The spreading of a buoyant river plume beneath a landfast ice cover

A set of simple numerical model experiments are used to examine how river plumes spread beneath the landfast ice cover over a continental shelf. The model is configured to resemble the seasonally frozen Colville River which flows onto the Alaskan Beaufort Shelf. We compare three cases: no ice, a landfast ice cover that extends 25 km and 100 km offshore. In the absence of ice a strongly stratified plume forms and transports river water eastward in a narrow (20 km wide) coastal current. For the 25 km wide ice cover, the stratified plume spreads offshore (and slowly eastward) until it crosses the ice edge. At the ice edge, the plume forms a narrow (~10 km) along-ice jet that flows swiftly eastward, seaward of the ice-edge. For the 100 km wide ice cover (ice covering the entire model domain), the river influence extends 60 km from the coast and eastward flow is very weak everywhere. The difference among model runs is due to ice-ocean friction. When landfast ice is present, surface stress diverts the plume offshore in a frictional boundary layer. The plume continues to spread until the surface stress is relieved (at the ice edge). Although idealized, our results suggest that the spreading of buoyant plumes on arctic shelves differs markedly from those on ice-free shelves. The presence/absence of landfast ice will affect the fate of terrigenous sediments, and velocity and property distributions across the shelf. Hence lessons learned from mid-latitude buoyant plumes may not be transferable to landfast ice-covered shelves.