What Goes Down

A scientific instrument called a CTD (conductivity, temperature, depth) is pulled up to the research vessel Nathaniel B. Palmer from deep in the Atlantic Ocean. The 2015 expedition led by Louis St. Laurent of WHOI and Andreas Thurnherr of Lamont-Doherty Earth Observatory investigated a persistent mystery about ocean circulation: How does cold dense water that sinks to great depths eventually gain heat and buoyancy and rise back to the surface to complete the ocean conveyor belt loop? They explored a theory that strong currents flowing along canyons on the flanks of mid-ocean ridge mountains cause turbulence that mixes deep waters to shallower depths. (Photo by Sean P. Whelan, Woods Hole Oceanographic Institution)