In the Southern Ocean, a massive water conveyor belt—the Antarctic Circumpolar Current (ACC)—encircles Antarctica. The ACC is of special interest to researchers who are trying to quantify the Southern Ocean’s contribution to global climate.

In a new paper, Firing et al. examine the movement and circulation of the ACC in the Drake Passage, the span of water between the southernmost tip of South America and the South Shetland Islands of Antarctica. The Drake Passage constricts the ACC into a narrow region, which makes it one of the best places for scientists to study the current.

The researchers looked at data collected by an array of instruments that measured water velocity through the Drake Passage from the surface of the ocean to the seafloor. The researchers found that bottom currents are strongly influenced by seafloor topography, especially where strong flow encounters steep inclines. At such topographic features, sharp changes in pressure can produce a rotational force—called bottom pressure torque—which acts to steer the current.

From the collected data, the researchers estimated this force and its influence on the ACC. They discovered that this bottom pressure torque in Drake Passage had an effect more than 10 times larger than the average effect of wind blowing over the ACC at the surface.

As the Southern Ocean responds to climate changes, including increased winds, scientists will continue to study the changing structure of the ACC. (Journal of Geophysical Research: Oceans, doi:10.1002/2016JC011682, 2016)

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