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Mid-Atlantic Ocean temperatures peaked in 1998

Cooling since then 'not caused by climate change'

The water temperature in the subtropical Atlantic Ocean has cooled down since 1998, oceanographers report. Measurements since 1957 had shown a rise of more than ¼ of a degree up to that point, but between 1998 and 2006 the ocean stopped warming and cooled by 0.15°C in the same area.

The measurements of sea temperature were carried out along the parallel 24.5 degrees of latitude north of the equator running from the African coast to the Caribbean by Spanish government oceanographers. The oceanographers used a network of "Argo" instrument buoys and survey vessels. The scientists describe the cooling as "unusual".

"The ocean's natural variability mechanisms are more significant than we thought," says Pedro Joaquín Vélez Belchí of Spain's Canarian Oceanography Centre.

In the opinion of Vélez Belchí and his colleagues, the drop in temperature seen in the mid-Atlantic cannot be put down to climate change – in particular they don't consider that meltwater from glaciers or the polar cap is responsible. If that had been the underlying cause, a corresponding temperature drop "should have been observed clearly in the areas close to the North Pole", he says – and none was.

Rather, the oceanographers consider that the cooling may have resulted from wind-driven alterations in the circulation of water.

"Changes in the global structure of winds in the north Atlantic cause oscillations on the ocean's surface layer which can be felt up to 2,000 metres deep," notes Vélez Belchí.

Outline details of the research were announced by the Spanish Foundation of Science and Technology (FECYT) yesterday, ahead of a further expedition intended to glean more data. A study by Vélez Belchí and his colleagues was published in the Journal of Physical Oceanography recently. ®

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