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Oceans in a changing climate

08 Awst 2007

Scientists at Cardiff University are contributing to a major study addressing whether global warming could make European winters colder.

Researchers in the School of Earth, Ocean and Planetary Sciences have found a link between changes in the North Atlantic climate and the speed of deep ocean currents over the past 230 years.

In the seas between Greenland, Iceland and Norway, density and temperature differences cause cold, salty water to sink. Part of these dense water masses flow between Iceland and Scotland and are called ‘Iceland-Scotland Overflow Water’. They, in turn, contribute to North Atlantic Deep Water, a current that hugs the seafloor as it traces a path around Africa before joining deep waters surrounding Antarctica and later the Pacific Ocean. Water returns to the northern Atlantic through a series of surface currents such as the Gulf Stream; this global ocean conveyor regulates climate by redistributing heat across the world's oceans.

Dr Karin Boessenkool and Dr Ian Hall from the School of Earth Ocean and Planetary Sciences worked with researchers at the University of Cambridge and Bedford Institute of Oceanography in Canada to study a sediment core from the subpolar North Atlantic. The sediment revealed variations in the flow speed of Iceland-Scotland Overflow Water over the past 230 years linked to changes in the North Atlantic climate.

"Understanding the circulation of the global ocean is of major importance in our understanding of the climate system. It will improve our ability to predict and identify human-induced global change and its consequences for climate," said Dr Boessenkool.

The scientists found that the flow of Iceland-Scotland Overflow Water was more vigorous during periods with low Atlantic storm activity over Europe and slower during prolonged periods when there were more Atlantic storms and depressions getting into northern Europe.

The study is supported by the Natural Environment Research Council and is part of a national programme aimed at improving scientists’ ability to quantify the probability and magnitude of future rapid change in climate. It is published in the journal Geophysical Research Letters.