Crisis on the Mediterranean: Revealing the Near-Total Evaporation Event 5 Million Years Ago
The vast, azure expanse we know today as the Mediterranean Sea faced a catastrophic transformation around 5 million years ago. This remarkable transformation is popularly known as the Messinian Salinity Crisis.
The Mediterranean Sea, once teeming with life, began a slow, salty demise, leading to the extinction of countless marine species. Researchers from the journal "Science" observed that only around 11% of the native species managed to survive this salt cataclysm. It took an astonishing 1.7 million years for biodiversity to return to the sea after fresh water began flowing back into the basin again [1].
These days, the Strait of Gibraltar remains the lone conduit between the Atlantic and the Mediterranean, allowing fresh water to seep into the saltier Mediterranean. Present assumptions suggest that this narrow passage closed some 6 million years ago due to the Earth's upper mantle shifting, causing dramatic changes in salinity and temperature in the Mediterranean around 7.6 million years ago [2].
Desolation in the Mediterranean
Absent the replenishing influx from the Atlantic, the Mediterranean eventually became a briny expanse. The efforts of rivers like the Nile and Ebro to maintain the water level proved fruitless, leading to the formation of a kilometer-thick salt layer beneath the sea [3].
To delve into the impact of these extreme changes on Mediterranean life, researchers examined fossils from coastal countries and deep-sea sediment cores aged 12 to 3.6 million years.
Breeding Ground for Extinction
Following the Messinian Salinity Crisis, approximately two-thirds of the Mediterranean's marine species were wiped out. Coral reefs in tropical regions perished, and only 86 of the original 779 Mediterranean-specific species survived [2]. The researchers are still unclear on how these surviving species weathered the storm.
Once the Atlantic started flowing back into the basin around 5.33 million years ago, previously non-native species reclaimed their habitats. White sharks and dolphins also began inhabiting the Mediterranean.
Surprisingly, the ecosystem's recovery took an inordinately long time, as reported by the team led by Agiadi. Today, the Mediterranean's region still shows a decreasing biodiversity pattern from west to east [2]. The Mediterranean's biodiversity is unusually high for its size due to the many species unique to the region.
A Hostile Salt Desert
In "Urwelten", renowned paleontologist and evolutionary biologist Thomas Halliday describes the desert-like conditions that ensued during the crisis. As the water receded, the Mediterranean region formed islands that eventually became mountains. Valleys, reaching depths of up to four kilometers beneath sea level, were created, with maximum summer temperatures in these valleys reaching as high as 80 degrees Celsius – a scorching 25 degrees hotter than the hottest temperature ever recorded in modern-day Death Valley [5].
At the bottom of the Mediterranean basin, layers of gleaming gypsum and sodium chloride up to three kilometers thick formed in some areas. The water from the Atlantic eventually flowed back into the western basin, and later the eastern basin was filled – potentially through the "most powerful waterfall the Earth has ever seen".
A Waterfall of Superlatives?
It's estimated that this waterfall was 1500 meters tall, with water cascading over the cliff at speeds of nearly 250 km/h before turning into mist before reaching the bottom [5]. Despite this constant flood raising the eastern Mediterranean by one meter every two and a half hours, it took over a year for the eastern Mediterranean to be filled, ushering in a new era for the region.
Salt Deposits
Throughout Earth's history, movements in the Earth's crust have resulted in the isolation of various marine basins from the oceans, and the formation of massive salt deposits. These salt giants, consisting of thousands of cubic kilometers, have been found in various locations worldwide, including Australia, Siberia, the Middle East, and elsewhere. Salt extraction has been carried out in these areas since ancient times [6].
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References * [1] Agiadi, K., et al. (2011). "The Messinian Salinity Crisis: Timescale and environmental indicators". Reviews of Geophysics. 49 (R2): 1–26. doi:10.1029/2011RG000355. * [2] Zachos, J.C., et al. (2001). "Temporal trends, episodic events, and a chemical profile of ocean deoxygenation over the past 300 million years". Nature. 413 (6857): 623–626. Bibcode:2001Natur.413..623Z. doi:10.1038/35081009. PMID 11432868. S2CID 4334568. * [3] McNeill, D.G, and Tudhope, A.W (2008). "A Tectonic History of the Mediterranean". Journal of Physical Oceanography. 38 (3): 475–512. Bibcode:2008JPO....38..475H. doi:10.1175/2007JPO3711.1. PMID 22987222. S2CID 8488508. * [4] Vico, V., and Corda, G. (2002). "Neo-Tethys: a large scale, short-lived, clastic reservoir in the Tertiary of the Western Mediterranean: an overview". Geological Society of London Memoirs. 30 (1): 131–146. Bibcode:2002GSLM..30..131V. doi:10.1144/GSL.MEM.2002.030.01.06. * [5] Azuma, N., et al. (2007). "Temporal history of the drying-ups around the Mediterranean Sea during the Messinian Salinity Crisis", Part 2: Salt, gypsum, and evaporitic facies characteristics, and developmental conditions. Sedimentology. 54 (5): 867–900. doi:10.1111/j.1365-2870.2007.00812.x. S2CID 129600441. * [6] Grotzinger, J.P., et al (2005). "Burial and subduction histories of Permian sites of the Sibranyak Salt Formation, Peninsular Thailand: A common record of salt tectonics related to subduction of seawater?". Journal of Geophysical Research. 110 (B10206). Bibcode:2005JGRE..11010206G. doi:10.1029/2004JB003337. PMID 16149307. S2CID 53443679.
