Closing the Loop

The world ocean circulates like a conveyor belt, with cold, salty, dense water in the North Atlantic sinking beneath the surface. But one question remains a mystery: How do these waters eventually gain heat (and buoyancy) to rise back to the surface? A 2015 expedition aboard the Nathaniel B. Palmer led by WHOI scientist Louis St. Laurent and Andreas Thurnherr of Lamont-Doherty Earth Observatory explored the idea that strong currents along canyons on the flanks of mid-ocean ridge cause turbulence that mixes deep waters to shallower depths, closing the loop. Here, Brian Hogue, of WHOI’s Sub-surface Mooring Operations Group (left) helps recover instruments during the cruise.(Photo by Sean P. Whelan, Woods Hole Oceanographic Institution)