February 25, 2009

Seesaw Link Between North And South Atlantic Climates

A new study released Wednesday shows that large, sudden climate changes in the North Atlantic have a rapid impact on the South Atlantic, and also affect weather throughout the entire world.

An international team of scientists, led by researchers at Cardiff University, found that significant, abrupt temperature changes recorded over Greenland and the North Atlantic during the last Ice Age were actually global in their extent.

The new research supports the idea that changes in ocean circulation within the Atlantic played a central role in abrupt global-scale climate changes.

Using a sediment core taken from the seafloor in the South Atlantic, the researchers were able to create a detailed reconstruction of ocean conditions in the South Atlantic during the final phases of the last ice age.

"During this period very large and abrupt changes in temperature were observed across the North Atlantic region. However, evidence for the direct transmission of these shifts between the northern and southern hemispheres has so far been lacking," said Dr. Stephen Barker, Cardiff University's School of Earth and Ocean Sciences and the study's lead author.

The research suggests that abrupt changes in the north were accompanied by equally abrupt but opposite changes in the south. It provides the first concrete evidence of an immediate seesaw connection between the North and South Atlantic.   For example, the data shows that an abrupt cooling in the north would be accompanied by a rapid southerly shift of ocean fronts in the Southern Ocean, followed by more gradual warming across the south.

"The most intuitive way to explain these changes is by varying the strength of ocean circulation in the Atlantic. By weakening the circulation, the heat transported northwards would be retained in the south," Dr Barker explained.

"Our new results agree with climate models that predict a rapid transmission of climate signals between the two hemispheres as a consequence of abrupt changes in ocean circulation," said Dr. Gregor Knorr, the study's co-author and a climate physicist based at Germany's Alfred Wegener Institute.

The study has wide implications for our understanding of sudden climate change.

"While it is unlikely that an abrupt change in climate, related to changes in ocean circulation, will occur in the near future, our results suggest that if such an extreme scenario did occur, its effects could be felt globally within years to decades," said Dr. Ian Hall, School of Earth and Ocean Sciences, said.


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