MicroRiYo: An Observing System for Deep Repeated Profiles of Kinetic Energy Dissipation Rates from Shear-Microstructure Turbulence along a Mooring Line

Abstract A new observing system that provides deep repeated profiles of the oceanic kinetic energy dissipation rate and small-scale mixing is presented. The system is designed to provide 300 dissipation rate profiles using a vehicle that cycles along a mooring line from the subsurface down to a maximum depth of 4000 m. The system was tested for 2 weeks between 630 and 1700 m during a cruise that took place on the Lucky Strike segment of the Mid-Atlantic Ridge. The vehicle collected 35 profiles at a mean downcast velocity of 0.63 m s −1 . To quantify the quality of the measurements, profiles from the mooring are compared with nearby profiles from an autonomous microstructure free-falling instrument. The dissipation rate noise level varies between O (10 −10 ) and O (10 −9 ) W kg −1 . This noise level is low enough to detect turbulent patches at depth. The largest dissipation rate measured at this site was O (10 −7 ) W kg −1 . Significance Statement Understanding how the ocean dissipates the energy it receives from astronomical and atmospheric forcing (tides, heat, freshwater, wind) is a key element of ocean dynamics. Here, we present a new observing system that allows repeated measurements of the dissipation of kinetic energy in the ocean from the subsurface down to 4000 m at a given geographical point. Three hundred profiles can be measured, providing insights into the dynamics responsible for energy dissipation and tracer mixing. This observing system is particularly suited to the deep open ocean, where such observations remain scarce.