Academic journal article The Science Teacher

A New Model of Ocean Circulation

Academic journal article The Science Teacher

A New Model of Ocean Circulation

Article excerpt

The world's oceans act as a massive conveyor, circulating heat, water, and carbon around the planet. This global system plays a key role in climate change, storing and releasing heat throughout the world. To study how this system affects climate, scientists have largely focused on the North Atlantic, a major basin where water sinks, burying carbon and heat deep in the ocean's interior.

But where and how deep waters circulate back to the surface have been a mystery--until now. Recently, scientists have found evidence that the solution to the mystery may lie in the Southern Ocean--the vast ribbon of water encircling Antarctica. The Southern Ocean, according to observations and models, is where strong winds blowing along the Antarctic Circumpolar Current dredge waters up from the depths.

"There's a lot of carbon and heat in the interior ocean," says John Marshall, a professor of oceanography at the Massachusetts Institute of Technology (MIT). "The Southern Ocean is the window by which the interior of the ocean connects to the atmosphere above."

For decades, a conveyor belt model, developed by paleoclimatologist Wallace Broecker, has served as a simple cartoon of ocean circulation. The diagram depicts warm water moving northward--plunging deep into the North Atlantic; coursing south as cold water toward Antarctica; and traveling back north again, where waters rise and warm in the North Pacific.

Evidence has shown, however, that waters rise to the surface not so much in the North Pacific but in the Southern Ocean--a distinction that Marshall and Kevin Speer, a professor of physical oceanography at Florida State University, illustrate in their new schematic for ocean circulation published with an article in Nature Geoscience.

Marshall says winds and eddies along the Southern Ocean drag deep waters--and any buried carbon--to the surface around Antarctica. He and Speer write that the updated diagram "brings the Southern Ocean to the forefront" of the global circulation system, highlighting its role as a powerful climate mediator.

Indeed, Marshall and Speer review evidence that the Southern Ocean may have helped thaw the planet out of the last Ice Age. Though it's unclear what caused Earth to warm initially, this warming may have driven surface wind patterns poleward, pulling up deep water and carbon--which would have been released into the atmosphere, further warming the climate. …

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