Messinian salinity crisis

Artistic interpretation of the Mediterranean geography during its evaporative drawdown, after complete disconnection from the Atlantic. The rivers carved deep gorges in the exposed continental margins; The concentration of salt in the remaining water bodies led to rapid precipitation of the salt. The inset evokes the transit of mammals (e.g. camels and mice) from Africa to Iberia across the exposed Gibraltar Strait.

In the Messinian salinity crisis (also referred to as the Messinian event, and in its latest stage as the Lago Mare event) 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.[1][2]

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 about 5.96 million years ago, sealing the Mediterranean off from the Atlantic.[6] This resulted in a period of partial desiccation of the Mediterranean Sea, the first of several such periods during the late Miocene.[7] 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, wetter 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.[8]

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 kilometres 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.[9]

  1. ^ Gautier, F., Clauzon, G., Suc, J.P., Cravatte, J., Violanti, D., 1994. Age and duration of the Messinian salinity crisis. C.R. Acad. Sci., Paris (IIA) 318, 1103–1109.
  2. ^ Krijgsman, W (August 1996). "A new chronology for the middle to late Miocene continental record in Spain" (PDF). Earth and Planetary Science Letters. 142 (3–4): 367–380. Bibcode:1996E&PSL.142..367K. doi:10.1016/0012-821X(96)00109-4.
  3. ^ Krijgsman, W.; Garcés, M.; Langereis, C. G.; Daams, R.; Van Dam, J.; Van Der Meulen, A. J.; Agustí, J.; Cabrera, L. (1996). "A new chronology for the middle to late Miocene continental record in Spain". Earth and Planetary Science Letters. 142 (3–4): 367–380. Bibcode:1996E&PSL.142..367K. doi:10.1016/0012-821X(96)00109-4.
  4. ^ Retallack, G. J. (1997). "Neogene Expansion of the North American Prairie". PALAIOS. 12 (4): 380–390. doi:10.2307/3515337. JSTOR 3515337. Retrieved 2008-02-11.
  5. ^ "ICS Timescale Chart" (PDF). www.stratigraphy.org.
  6. ^ Cunliffe, Sir Barry (2017-09-29). On the Ocean: The Mediterranean and the Atlantic from prehistory to AD 1500. Oxford University Press. p. 56. ISBN 978-0-19-107534-6. the remnant Tethys became joined to the Atlantic, roughly along the line of what was to become the Strait of Gibraltar. About 5.96 million years ago this gap closed, initiating what is known as the Messinian Salinity Crisis, which lasted for more than half a million years before the Atlantic was reunited once more with the Mediterranean.
  7. ^ Gargani J.; Rigollet C. (2007). "Mediterranean Sea level variations during the Messinian Salinity Crisis". Geophysical Research Letters. 34 (10): L10405. Bibcode:2007GeoRL..3410405G. doi:10.1029/2007gl029885. S2CID 128771539.
  8. ^ Clauzon, Georges; Suc, Jean-Pierre; Gautier, François; Berger, André; Loutre, Marie-France (1996). "Alternate interpretation of the Messinian salinity crisis: Controversy resolved?". Geology. 24 (4): 363. Bibcode:1996Geo....24..363C. doi:10.1130/0091-7613(1996)024<0363:AIOTMS>2.3.CO;2.
  9. ^ Cloud, P. (1988). Oasis in space. Earth history from the beginning, New York: W.W. Norton & Co. Inc., 440. ISBN 0-393-01952-7