Climate Change and the Ocean

Science presents new evidence

Embargo: , Thursday, February 1st, 2007, 2:00 p.m. Eastern U.S. Time

The world ocean and climate processes display a sensitive interplay: ocean current distribute great amounts of heat between equatorial and polar latitudes. Moreover the world ocean stores considerable quantities of carbon dioxide, and is thereby alleviating the global greenhouse effect. Conversely the human induced climate change influences ocean processes. This is supported by a study by a group of scientists from Australia and Germany which will be published in the upcoming edition of Science (February 2nd). According to these findings, upwelling processes off Northwest-Africa have been intensifying distinctly during recent decades.

Dr. Helen McGregor (University of Wollongong and the Australian Nuclear Science and Technology Organisation) and her co-workers at MARUM Research Center Ocean Margins, University of Bremen, analyzed two sediment cores, which they drilled off Morocco. These marine sediments archive the region’s climate history from 520 B.C. to today. The researchers found that climate induced changes in the ocean have never been more dramatic than in the past decades. According to their analysis, sea surface temperatures in this part of the Atlantic Ocean declined by 1.2 degrees Celsius during the 20th century.

„The seemingly paradox relationship between rising temperatures in the atmosphere and declining sea surface temperatures can be explained easily”, says geoscientist Dr. Mc Gregor, first author of the Science study. Enhanced input of carbon dioxide into the atmosphere means rising temperatures over North West Africa, which lower the atmospheric pressure over the Sahara. In contrast the bordering Atlantic region is dominated by a high-pressure system. Consequently intensified air pressure differences lead to stronger equatorward directed winds: “Both the increasing wind and the rotation of the Earth (Coriolis force) cause coastal surface waters to be transported to the open ocean. These water masses are then replaced by considerably cooler water being upwelled from deeper oceanic levels”, explains Dr. McGregor. “The stronger the greenhouse effect the stronger the cold water pump works - and the cooler the coastal waters off Morocco.”

The findings of the international research team align with evidence from upwelling systems in the Arabian Sea, off the Iberian Peninsula, off California, and Peru. However, those studies only cover shorter periods. “Our sediment cores, which we drilled in 355 metres water depth, are characterized by an exceptionally high sedimentation rate of 210 centimetres per 1,000 years”, says Dr. McGregor. In contrast only two centimetres on the average of material would be deposited on the open ocean sea floor during this space of time. “Therefore we are able to analyze the development of the regional climate for more than 2,500 years with a remarkably high resolution. In places our sampling points in the sediment core were only a few years away from each other, which is extraordinarily good for marine sediments.”

Upwelling systems like that off North-Western Africa are of high economical importance: Although they cover less than one per cent of the global sea surface, about 20 per cent of global fishing takes place there. “Due to this we would be well advised to monitor these sensitive ecosystems in the future”, Dr. McGregor points out. “Since carbon dioxide contents in the atmosphere will continue to rise in the future, we have to anticipate increased upwelling processes off the North-West African coast – but not only there.”


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