Interpreting Regional and Temporal Variability in Global Diapycnal Mixing Inferred from Argo Profiles

Principal Investigator: 
Lynne Talley, Scripps Institution of Oceanography
Caitlin Whalen, Scripps Institution of Oceanography Graduate Program
Proposal Abstract: 

The influence of turbulent ocean mixing transcends its inherently small scales to affect large-scale ocean processes including water-mass transformation, stratification maintenance, and the overturning circulation. However, the distribution of ​diapycnal mixing is not well described by sparse ship-based observations since this mixing is both spatially patchy and temporally intermittent.  Recently, techniques have been developed to infer diapycnal mixing rates from finescale (tens to hundreds of meter vertical scales) shear or strain, using assumptions about the underlying internal wave dynamics that often drive turbulent mixing.  We have begun to apply these techniques to strain measured by the global Argo array.  We have used strain information from Argo float profiles in the upper 2,000 m of the ocean to generate over 400,000 estimates of the turbulent energy dissipation rate, indicative of ocean mixing. While these estimates rely on numerous assumptions, and do not take the place of direct measurement methods, they have been shown to be a good proxy for the distribution of diapycnal mixing. Temporally averaged estimates reveal clear spatial patterns in the parameterized dissipation rate and diffusivity distribution across all the oceans. They corroborate previous observations linking elevated dissipation rates to regions of rough topography. We also observe heightened estimated dissipation rates in areas of high eddy kinetic energy, along the equatorial band, as well as heightened diffusivity in high latitudes where stratification is weak. The seasonal dependence of mixing is observed the Northwest Pacific, suggesting a wind-forced response in the upper ocean.

Start and End Date: 
March 2012 to February 2016