A coupled heat and salt transport model for sub-sea permafrost

Abstract

The sub-sea permafrost regime off much of Alaska’s arctic coast can be understood by considering the response of land-formed permafrost to changing temperature and salinity conditions associated with shoreline recession. Sea-bed temperatures seem to be negative in much of the Beaufort Sea, but inundated permafrost will still thaw downward from the sea bed if the sea water is above its freezing temperature. The process cannot be understood within the framework of conventional heat transport models because of the key role played by salt. This is illustrated by a simple coupled heat and salt transport model, solved in closed form, in which heat and mass are transported by diffusion. The solution is a generalization of the Stefan solution for growth of an ice cover. It illustrates how the thawing rate depends almost entirely on salt transport properties at a sea-bed temperature of -1°C, on thermal properties at +1°C, and on both at intermediate temperatures. The calculated thawing rates are so slow in this diffusion model that the significance of pore liquid motion is suggested.