A one-dimensional mixed layer model beneath the Ross Ice Shelf with tidally induced vertical mixing

Abstract

The dense High Salinity Shelf Water (HSSW) which spreads out below parts of the Ross Ice Shelf represents a heat-reservoir that can induce ablation if it comes into contact with the ice shelf base. One source of the mechanical energy necessary to lift the dense HSSW is small-scale turbulence induced by the shear of tidal currents at the sea-floor and at the ice shelf base. A one-dimensional Kraus-Turner-type model which is forced by a barotropic tidal current is coupled to the ice shelf by postulating that the ice-water interface is at the freezing point. The calculations indicate that the results of this two-layer approach allow a classification into a freezing and melting regime, depending strongly on the variability of the tidal currents with time and less on the intensity and the corresponding high production rate of turbulent kinetic energy. Based on an extended three-layer model ablation rates exceeding 0.4 m yr⁻¹ are obtained in the south-eastern part of the Ross Ice Shelf. Advection processes in the mixed layer directly beneath the ice shelf base are not considered. These results can therefore be regarded as indicating the maximum amount of ablation occuring in the deeper reaches of the ice shelf cavity. Application of the three-layer model to the J9-area in the central Ross Ice Shelf indicate a tidally induced vertical heat flux of 1.8 W m⁻² and a corresponding melting rate of 0.17 m yr⁻¹. As supported by ice core measurements, however, an accumulation rate of 0.03–0.05 m yr⁻¹ is estimated due to advection of freshwater produced immediately south of the J9-area.