CANNES. Monte Carlo. St Tropez. Magic names, all鈥攁nd much of the
enchantment comes from the cerulean water that laps their shores.
But what if somebody pulled the plug? Suppose the Mediterranean Sea were to
vanish, leaving behind an expanse of salt desert the size of India.
Hard to imagine? It happened.
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鈥淚t would have looked like Death Valley,鈥� says Bill Ryan, from the
Lamont-Doherty Earth Observatory in New York, one of the leaders of the team
that discovered the Mediterranean had once dried up, then refilled in a deluge
of Biblical proportions. Between five and six million years ago, the great
desiccation touched off what scientists call the Messinian Salinity
Crisis鈥攁 global chemical imbalance that triggered a wrenching series of
extinctions and plunged the Earth into an ice age.
The story came to light in 1970, when an international team chugged across
the Mediterranean in a drilling ship to study the seafloor. Strange things
started turning up in core samples: layers of microscopic plants and soil
sandwiched between beds of salt more than two kilometres below today鈥檚 sea
level. The plants had grown in sunlight. Could the seafloor once have been near
a shoreline?
That question led Ryan and his fellow team leader, Kenneth Hs眉, to piece
together a staggering chain of events. About 5.8 million years ago, they
concluded, the Mediterranean was gradually cut off from the Atlantic Ocean when
continental drift pinned Morocco against Spain. As the opening became both
narrower and shallower, the deep outward flow from sea to ocean was gradually
cut off, leaving only the shallow inward flow of ocean water into the
Mediterranean. As this water evaporated, the sea became more saline and
creatures that couldn鈥檛 handle the rising salt content perished. 鈥淭he sea鈥檚
interior was dead as a door nail, except for bacteria,鈥� says Ryan. With only
rivers to feed it, the Mediterranean dried up and died.
Meanwhile, the evaporated water was falling back to Earth as rain. When the
freshwater reached the oceans, it made them less saline. With less salt in it to
act as an antifreeze, parts of the ocean that would not normally freeze began to
turn to ice. 鈥淭he ice reflects sunlight into space,鈥� says Ryan. 鈥淭he planet
cools. You drive yourself into an ice age.鈥�
Eventually, a small breach in the Gibraltar dam sent the process into
reverse. Ocean water cut a tiny channel to the Mediterranean. As the channel
enlarged, the water flowed faster and faster, until the torrent ripped through
the emerging Strait of Gibraltar at more than 100 knots. 鈥淭he Gibraltar Falls
were one hundred times bigger than Victoria Falls and a thousand times grander
than Niagara,鈥� Hs眉 wrote in his book The Mediterranean was a
Desert (Princeton University Press, 1983).
The rising waters drowned the falls and warm Mediterranean water began to
escape to the Atlantic, reheating the oceans and the planet. The salinity crisis
ended about 5.4 million years ago. It had lasted roughly 400 000 years.
Subsequent drilling expeditions have added a few wrinkles to Ryan and
Hs眉鈥檚 scenario. For example, researchers have found salt deposits more than
two kilometres thick鈥攕o thick, some believe, that the Mediterranean must
have dried up and refilled many times. But those are just geological details.
For tourists the crucial question is, could it happen again? Should Monaco start
stockpiling dynamite?
Not yet, says Ryan. If continental drift does reseal the Mediterranean, it
won鈥檛 be for several million years. 鈥淪ome future creatures may face the issue of
how to respond to nature鈥檚 closure. It鈥檚 not something our species has to worry
补产辞耻迟.鈥�