A massive environmental calamity rocked the ancient Mediterranean. It took millions of years for the ecosystem to recover.
In the late Miocene epoch, roughly 5.9 million years ago, calamity befell the Mediterranean Sea. In a period of roughly 600,000 years, tectonic uplift sealed the gateway between Europe and North Africa, cutting the basin off from the Atlantic Ocean. Suddenly—geologically speaking—the Mediterranean was an inland sea. Before that, “you can imagine a nice tropical place with tropical reefs everywhere,” says Konstantina Agiadi, a geoscientist and paleontologist at the University of Vienna in Austria.
But soon, the Mediterranean began to evaporate, the vibrant seascape transforming into a series of barren, briny lakes. As it receded—dropping in some places by up to two kilometers—the water left behind a vast layer of gypsum and salt, containing about five percent of all the salt in the ocean. Scientists call it the Mediterranean salt giant.
As the salinity soared, wildlife in the basin struggled, water circulation ground to a halt, and the concentration of dissolved oxygen plummeted. Then, as abruptly as the first time, the Earth lurched again. Tectonic activity lowered the land barrier and the Atlantic came crashing back in. The Mediterranean Sea was reborn. But it would never be the same.
Of the Mediterranean’s profusion of unique local wildlife, just 11 percent, a mere 86 species, survived this so-called Messinian salinity crisis. Everything else—the corals, the grasses, the reef fishes—were wiped out and replaced by Atlantic species. But the rebuilt ecosystem paled in comparison to what was lost. And according to two new papers recently published by Agiadi and her colleagues, even 1.7 million years after the Mediterranean reflooded, the ecosystem still had not fully recovered.
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