A box model of the blocked-outflow scenario for the Messinian Salinity Crisis

Part of the kilometre-thick Messinian evaporites of the Mediterranean basin is thought to have formed in a configuration of continuous inflow of water and salt from the Atlantic Ocean, in combination with blocked return flow. This mechanism is here examined for the first time quantitatively using a simple box model with parametrised exchange between sub-basins and including a representation of mixing. We also explore systematically the conditions under which the blocked-outflow state arises. The main results are (1) the rate of salinity increase is fast, (2) the western and eastern sub-basin evolve in concert except when exchange at the connecting strait is greatly reduced and then only when the basins are poorly stratified, and (3) near complete separation from the Atlantic is required to reach saturation unless Mediterranean waters are strongly stratified.