The oceans play a vital role in global warming, for the surface layers of the sea absorb heat and carbon dioxide (CO2) from the atmosphere.

It is essential to know what happens to this warmth and CO2. By knowing the ocean currents, scientists can get an idea as to how swiftly surface warmth will start to heat up lower levels and whether the CO2, absorbed by algae, is sequestered at the ocean bottom or in contrast churned back up to the surface.

The new discovery focuses on the Antarctic Circumpolar Current (ACC), which picks up and cools water that descends from warmer latitudes in the Atlantic, Indian and Pacific oceans.

Scientists led by Alberto Naveira Garabato of the University of Southampton's National Oceanography Centre, southern England, hit on the idea of using a natural plume of helium, disgorged from a submarine volcano in the East Pacific, as a tracer for the ACC.

They found an extraordinary mixing of the ACC in the Southwestern Atlantic at the Scotia Sea, a triangular-shaped area between Tierra del Fuego and the Antarctic peninsula.

The Scotia Sea is notorious for the storms that lash its surface, but what surprised the researchers was the violent twisting of the layers underneath.

The eddy cuts across isopycnals -- layers of the sea that are of different densities -- and effectively acts as a "short circuit" in the ACC. The apparent cause is the rough topography of the sea bed.

The study appears on Thursday in Nature, the weekly British science journal.

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