Evaporation infuses its waters with an extra dose of salt, which spills into the Atlantic and helps drive oceanic conveyor belts that circumnavigate the planet, influencing temperatures, storm patterns, and more. As modern temperatures continue their steady march upward, and the ice caps dwindle at the poles, it's "pretty blooming important" to figure out what processes led to the planet we see today, says Rachel Flecker , a geologist at the University of Bristol.
The only water source keeping the body stable is a steady flow from the neighboring Atlantic Ocean, pouring through a narrow channel between Spain and Morocco, the Strait of Gibraltar.
Many millions of years ago, tectonic shifts deep below the surface may have forced the landscape upward, crimping the vital connection between the Mediterranean and Atlantic. Waters likely continued to flow into the basin, but the shift would have severed the escape route for dense saline currents running along the basin floor to reach the open ocean.
Some researchers suggest the region nearly dried up before the flood, leaving a cavernous basin dipping more than a mile below current sea level. All that stood between the empty basin and the mighty Atlantic may have been a narrow spit of land where the Gibraltar Strait is today though the exact width of this former land bridge is still uncertain.
Some 5. The breach likely started as a trickle over the natural dam connecting modern-day Europe to Africa, according to their models from a study. But erosion quickly took over.
As the water mounted, it scoured out a deepening path that allowed still more water to pass. At its peak, the flow may have gushed at million cubic meters per second, filling the sea in two years or less. Such an event would have excavated at least million olympic swimming pools worth of sediment, cutting a channel through the Strait of Gibraltar and carving a canyon that extends into the seafloor.
The cataclysmic event transformed the entire region, moving not just water but also cutting away chunks of rock, sand, and anything else in the way. They required evidence from modern processes to prove an ancient event could have occurred. Scientists first began digging into the history of the Mediterranean as early as the s , when they found salt deposits on the shores hinting at a particularly briny ancient sea. Features that resembled the cracked surface of a mudflat when left to bake in the sun were found embedded in the upper layers of salt—a hint that waters may not have always been sloshing above, Ryan says.
Over the years, many researchers have dipped their toes into the puzzling waters, and as more evidence accrues, the more perplexing the situation becomes. Throughout the basin, fossils of critters can be found that point to a Mediterranean nearly full of water just before it reconnected to the Atlantic, says Wout Krijgsman , a geologist at Utrecht University in the Netherlands.
Perhaps before the flood swept in, the region was not a desert but a shrunken sea. An estimated cubic miles of sediment would have been strewn across the Mediterranean basin, collecting in pockets where the water flow was low. But the sediments, laid long before people first set foot in the region , are now buried beneath the seafloor.
Only a series of salty or brackish lakes might have survived. Eroded channels and sediment deposits in what might have been the ancient surface of the exposed Mediterranean basin seem to support this theory. The period of the dry Mediterranean might have ended quickly when the Strait of Gibraltar reopened 5.
Seismic reflection imaging, a technique that relies on sound waves to image what lies underground, has revealed that beneath kilometer-deep Quaternary sediments, a huge erosion channel extends across the strait. Researchers think that this channel might have been carved during the flood as Atlantic waters rushed in to refill the Mediterranean. First, the connections between the Atlantic and the Mediterranean may have closed due to tearing and sinking of the lithosphere pic.
Looking for evidence to support this theory called the Zanclean flood hypothesis , an international group of researchers recently identified buried sediments that could have been deposited by the flooding waters. Using computer simulations to recreate the opening of the strait and the subsequent flood, Garcia-Castellanos and his team identified low-flow areas that were likely to accumulate sediments.
Then, they looked at seismic profiles of these areas to see if they could find the sediments. On the lee side of an ancient volcanic cone in the predicted path of the flooding, they found a large sediment deposit. It appears as an amorphous blob in the seismic profile, in contrast to the neatly stratified layers of marine sediments around it, suggesting rapid sedimentation.
Its shape and size also seem to match the likely direction of the flood. In , the same group of researchers found similar deposits near a deep underwater gorge in the Malta Escarpment, the natural barrier separating the eastern and western Mediterranean basins. This gorge, known as the Noto Canyon, is the most likely location where the flood might have spilled over the escarpment to refill the eastern Mediterranean basin.
The main limitation of these simulations is the lack of knowledge about ancient seafloor topography. This natural barrier, called the Malta Escarpment, towers more than three kilometers high in some places and is located to the east of modern-day Sicily and Malta.
The new study, led by Aaron Micallef, a marine geologist at the University of Malta, found the sediments buried near Sicily were likely deposited by the megaflood—a finding that implies a violent influx of water throughout the Mediterranean. Micallef and his colleagues focused on the Malta Escarpment because megaflood water flowing east would have encountered this natural blockade, making it a logical place to find sediments deposited by water that breached the cliff.
The researchers used seismic reflection imaging, which involves directing sound waves toward the sea bottom and measuring the time it takes them to return. Essentially an x-ray of the seafloor, this technique allowed the team to reconstruct the thickness and likely composition of buried sediment layers.
One of those layers stood out from the others; it was a jumbled mix of angular pebbles and boulders. Furthermore, this layer lay just to the east of Noto Canyon, a large undersea gorge running through the Malta Escarpment.
The canyon bears a curious geologic scar on its western side; a channel meters deep runs through its hard limestone. This feature, similar to the signatures of erosion seen near the Strait of Gibraltar, was probably caused by flowing water, the researchers reasoned. The scientists estimated water coursed over the escarpment through Noto Canyon, flowing at up to kilometers per hour and spilling over a 1.
Micallef and his team have hypothesized, based on earlier calculations by Garcia-Castellanos and his colleagues, that the torrent boosted the sea level in the eastern Mediterranean by at least 10 meters per day, refilling the entire sea in just a few years.
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