The model indicates that periodic tidal currents drive steady circulations having magnitude less than 0.02 m s−1 along the sides of several topographic bumps and ridges below the ice shelf. Ventilation of the sub-ice-shelf cavity is indicated by the Lagrangian trajectories shown in Figure 1. The cross ice-front heat transport resulting from this flow is estimated to induce approximately 0.5 ± 0.25 m a−1 basal melting over 10% of the ice-shelf area closest to the eastern and western ends of the ice front.
Fig. 1 Tracer streak-lines emitted from the ice front and select sub-ice-shelf locations display how tidal rectification ventilates the sub-ice-shelf cavity.
The observed rate of water mass renewal within the entire sub-ice-shelf region cannot be attributed to tidally driven barotropic circulation alone. Another circulation mechanism related to tidally induced vertical mixing may, however, operate in the deeper reaches of the sub-ice-shelf cavity. Away from the ice front, the warmest water resides at the sea bed because of its high salinity. Basal melting is thus suppressed unless turbulence generated by tidal currents is sufficiently strong to completely mix the water column against buoyancy input. From analysis of the budget produced by the numerical simulation, complete vertical mixing is anticipated in the shaded regions of Figure 2. These mixed zones are primarily along the Siple Coast where the watercolumn thickness is less than 100 m.
Fig. 2 Shaded regions indicate where tidal-energy dissipation is predicted to cause vertically wellmixed waters and thereby to induce strong basal meltin.
Basal melting in the well-mixed region is estimated to be between 0.05 and 0.5 m a−1, and will drive a thermohaline circulation having the following characteristics: warm high-salinity water formed in the open Ross Sea during winter flows along the sea bed towards the tidal-mixing fronts, vertical mixing behind the fronts promotes heat transfer between the water and ice, catalyzing basal melting, and meltwater produced behind the fronts flows out of the sub-ice-shelf cavity between the inflowing warm water and the ice-shelf base.
Given present conditions, basal melting along the well-mixed Siple Coast is not expected to be sensitive to climatic change because the inflowing water mass is constrained to have the sea-surface freezing temperature. For this buffering to be upset by climatic change, the production of high-salinity water on the continental shelves of Antarctica must be eliminated.
