Modelling the effect of evaporation on the salinity–87Sr/86Sr relationship in modern and ancient marginal-marine systems: the Mediterranean Messinian Salinity Crisis

Palaeosalinity reconstructions in marginal marine environments based on Sr isotope data assume simple two end-member mixing of river and ocean water. An improved model that incorporates the effect of evaporation is used to demonstrate that this approach is not valid in evaporation-dominated systems. However, Sr isotope records combined with faunal and lithological constraints on salinity can be used to assess the palaeohydrological conditions of ancient marginal marine systems. This new method is used to interpret deviations from the global seawater Sr isotope curve, observed in Mediterranean successions during, and up to 3 Myr prior to, Messinian evaporite deposition. Results suggest that no absolute change in the net evaporation flux is required to explain the three- to four-fold rise in salinity of Mediterranean water at the carbonate–evaporite transition. Modelled Sr isotope records indicate that this increase in salinity was synchronous with an increase in the dominance of Atlantic water inflow in the hydrological budget of the Mediterranean. The Messinian Salinity Crisis may therefore have been the response to a marine transgression.