Drying Out the Mediterranean: A Close Look at the Devastating Salt Cataclysm 5 Million Years Ago
Once a bustling marine haven, the Med riding high with life, took a drastic turn about 5 million years ago, undergoing a shocking transformation. This unprecedented event became legendary as the Messinian Salinity Crisis.
Researchers shed light on this catastrophe in the renowned journal "Science", revealing that only around 11% of the region's indigenous marine species managed to survive this saltpeter storm. It took an astonishing 1.7 million years for biodiversity to make a strong come-back once fresh water returned to the basin again [1].
In the present day, the Strait of Gibraltar remains the lone passage connecting the Atlantic and the Mediterranean, acting as a lifeline allowing fresh water to seep into the saltier Mediterranean. Moreover, geologists suggest that this narrow passage closed approximately 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].
A Desolate and Salt-Coated Sea
The absence of the Atlantic influx left the Mediterranean in a bind. With rivers like the Nile and Ebro fighting a losing battle to maintain water levels, the sea eventually succumbed to becoming a briny expanse, eventually forming a kilometer-thick salt layer underneath [3].
Diving deep into the fingerprints of this sea-change, researchers scrutinized fossils from coastal countries and deep-sea sediment cores aged 12 to 3.6 million years.
A Playground for Extinction
Following the Messinian Salinity Crisis, around two-thirds of the Mediterranean's marine species faced extinction. Coral reefs in tropical regions crumbled, while only 86 of the original 779 Mediterranean-specific species clung on [2]. Scientists are still in the dark regarding how these resilient survivors endured the crisis.
As the Atlantic began continuing its flow into the basin around 5.33 million years ago, previously absent marine species swiftly snatched up their habitats. White sharks and dolphins, for instance, found their way back into the Mediterranean.
Interestingly, the ecosystem's recovery was a slow burn, as per the team led by Agiadi, with the Mediterranean's region still exhibiting a decreasing biodiversity pattern from west to east [2]. The crypto-zealous Mediterranean's biodiversity is unusually high for its size, owing to the many species unique to the shimmering sea.
An Infernal Salt Desert
In "Urwelten", Thomas Halliday, the esteemed paleontologist and evolutionary biologist, vividly paints the torrid conditions that ensued during the crisis. As the water levels dwindled, the Mediterranean region morphed into arid islands, eventually transforming into jagged mountains. The cradle of valleys formed, reaching depths of up to four kilometers below sea level. The summer temperatures in these valleys rose to a sweltering 80 degrees Celsius, constituting a scorching 25 degrees hotter than the sun-scorched Death Valley in today's times [5].
During the great recession, layers of gleaming gypsum and sodium chloride up to three kilometers thick formed in certain areas. Eventually, water from the Atlantic seeped into the western Mediterranean, and later, the eastern Mediterranean basin was filled from below - possibly through the "most powerful waterfall the Earth has ever seen".
A Gush of Marvels?
Estimates suggest that this waterfall stood at 1500 meters tall, with water cascading over the edge at breathtaking speeds of nearly 250 km/h before transforming into mist before touching the ground [5]. The constant torrent added an impressive meter to the eastern Mediterranean's depth every two and a half hours, but the long haul saw the eastern Mediterranean filled only over the course of a year, ushering in a new era for this desolate sea.
Salt Volumes Across the Ages
Throughout Earth's history, jagged shifts in the Earth's crust have led to the temporary isolation of marine basins from the oceans, culminating in the formation of massive salt deposits. Atlasing these salt titans, spanning thousands of cubic kilometers, has been common across Australia, Siberia, the Middle East, and other regions. Salt extraction from these areas has a rich history, dating back to 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.
