreads the inflow offshore (in a manner similar to bottom friction) but the change in surface stress across the ice edge (from ice-covered to ice-free) limits the offshore spreading. In the case of an upwelling wind along the ice edge, the low sea level at the ice edge (due to ice edge upwelling) leads to a cross-shore sea level slope between the coast (high sea level) and the ice edge (low sea level), which drives a geostrophically balanced flow upwind. In the absence of along-shore changes in wind or ice the circulation does not vary along the shelf and currents near the coast are O(10 -3) m s-1. Along- and cross-shore variations in the ice-ocean friction coefficient introduce differences in the response time of the under-ice flow and can lead to along-shore sea level slopes, which drive along-shore flows near the coast (< 0.06 m s-1). In the case of a time dependent buoyant inflow, the landfast ice spreads the buoyant inflow much farther offshore (~ 9 times the local baroclinic Rossby radius, ~ 45 km) than in the ice-free case (< 30 km). When the ice width is finite, the change in surface across the ice edge acts to restrict offshore flow (in the anti-cyclonic bulge) and inhibits onshore flow farther downstream.