Messinian salinity crisis regulated by competing tectonics and erosion at the Gibraltar arc

The persistent, shallow connection between the Atlantic Ocean and the Mediterranean Sea that caused the Messinian salinity crisis may have been sustained by a balance between tectonic uplift and erosion due to inflow. The Mediterranean's salinity crisis About six million years ago, a series of geological factors drastically reduced the exchange of water between the Atlantic Ocean to the Mediterranean Sea through what is now the Strait of Gibraltar. The resulting widespread salt precipitation in the Mediterranean, linked to a decrease in sea level of about 1.5 kilometres due to evaporation, is known as the Messinian salinity crisis. The exact mechanism that caused the crisis remains uncertain. Here Daniel Garcia-Castellanos and Antonio Villaseñor propose a competition between the obstruction of the Gibraltar arc seaway by tectonic uplift and its erosional deepening by water inflow, controlled by the resulting changes in sea-level difference across the Gibraltar arc, as a possible mechanism for the crisis. The Messinian salinity crisis 1 , 2 (5.96 to 5.33 million years ago) was caused by reduced water inflow from the Atlantic Ocean to the Mediterranean Sea resulting in widespread salt precipitation and a decrease in Mediterranean sea level of about 1.5 kilometres due to evaporation 3 . The reduced connectivity between the Atlantic and the Mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the Gibraltar arc seaway and global sea-level changes, both of which control the inflow of water required to compensate for the hydrological deficit of the Mediterranean 1 , 4 . However, the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the Mediterranean and the Atlantic 5 needed to explain the large amount of salt precipitated. Here we use numerical modelling to show that seaway erosion caused by the Atlantic inflow could sustain such a shallow connection between the Atlantic and the Mediterranean by counteracting tectonic uplift. The erosion and uplift rates required are consistent with previous mountain erosion studies, with the present altitude of marine sediments in the Gibraltar arc 6 , 7 and with geodynamic models suggesting a lithospheric slab tear underneath the region 8 , 9 , 10 . The moderate Mediterranean sea-level drawdown during the early stages of the Messinian salinity crisis 3 , 5 can be explain