Mediterranean flooding shows threats from global warming

A cataclysmic flood could have originated the Mediterranean Sea as we know it today, filling what was then — millions of years ago — a dry basin. The dramatic flooding likely took only a couple of years or less, a period of time actually close to nothing in a geological scale.

According to a new model, whose calculations have been published on the Dec. 10 issue of Nature, the flood’s peak water poured from the Atlantic into the Mediterranean basin at a rate one thousand times the flow of the Amazon River. A speed of change high enough to cast serious issues on the possible consequences of a swift melting of the North Pole’s ice because of global warming.

“In an instantaneous flash, the dry Mediterranean became a normal Mediterranean like we see it today,” says lead author Daniel Garcia-Castellanos of Spain’s Consejo Superior de Investigaciones Cientificas (CSIC) in Barcelona.

Calculations show that 100 million cubic meters of water flowed through the channel at 100 kilometers an hour: the team of researchers compare it to a torrent several kilometers wide at a fairly gradual slope. Waterlevel rose by more than 10 meters a day, eroding some 40 centimeters of rock. “It would be an exciting rafting place,” commented Garcia-Castellanos.

The flooding had a doubtlessly positive outcome: it allowed the region to escape becoming a desert. The sea had separated from the world’s oceans 5.6 million years ago and eventually desiccated by evaporation in a period geologists call the Messinian salinity crisis. Luckily, 5.3 million years ago water from the Atlantic Ocean found a way back in to the drying seabed through what is now the Strait of Gibraltar between Spain and Morocco. Geologists figured the resulting flood must have been impressive, but their estimates for how long it took have varied wildly, from 10 years to several thousand years.

“The record of the Mediterranean tells us that the transition from the dry, high salinity situation to the normal open water situation we have nowadays was very rapid,” Garcia-Castellanos says. “But ‘rapid’ in geology could mean many tens of thousands of years.”

Using equations derived from observations of mountain rivers, the team of researchers modeled how the flood might have progressed: The flood started gradually, but as the sill between the Atlantic and the dry Mediterranean wore down, the rate of water flowing and rock eroding increased exponentially. As more water flowed over the sill, more rock wore away, allowing ever more water to spill in.

The calculations show an upper limit of two years for how long it took to fill the Mediterranean. But Garcia-Castellanos says it could have been as short as a few months. The energy carried in such a flood is comparable to the heat transport along the Gulf Stream in a year, or 4 percent of the kinetic energy of the meteorite impact thought to have killed the dinosaurs.

The flood would have had a dramatic effect on local ecosystems, and could even have affected the global climate. The model suggests that global sea level dropped 9.5 meters as a result of the flood. The team points out that a much smaller flood in North America 12,000 years ago has been linked to a worldwide cold snap, and suggests that the Mediterranean flood may have had similarly significant effects.

through the channel per second, with water gushing at speeds of 100 kilometers an hour

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