|United Nations University - Work in Progress Newsletter - Volume 15, Number 2, 1998 (UNU, 1998, 12 pages)|
By François Doumenge
In his magisterial work on the Mediterranean world in the age of Philip II, Fernand Braudel introduces that body of water as a "complex of seas." Over and again, he demonstrates the intricate interplay of forces that have shaped the ecology of the Mediterranean World and still influence it today. The great Biblical flood of Noah, this article shows, may have left the sea in a state of imbalance that affects the catch modern-day Mediterranean fishermen.
Dr. Doumenge has impressive credentials for his long-term historical look at the Mediterranean environment. He is the successor to Jacques Cousteau as Director of the Oceanographic Institute in Monaco and as Secretary General of the International Commission for the Scientific Exploration of the Mediterranean Sea (CIESM). Founded by Prince Albert I in 1914, CIESM is one of the oldest international scientific bodies. During more than eight decades, through two world wars, CIESM has engaged in all aspects of marine research - from marine geology to fisheries and chemical pollution. The following article is excerpted from Dr. Doumenge's UN University lecture "The Mediterranean Crises," which is presented in Environmental Change and the Mediterranean, published in 1997. - Editor
I want to talk about the Mediterranean crises - geophysical, geological and biological - that occurred at different time scales: million of years ago, thousands of years, and in the 20th century.
To start, we must look at a time when the Mediterranean Sea was dry and life disappeared - some five million years ago (Figure 1) during the Messinian period. At that time, the Strait of Gibraltar became blocked and, over a period of 100,000-200,000 years, the water had evaporated quite completely. Prior to that, for about a million years, the opening of the Mediterranean had been sometimes from the east and sometimes from the west - there was a balance.
* For sources, see Environmental Change and the Mediterranean (UNU Lectures 16, 17), 1997.
The dry Mediterranean basin was like the Sahara, but with basic level 3,000 metres below sea level. On the bottom of the basin, there are giant rock salt deposits with a total volume of 1 to 1.5 million cubic kilometres. The thickness of these strata is between 800 m in the Baleares basin (in the western Mediterranean) to 1,800 m in the Levantine basin (in the east); sometimes they are as deep as 2,000-2,500 m. These deposits might be seen as the most important reserve of oil and gas of all the world - but under 3,000 m of water!
During this period, the Mediterranean was functioning exactly like the present Sahara system, with large central salty chotts, sebkhas, and wadi - or depressions - running from the mountains at the peripheries. Subsequently, with the opening of the Strait of Gibraltar, the basin was filled again - but first by the Atlantic and only later by the Red Sea. It was thus repopulated first by cold water species, key to an understanding of its modem ecology. From 5 million years ago, the Mediterranean has been a tropical area settled by species of cold-water origin. This is the paradox explaining the fragility and the incapacity of the present Mediterranean to have a stable population.
Second Crisis -18,000 Years Ago
A second, more recent, major crisis occurred about 18,000 years ago - at the end of the last European or Wurm ice age. At that time, the general level of the Mediterranean was about 120 metres less than the present as were seas the world over, which were locked up in ice. The northern and central Adriatic Sea emerged, the Black Sea was still a quite small freshwater lake, and there was a smaller passage at the Strait of Gibraltar, with only about 30 per cent of its present capacity. The water exchange from the incoming Atlantic was reduced, as was the evaporation.
Looking at average temperatures in winter and summer [February (Figure 2A) and August (Figure 2B)], it is very important to note that at that era there was not one Mediterranean Sea, but three. On the east, in the Levantine basin, the temperature range in winter was from 15°C-21°C, and between 21°C-25°C in summer; it remained tropical, and warmer species were able to survive in that small area. There was a "tongue" of cool, desalinated water running out from the Black Sea and extending as far as the coast of Libya; this acted as a thermic wall, cutting off the Levantine from the Central basin.
The Central basin was more or less like the present-day Mediterranean - temperatures in the winter up to 11 °C and in the summer between 19°C and 24°C. The Western basin, however, was like the North Sea or the Sea of Norway - temperatures from 5°C-9°C during winter and 12°C-16°C in the summer. There were subarctic fauna - whales, penguins and seals. This explains why even today there remains in the Western basin a huge population of more than 3,000 blue whales.
The Sapropel: All Life Extinguished
The next Mediterranean crisis was 8,000 years ago - when what we call a "sapropel" phenomenon occurred. This is a general mortality of all marine organisms brought on by changing hydrological conditions, which can happen in the very short time of 50-60 years. This one happened around 6,000 BC, or just at the passage of Egyptian civilization from pastoralism to the Pharaoh state. This was also an historical time associated with the story of the deluge, the Biblical account of Noah's flood.
* For sources, see Environmental Change and the Mediterranean (UNU Lectures 16, 17), 1997.
It appears that heavy rain which caused the deluge, falling in the Middle East and extending down to the lake basins of the East African Rift Valley, enormously increased the water level of the Nile. Its capacity became something like the present-day Amazon. Due to this gigantic increased runoff, the Eastern part of the Mediterranean became covered, in a short period of 40 to 60 years, with a superficial freshwater layer. This, in turn, caused a stratification phenomenon: freshwater at the surface cut the communication between atmosphere and sea water - and all marine life under the freshwater layer died from lack of oxygen. A sapropel formation - some 20 cm of black organic matter at the bottom of the Mediterranean - was discovered in 1952. It caused quite a surprise - but after study by thousands of drillings, it was confirmed that in a very short time all life in the sea had indeed died.
A similar crisis occurred in the Black Sea more recently. Until about 7,450 years ago (plus or minus 130 years), the Black Sea remained a freshwater lake. It started to change, however, as the sea level rose and the Mediterranean entered the Black Sea basin. The deposition of aragonites indicates general aquatic mortality over approximately 5,000 years. The layer also correlates with some very straight data: like the explosion of Santorin Island, and a subsequent lethal deposit of volcanic ash in the Mediterranean.
Need for Many Disciplines
These crises in the Mediterranean are important to understand, because they help with an explanation of what could happen if we have climate changes. The data show that hydrology, sedimentolgy and biology interact together. It clearly demonstrates that without a multidisciplinary approach, you cannot understand the Mediterranean basin.
We have had ample demonstration from recent history that the sapropel is not just a theory. After the Gulf War in 1991, we had a pre-sapropel situation which came very close to a major disaster. Smoke clouds from the burning oil wells in Kuwait covered the Arabian Peninsula, the Persian Gulf, and reached East Africa. They created a weather situation - excessive cold and monsoon-like rains - which could have replicated the conditions that brought on Noah's flood and again threatened all marine life in the eastern Mediterranean. Fortunately, the international community was able to extinguish the fires in time. As it was, the winter of 1991-92 saw more snow and freezing weather than usual in the Middle East.
De Lesseps Lives
Let us now turn to a Mediterranean crisis from the present century, which indicates what a small rise in sea level can mean. As I noted, the Mediterranean is a warm sea populated by cold species. The present level of the Red Sea is about 1.2 m higher than the Mediterranean, and pressure pushes water northward. The Nile used to act as a freshwater barrier at the entrance of the Suez Canal. But the Aswan Dam has cut the river's freshwater flow to less than 10 per cent of the previous level. As a result, the Suez Canal is an open gate for Red Sea water to run into the Mediterranean.
This transfer phenomenon was named Lessepsian migration, after the famous constructor of the Suez Canal, Ferdinand de Lesseps. Fisherman on the Israeli coast in recent years have reported catching more Red Sea species than they do Mediterranean. Every year, five to ten new species from the Red Sea, and even the Indian Ocean, are discovered in the Mediterranean. Ironically, the Mediterranean may be returning to the pre-Messinian situation of millions of years ago, when the marine life was in balance. It is a test of the fragility and capacity for change of these ancient waters. Mankind has shown that it can change the environment and create crisis conditions in a very short period of time as compared with the geological timescale.