Natural desalination and equilibrium salinity profile of perennial sea ice

Abstract

Owing to the great local and temporal scatter of ice salinity, the shape of its steady-state profile in ice of equilibrium thickness is only approximately known. Hence the purpose of theorizing on the way in which it establishes itself is to suggest pertinent experiments rather than to explain physical causes. Four mechanisms of salt migration are discussed: (1) ‘Brine pocket diffusion’ as explained by W. G. Whitman; it is too slow to be of significance here. (2) ‘Gravity drainage,’ as observed in the laboratory by W. D. Kingery and W. H. Goodnow. It is unlikely to occur in natural, thick floating ice. Their basic concept may, however, be applicable in a modified form as a ‘flushing’ mechanism. (3) ‘Flushing’ or washing-out, a quantitative calculation that assumes the replacement of brine by meltwater from the surface to be a function of ice salinity and maximum temperature, leads to a steady-state salinity profile similar to that suggested by observations. (4) ‘Brine expulsion,’ as a result of temperature changes and the separation of liquid and gaseous inclusions during the cooling cycle is also treated numerically and results, as does (3), in a steady-state salinity profile resemblant of observations.