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Wednesday, 14 June, 2000, 18:02 GMT 19:02 UK
Mediterranean waters take a dive
The Med has fallen rapidly since the 1960s
Global warming may be raising sea levels in the rest of the world, but the waters of the Mediterranean are falling - and fast.

New research shows the Mediterranean has lowered by about three to five centimetres in the past 40 years.

Dr Michael Tsimplis, of the Southampton Oceanography Centre, UK, says different climate effects and dam building are increasing the salinity of the water.

This makes its density go up and its volume go down. Dr Tsimplis told BBC News Online: "The fall is in the range of one to 1.4 millimetres per year," which has returned the sea to levels not seen since the early 19th Century.

The research is reported in New Scientist magazine.

Control stations

It is based on data from tide-gauge stations.

There are less than ten stations in the Mediterranean with long and reliable records, and most these are in north west of the region and the north Adriatic. Different land movements on either side of the sea also complicate the data.

Nevertheless, Dr Tsimplis says, the downward trend is clear.

"It is even more dramatic if one considers the control stations which are located in the Atlantic and the Black Sea. The Black Sea continues to go up by approximately two millimetres per year and the Atlantic still goes up by 1.2 millimetres per year."

Many scientists believe the burning of fossil fuels is affecting the Earth's climate system, raising average, global, surface temperatures. Existing tide-gauge data from around the world and computer projections suggest thermal expansion of the oceans will lead to a general rise in sea levels.

Dam building

But Dr Tsimplis believes a very specific climate phenomenon is working against any such rise in the Mediterranean.

He thinks the North Atlantic Oscillation may be at play. This is a natural and recurring pressure pattern that has a profound impact on the weather experienced in the North Atlantic region and surrounding continents.

The Southampton researcher says this could have led to increased evaporation over the Mediterranean area, which in turn increased the salinity of the water.

More dam building in the region after 1960, which has reduced the amount of fresh water running into the sea, may also have exacerbated the trend.

The original research, co-authored with Dr Trevor Baker, was published in Geophysical Research Letters.

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