How dry was the Mediterranean during the Messinian salinity crisis?

Abstract

The Messinian salinity crisis (MSC; 5.97–5.33 Ma) is an enigmatic episode of paleoceanographic change, when kilometers-thick evaporite units were deposited in the Mediterranean basin. It is generally accepted that during the MSC interval there was a dry climate in the Mediterranean region. It is difficult to assess how dry the climate was during the MSC because a modern analogue, in size and duration, is absent. Here we reconstruct hydrological changes in the Mediterranean basin during the three main MSC stages using excellently preserved biomarkers. We used the hydrogen isotopic composition of the long chain n-alkanes (δDn-alkanes) to reconstruct the hydrological changes on the land adjacent to the Mediterranean Sea. Additionally, the δD of long-chain alkenones (δDalkenones) is used to observe changes in the Mediterranean Sea water source. The δDn-alkanes recorded during the deposition of Primary Lower Gypsum (stage 1) in Monte Tondo indicate a δD of the precipitation comparable to the present-day Mediterranean implying a similar hydrologic regime (indicated by experiments modelling the Miocene-Pliocene transition). Elevated δDalkenones values from halite unit (stage 2) of the Realmonte mine are associated with kainite and giant polygons, consistent with presumably high evaporative conditions during halite deposition. The δDn-alkanes recorded during the deposition of Upper Gypsum (stage 3) in Eraclea Minoa indicate a δDprecipitation typical for much drier settings, similar to the Red Sea region. The relative contribution of the different alkenones from Eraclea Minoa is similar to the one observed in present-day marine settings suggesting that, during stage 3, connections to the open Ocean were likely maintained. However, the δDalkenones records during deposition of the evaporites in Eraclea Minoa are similar to those synchronously registered in the Black Sea implying that a similar hydrologic regime, characterized by extended drought, covered large areas of southeastern Europe. Based on the δDalkenones similarity and the Paratethys type of ´Lago Mare´ fauna in the Mediterranean we speculate that the surface water during stage 3 was, at times, derived from the Black Sea.