Ice blocks melting into a salinity gradient

Abstract

I n our previous qualitative paper, it was shown that when a vertical ice surface melts into a stable salinity gradient, the melt water spreads out into the interior in a series of nearly horizontal layers. The experiments reported here are aimed a t quantifying this effect, which could be of some importance in the application to melting icebergs. Experiments have also been carried out with heated and cooled vertical walls a t larger Rayleigh numbers R than those of previous experiments.The main result is that for most of our experiments there is no significant difference between these three cases when properly scaled. The layer thickness over a wide range of R is described to within the experimental accuracy by where the term in brackets is the horizontal buoyancy difference evaluated a t the mean salinity and dpldz is the vertical density gradient due to salinity. I n the case of ice melting into warm water the effective wall temperature T, is approximately 0 "C, whereas in colder water the freezing point depression must be taken explicitly into account. A detailed examination of the vertically flowing inner melt water layer in both homogeneous and salinity stratified cases has been made. This layer and the melt water which is mixed outwards from it into the turbulent horizontal layers have little effect on the outer flow. At high R and large external salinity, however, mixing can reduce the effective salinity a t the inner edge of the horizontal layers, and thus the layer scale. A puzzling feature is the relatively weak dependence of layer scale on local salinity, though the vigour of convection and the rate of melting are greater where the salinity is high.The direct application of our results to oceanographic situations predicts layer scales under typical summer conditions of order tens of metres in the Antarctic and of order metres in the Arctic. More measurements will be needed, especially close to icebergs, before the application of these ideas to polar regions can be properly evaluated.

The stratified Boycott effect

“…After the layering has evolved for a sufficient time, the density within a layer becomes uniform and tilting is no longer apparent (figure 7c). Note that this mechanism for tilting is distinct from that observed in thermohaline systems (Huppert & Turner 1980).…”

Rates and Mechanisms of Iceberg Ablation in the D’Urville Sea, Southern Ocean

“…Submarine ablation acts over the largest part of an iceberg and is believed to occur mainly by melting adjacent to a generally turbulent, convecting boundary layer (Huppert and Turner, 1980;Josberger and Martin, 1981). Water currents, iceberg wallowing, and roll -over enhanc e this melting by causing turbulent forced-convection (Job, 1978 ) .…”

“…Figure 2B illustrates the diluting effect, measurable on all four sides, of the iceberg, Keys and WiLLiams : I ceberg abLation obtained using a Yeokal Hamon S-T bridge. Fresh water is not found beside icebergs because the melt water produced at the ice face is mixed with surroundin g sea-water in a generally turbulent convecting boundary layer (Huppert and Turner, 1980;Josberger and Martin, 1981) . S-T depth profiles were made but usable results were not obtained at the positions shown on Figure 2A.…”

Supercooling of Seawater Near the Glacier Front in a Fjord

“…Foldvik and Kvinge (1974) considered a thermohaline convection of conditional instability in the ocean near the ice shelf released by the formation of ice crystals in the ascending water. A paper by Huppert and Turner (1980) considers a laboratory experiment when water originating from ice melting in stratified fluid forms a step structure. A similar structure is formed when water with a vertical gradient of salinity is cooled at a vertical wall.…”