Adaptation of an Isopycnic Coordinate Ocean Model for the Study of Circulation beneath Ice Shelves

Abstract

Much of the Antarctic coastline comprises large, floating ice shelves, beneath which waters from the open ocean circulate. The interaction of the seawater with the base of these ice shelves has a bearing both on the rate at which Antarctic Bottom Water is formed and on the mass balance of the ice sheet. An isopycnic coordinate ocean general circulation model has been modified so as to allow the incorporation of a floating ice shelf as an upper boundary to the model domain. The modified code admits the introduction of an arbitrary surface pressure field and includes new algorithms for the diagnosis of entrainment into, and detrainment from, the surface mixed layer. Special care is needed in handling the cases where the mixed layer, and isopycnic interior layers, interact with surface and basal topography. The modified model is described in detail and then applied to an idealized ice shelf?ocean geometry. Simple tests with zero surface buoyancy forcing indicate that the introduction of the static surface pressure induces an insignificant motion in the underlying water. With nonzero surface buoyancy forcing the model produces a cyclonic circulation beneath the ice shelf. Outflow along the ice shelf base, driven by melting of the thickest ice, is balanced by deep inflow. The abrupt change in water column thickness at the ice shelf front does not form a barrier to buoyancy-driven circulation across the front.