I spent a week in Nice in the middle of June attending a meeting of the European Federation of Biochemical Societies at which I presented a paper. The city is beautifully situated on a curved Mediterranean bay and is flanked on the seafront side by a splendid 5km boulevard, the Promenade des Anglais. My hotel was located on the promenade and I inevitably saw the Mediterranean morning, noon and night.
I was intrigued by the fact that the sea appeared to have no tide. Every time I looked, it was lapping the long curved beach at the same level. It behaves in this respect more like a lake than the sea I am used to around our Irish coasts. On returning home, I read up on the Mediterranean and was intrigued to learn that there is strong geological evidence to indicate that this entire sea dried up millions of years ago.
The idea of the Mediterranean as a lake is confirmed by looking at an atlas. It is an intercontinental sea situated between Europe to the north, Africa to the south, and Asia to the east. It covers an area, excluding the Black Sea, of 970,000 square miles.
The Mediterranean is linked to other major bodies of water only by very narrow connections. To the west it is connected to the Atlantic Ocean by the Strait of Gibraltar, which is only eight miles wide at its narrowest point and has a shallow channel.
To the north-east, the Dardanelles, the Sea of Marmara and the narrow strait of the Bosporus link the Mediterranean to the Black Sea. To the south-east, the Suez Canal links it to the Red Sea.
Surface water continuously flows into the Mediterranean through the Strait of Gibraltar, and this is the sea's major source of replenishment. The most constant component of circulation in the Mediterranean is the current formed by this inflow along the north African coast.
Drilling investigations of the Mediterranean sea-bed in the early 1970s produced evidence that led to the formulation of a fascinating desiccation theory. The geological nature of sands, gravels and other features of the sea-bottom could not be explained as having been formed at the bottom of a deep sea. Recovered gravel from the ocean bottom looked like river gravel.
This is not the sort one would find in an ordinary river that drains a continent, but is typical of a stream that drains a dried-up ocean bottom. Many fossils were also found of species that live in coastal lagoons, not in deep seas. Was the explanation that the Mediterranean had once been cut off from the Atlantic Ocean and had evaporated? Was the Mediterranean, now a deep blue inland sea, once a desert?
The hypothesis put forward to explain the various geological features of the Mediterranean sea-floor is that the sea once vanished. The most likely explanation is that the Strait of Gibraltar was once an isthmus (a narrow strip of land connecting two large land areas) that prevented water flowing freely in from the Atlantic Ocean. The Mediterranean then shrank as the water evaporated under the strong sun, until it eventually became a salt lake, like the Dead Sea only much bigger. Various minerals gradually settled out (gypsum, salt etc) as the evaporation continued, until eventually the sea bottom was laid bare.
Water would occasionally spill over the isthmus at Gibraltar to partially flood the Mediterranean basin, which would again dry out. Many such cycles of flooding and drying out occurred over a million years during the late Miocene period.
Eventually the dam at the Isthmus of Gibraltar broke about five million years ago and the sea water gushed through spectacularly in an enormous waterfall. The Gibraltar Falls were 100 times larger than Victoria Falls and 1,000 times bigger than Niagara Falls. Water came through at a rate of 40,000 cubic kilometres per year. Even at that stupendous rate, it took 100 years to fill the empty Mediterranean basin.
More recent evidence has cast doubt on the above hypothetical scenario. New evidence suggests that the sea floor was never completely dry but was covered by shallow, highly saline waters that deposited large quantities of salt on the ocean bottom.
The disappearance of the Mediterranean was probably not a unique event. Large salt deposits elsewhere in the world indicate there may have been other desiccated oceans. For example, salt deposits under the Gulf of Mexico may have arrived when the gulf was an isolated inland sea undergoing desiccation.
The hypothesis that the Mediterranean basin was once a baked desert exerts a stronger grip on the imagination than the shallow, salty lake scenario. The desiccation theory was put forward by Stephen Hsu (Institute of Technology, Zurich) and others.
Hsu claims that the Strait of Gibraltar is now gradually shoaling up and that in time (2-3 million years) the isthmus will again form and the Mediterranean Sea will again dry out.
It is likely that giant oil reserves lie under the sea floor. These could be very easily exploited in the new desert. Huge hydroelectric plants could be built at the giant Gibraltar waterfall to generate energy. Nice would no longer be a rich seaside resort but a desert outpost where oil workers might amuse themselves in their free time.
Kenneth Hsu has described his hypothesis in his book The Mediterranean Was A Desert: A Voyage of the Global Challenger (Princeton University Press, 1984).
William Reville is a senior lecturer in biochemistry and director or microscopy in UCC