The Messinian salinity crisis (MSC),
also referred to as the Messinian event,
and in its latest stage as the Lago Mare event,
was a geological event during which the Mediterranean Sea went into
a cycle of partial or nearly complete desiccation (drying-up)
throughout the latter part of the Messinian age of the Miocene epoch,
from 5.96 to 5.33 Ma (million years ago).
It ended with the Zanclean flood, when the Atlantic reclaimed the basin.
Sediment samples from below the deep seafloor of the Mediterranean Sea,
which include evaporite minerals, soils, and fossil plants,
show that the precursor of the Strait of Gibraltar closed tight about 5.96 million years ago,
sealing the Mediterranean off from the Atlantic.
This resulted in a period of partial desiccation of the Mediterranean Sea,
the first of several such periods during the late Miocene.
After the strait closed for the last time around 5.6 Ma,
the region's generally dry climate at the time
dried the Mediterranean basin out nearly completely within a thousand years.
This massive desiccation left a deep dry basin, reaching 3 to 5 km (1.9 to 3.1 mi) deep
below normal sea level, with a few hypersaline pockets similar to today's Dead Sea.
Then, around 5.5 Ma, less dry climatic conditions resulted in
the basin receiving more freshwater from rivers,
progressively filling and diluting the hypersaline lakes into
larger pockets of brackish water (much like today's Caspian Sea).
The Messinian salinity crisis ended with the Strait of Gibraltar finally reopening 5.33 Ma,
when the Atlantic rapidly filled up the Mediterranean basin in
what is known as the Zanclean flood.
Even today, the Mediterranean is considerably saltier than the North Atlantic,
owing to its near isolation by the Strait of Gibraltar and its high rate of evaporation.
If the Strait of Gibraltar closes again
(which is likely to happen in the near future in geological time),
the Mediterranean would mostly evaporate in about a thousand years,
after which continued northward movement of Africa may obliterate the Mediterranean altogether.
Only the inflow of Atlantic water maintains the present Mediterranean level.
When that was shut off sometime between 6.5 to 6 MYBP,
net evaporative loss set in at the rate of around 3,300 cubic kilometers yearly.
At that rate, the 3.7 million cubic kilometers of water in the basin
would dry up in scarcely more than a thousand years,
leaving an extensive layer of salt some tens of meters thick and raising global sea level
about 12 meters.