The conveyor belt has long served as a metaphor for the movement of ocean currents in the Atlantic Ocean. The belt depicts a continuous loop of southbound subsurface cold water and a northbound flow of warm water on the surface. That loop, part of what is called the Great Ocean Conveyor Belt, has a powerful impact on climate and is taken into account in modeling future climate change.

Oceanographers at Woods Hole Oceanographic Institution (WHOI) and Duke University have found that the southward leg of the loop is not what we thought it was. A WHOI press release says, “Using field observations and computer models, the study shows that much of the southward flow of cold water from the Labrador Sea moves not along the deep western boundary current, but along a previously unknown path in the interior of the North Atlantic.”

On the new path, the cold water is traveling “in the wide-open, turbulent interior of the North Atlantic” and will be much more difficult to study.

The findings were possible because the Northwest Atlantic Fisheries Center in St. Johns, Newfoundland deployed 76 special Range and Fixing of Sound (RAFOS) floats into the current south of the Labrador Sea between 2003 and 2006. The floats drifted at a specific depth for two years, recording location information and temperature and pressure measurements once a day. Only 8 percent of the floats followed the conveyor belt of the deep western boundary current. The researchers also used a modeling program to simulate the launch and dispersal of more than 7,000 virtual “e-floats” from the same starting point. The spread of the e-floats model and the RAFOS float trajectories was very similar.

“This finding means it is going to be more difficult to measure climate signals in the deep ocean,” Susan Lozier of Duke University said. “We thought we could just measure them in the Deep Western Boundary Current, but we really can’t.”

The oceanographers hope to extend their research to study the southward flow of cold water originating even farther north in the Greenland Sea. This research was supported by the National Science Foundation.