Measuring diapycnal diffusion in the tropical northeastern Atlantic


  • Colin Schultz


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.