Measuring diapycnal diffusion in the tropical northeastern Atlantic

Abstract

In the upper ocean, turbulence‐driven mixing uses energy to drive water flows across density bands. The rate of this flow, called diapycnal diffusion, is thought to have a strong effect on circulation patterns by mediating the global meridional overturning circulation as well as on the vertical exchange of oxygen. Direct observations of the cross‐density‐band flows, however, are scarce, making accurate representations of the mechanism in circulation models difficult. Starting in 1992, researchers began employing large‐scale tracer experiments to measure the rate of diapycnal diffusion in various ocean basins worldwide. Adding to this collection of experiments, Banyte et al. used a trifluoromethyl sulfur pentafluoride tracer to track ocean circulations in the tropical northeastern Atlantic over a 30‐month period from 2008 to 2010. The authors distributed tracer streaks at a depth of around 330 meters, following a band of consistent density, in their study region south of the Cape Verde Islands. Samples taken 7, 20, and 30 months later allowed them to follow the tracers' dispersion.