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Oceans: Drake Passage seen as mixing ground

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Strong storms help push water through the Drake Passage, and beneath the surface, the surging currents help mix the ocean from top to bottom. bberwyn photo.

Underwater mountains help churn up the ocean, fueling the carbon cycle

By Summit Voice

FRISCO — The Drake Passage, between the tip of South America and the Antarctic Peninsula, is well known for wild storms and big swell, but it turns out that turbulence isn’t just at the surface.

Far beneath the breaking whitecaps, the area is a crucial ocean mixing ground, where surface water is exchanged with deep water as currents rush over undersea mountains. Those mixing of water layers are crucial to regulating the Earth’s climate and ocean currents, according to researchers who recently traced how that mixing happens.

The new study, carried out by the University of Exeter, the University of East Anglia, the University of Southampton, the Woods Hole Oceanographic Institution, the British Antarctic Survey and the Scottish Association for Marine Science, will help inform climate models which until now have lacked the detailed information on ocean mixing needed to provide accurate long-term climate projections. The findings have been published in the journal Nature.

Working in some of the wildest waters on the planet, researchers measured mixing in the Southern Ocean by releasing tiny quantities of an inert chemical tracer into the Southeast Pacific. They tracked the tracer for several years as it went through Drake Passage to observe how quickly the ocean mixed.

The tracer showed almost no vertical mixing in the Pacific but as the water passed over the mountainous ocean floor in the relatively narrow continental gap that forms the Drake Passage it began to mix dramatically.

“A thorough understanding of the process of ocean mixing is crucial to our understanding of the overall climate system,” said Professor Andrew Watson, with the University of Exeter. “Our study indicates that virtually all the mixing in the Southern Ocean occurs in Drake Passage and at a few other undersea mountain locations. Our study will provide climate scientists with the detailed information about the oceans that they currently lack.”

Ocean mixing transfers carbon dioxide from the atmosphere to the deep sea, and ultimately controls the rate at which the ocean takes up carbon dioxide. Over several hundred years this process will remove much of the carbon dioxide that we release into the atmosphere, storing it in the deep ocean. Ocean mixing also affects climate, for example an increase in the rate of deep sea mixing would enable the ocean to transfer more heat towards the poles.

Scientists believe that the lower concentrations of atmospheric carbon dioxide present during the ice ages may have been the result of slower ocean mixing between the surface and the deep sea. Although the reasons for this are not yet clear, this further emphasizes the link between ocean mixing and climate.

 

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