A new study published in Science Advances revisits one of the most extreme events in Earth’s geological history - the Messinian Salinity Crisis (MSC), when the Mediterranean Sea became almost entirely cut off from the Atlantic Ocean between 5.97 and 5.33 million years ago.
The crisis led to the precipitation of an estimated one million cubic kilometers of salt, reshaping marine ecosystems and trapping as much as 5% of the world’s ocean salt on the Mediterranean seafloor. Yet, the scale of water loss and refilling during the crisis has long been debated.
Using landscape evolution modeling, Daniel García-Castellanos and colleagues show that erosion of spillways from surrounding basins, including the Paratethys and Pannonian lakes, gradually fed freshwater into the Mediterranean, superimposed on orbitally driven climate oscillations. This process produced repeated and kilometer-scale sea-level changes - from nearly total desiccation to partial refilling with brackish water.
The findings help resolve a long-standing paradox in the geological record. Deep drilling projects revealed shallow-water fossils in sediments deposited more than two kilometers below present sea level, implying that brackish “Lago-Mare” conditions coexisted with extreme drawdowns. The new model explains this by showing that Mediterranean levels fluctuated widely within short geological timescales, alternating between near-empty basins and nearly full, freshwater-influenced lakes.
The study also suggests that erosional waves cutting through the Bosphorus and Aegean outlets progressively lowered the Paratethys lakes, transferring their water into the Mediterranean and raising its level by more than a kilometer toward the end of the crisis. These freshwater inflows explain the widespread Lago-Mare deposits found along Mediterranean margins.
Ultimately, the MSC ended with the catastrophic Zanclean flood 5.33 million years ago, when Atlantic waters reentered through the Strait of Gibraltar, refilling the basin in what may have been a matter of years.
According to the authors, these results not only clarify a “geological mystery” but also offer insights into how large basins respond to tectonic closure, climate cycles, and river erosion. The MSC remains a critical case study for understanding salt-giant formation and the survival of marine life under extreme environmental stress.
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