Ocean turbulence observations from autonomous profiling floats

Turbulent mixing is the dominant driver in the exchange of oceanic properties across vertical layers and lateral fronts. It shapes the ocean’s stratification dynamics that regulate deep convective processes and water mass exchanges. It also plays an important role in the rate of atmosphere-ocean interactions, and thus is a key factor in our understanding of the dynamics that govern the earth’s climate. Direct measurement of turbulent mixing and associated fluxes of energy, oxygen and nutrients requires measurement of small-scale velocity and/or scalar fluctuations at fast rates. These observations have traditionally been resource-intensive and, consequentially, mostly local and intermittent. Progress is being made on the integration of microstructure turbulence sensors on Argo-class profiling floats, as a novel parameter to measure and from which to derive eddy-diffusivity values for assimilation into ocean and climate models. This is achieved through the integration of rudimentary sensor packages and low-power data loggers. The development includes onboard processing of the otherwise voluminous microstructure data, to make it suitable for satellite transmission. Experiments with two types of such integrations have been done by progressive adopters of the technology. In this presentation results are presented from a turbulence float deployment in the Iceland basin of the North Atlantic, where freshwater-driven deep convection takes place, as well as from deployment of a float in a turbulent eddy of the Kuroshio current.

Targeted deployment of arrays of turbulence floats will result in improved monitoring of regions of the ocean over larger spatiotemporal scales. Results will contribute to the understanding of the mechanistic state and variability in regions of intense mixing, like the Atlantic sub-polar gyre. In addition to presenting scientific results, this presentation will discuss some of the technical requirements for integration of microstructure sensor packages on floats, and proposed methods for data quality, assessment and control.