After a long time converted into a dry and saline lake, the basin was flooded again with water from the Atlantic
An investigation by the Australian National University (ANU) delves into what happened in the Mediterranean during the mega-flood that it suffered five million years ago and that helped give it its current configuration. During the process, a giant waterfall 1.5 kilometers high occurred in the area of present-day Sicily that helped fill the entire eastern half of the Mediterranean basin with water.
The event, called the Zanclean Mega-Flood, was the largest flood known to science. It transformed the Mediterranean basin from a barren brine pond to the bustling marine ecosystem we know today. The ANU study, published in Nature Geosciencesheds light on how this transformation occurred.
Today it is possible to find seashells in the largest mountain range of the island, the Troodos Mountains. This is so because the Mediterranean has had a tumultuous history full of tectonic activity, islands that sink and rise, and floods.
Lead author and ANU PhD researcher in paleoenvironments Udara Amarathunga states that the Zanclean flood it was one of the most abrupt global environmental changes since the mass extinction that wiped out the dinosaurs. The researcher considers that it was “the rebirth of the Mediterranean & rdquor ;.
Gibraltar’s ‘door’ closes
“The mega-flood triggered the end of the Messinian Salinity Crisis (MSC) when the Mediterranean basin partially dried up as the Atlantic-Mediterranean gateway closed [Gibraltar]leaving huge deposits of salt and killing most life forms& rdquor ;, he explains in Cosmos magazine.
Amarathunga added that the MSC began six million years ago when the European and African continental plates pushed against each other, separating the Mediterranean from the Atlantic at the point where Gibraltar is today.
This “door”, says Amarathunga, “was not completely closed and allowed a small amount of entry to the Mediterranean. But it closed completely 5.6 million years ago, and this is the peak of the salinity crisis & rdquor ;.
Although scientists aren’t sure of the exact extent of the Mediterranean’s drying up, Amarathunga says they believe its levels dropped by 1-2 kilometres, creating two different basins: an eastern and western basin separated by what is now Sicily.
A gigantic waterfall 1.5 kilometers high
But what happened so that the Mediterranean ceased to be an inhospitable lake of brine?
Slowly but surely, explains Amarathunga, erosion at Gibraltar caused small amounts of water to seep from the Atlantic into the Mediterranean. The mega-flood hypothesis was first elaborated in 2009 by the Spanish scientist Daniel García-Castellanos, who suggested that, after this initial slow flow, the “dam wall” would have broken and caused a massive volume of water to enter the Mediterranean Sea.
This would have formed a gigantic waterfall 1.5 kilometers high at the height of Sicily, which would have finished flooding the other half of the basin.
The energy produced by the massive movement of water in a single day at the peak of the flood would have been equivalent to 500 times the energy produced by Niagara Falls in an entire year. It is estimated that the Mediterranean Sea would have risen more than 10 meters per day at the peak of the flood.
The rest of the world’s seas dropped nine meters suddenly
“It would have been the most abrupt flood in recorded history & rdquor ;, says Amarathunga. The magnitude of the phenomenon was such that “as the Mediterranean filled, andhe global sea level has dropped by about nine metres”.
Immediately after the flood surface of the eastern Mediterranean, there is an “organic-rich layer & rdquor; showing low oxygen levels in the water, as oxygen leads to oxidation of this organic matter. This layer does not appear in the western basin. So these anoxic dead zones in the eastern Mediterranean indicate that the eastern basin was anoxic after the flood.
The megaflood and the deposition of layers rich in organic matter occurred in stages.
The western Mediterranean basin fills up first. Then, once the land barrier that existed at the height of Sicily is broken, a gigantic waterfall is produced to the east. But this waterfall, Amarathunga’s work shows, would have carried large amounts of salt with it to the eastern basin.
“Our interpretation is that towards the end of the flood, both basins mix. But due to the energy of the flood water, all the salt is transferred from this waterfall to the eastern basin & rdquor ;, says Amarathunga. “Now this salt needs to be transferred to the Atlantic. We used another model to estimate the time it would take to get the salt out into the Atlantic.”
“Our work indicates that it took another 26,000 years to remove all the excess salt and return to the Mediterranean the appearance of a normal marine basin & rdquor ;, he adds.
This long transition period was unknown to scientists until now. However, the megaflood hypothesis is subject to some controversy. Some scientists suggest that the Mediterranean never dried up on a large scale. But This new ANU study provides evidence that strengthens the mega-flood hypothesis.
Amarathunga said such a rapid and large transformation is rare, making the Zanclean flood a unique example of how quickly entire ecosystems can change.
Reference study: https://www.nature.com/articles/s41561-022-00998-z
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