A numerical study of the climate response to lowered Mediterranean Sea level during the Messinian Salinity Crisis

Abstract

Roughly six million years ago, tectonic movements isolated the Mediterranean Sea (MS) from the Atlantic Ocean, an event known as the Messinian Salinity Crisis (MSC). Subsequent evaporative drawdown of the MS resulted in a subaerial depression with a depth between 1500 and 2500 m. In this study, five simulations are run using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 3 (CAM3) configured with the slab ocean model. Three simulations have been performed to test the climate impacts to desiccation and to changing the MS base level. In this study, the MS base level is reduced 750 m in the Half Land simulation (HL), and 1500 m in the Lowered Sea (LS) and Lowered Land (LL) simulations. The HL and LL simulations differ from the LS in that the surface is converted to land, representing the complete desiccation of the MS. The substantial MS depression generates planetary-scale atmospheric waves responsible for significant climate effects throughout the Northern Hemisphere. A notable deepening of the Aleutian Low and a significant equatorward shift in the Atlantic jet stream are evident. In DJF, vertical ascent at the northern margin of the MS results in a 1.5–2.5 mm day − 1 precipitation anomaly in the LS run over the Alps, consistent with proxy data. Annual mean area averaged MS evaporation is slightly higher than control conditions. Except when salinity is a substantial barrier to evaporation, our results suggest that a partially filled basin cannot exist in equilibrium and the MS must either be partly connected to the Atlantic Ocean or completely desiccated. Base level lowering, which alters the water budget, must be taken into account when considering the freshwater budget during the MSC.