Using fine-scale measurements in the northwestern Sea of Japan, we estimated the vertical mixing parameters in the sea water column extended from the lower part of the thermocline downward to the near-bottom layer above the continental slope. The vertical scales of the turbulent patches were determined together with the turbulent dissipation rate and diapycnal diffusivity based on the conductivity, temperature, and depth data obtained by an Aqualog moored profiler from April through October 2015. The Thorpe-scale method was used to estimate the vertical mixing parameters as well as the vertical heat and salt fluxes. The enhanced vertical mixing, as well as enhanced upward heat flux and downward salt flux, occurred below the mixed layer despite strong density stratification. By comparing the turbulent dissipation rate and diapycnal diffusivity estimates derived via the Thorpescale method and the estimates of the same parameters obtained earlier by applying the finescale parameterization method to the same dataset in addition to the collocates of the current velocity measurements, the comparative accuracy evaluation of both methods was carried out. Finally, by compiling the vertical mixing data obtained by the Thorpe-scale method and the finescale parameterization approach, the generalized depth profile for the background diapycnal diffusivity is presented for the depth range from 70 to 350 m.

Floating tracer clustering is studied in oceanic flows that combine both a field of coherent mesoscale vortices simulated by a regional, comprehensive, eddy-resolving general circulation model and randomly modeled submesoscale velocity fields. Both fields have rotational and divergent velocity components, and depending on their relative contributions as well as on the local characteristics of the mesoscale vortices, we reported different clustering scenarios. We found that inclusion of the mesoscale vortices does not prevent clustering, but the rates and patterns of clustering become significantly modified. We also demonstrated that even when the surface velocity divergence is weak, it has to be taken into account to avoid significant errors in model predictions of the floating tracer patterns. Our approach combining dynamically constrained and random velocity fields, and the applied diagnostic methods, are proposed as standard tools for analyses and predictions of floating tracer distributions, both in observational data and general circulation models.

The Japan/East Sea is well ventilated and is the most oxygen-rich region in the Pacific. However, quantitative estimates of the turbulent fluxes are missing due to a lack of observational data. To assess turbulent mixing, we employ data from the moored profiler Aqualog survey of April - October 2015 near the northwestern boundary of this region. The survey allowed observation of collocated depth profiles of conductivity, temperature, ocean current, and dissolved oxygen 8 times per day. Based on the finescale parameterization framework, the dissipation rate, the eddy diffusivity and the diapycnal fluxes of heat, salt and oxygen are estimated in the depth range from 130 to 350 m throughout the profiler deployment period. The survey average diffusivity increased with depth from 0.5x10-5 to 4.0x10-5 m2 s-1. The month-to-month variability in the mixing is presented. It was shown that the turbulent mixing undergoes intraseasonal variability. Early in May 2015, a transition in mixing occurred from the winter regime with upward turbulent fluxes of both heat and salt to the summer regime with the downward mixing of heat. The turbulent mixing was elevated in June when large anticyclonic eddies passed the profiler mooring. The probability distributions of the ratios of the turbulent heat and oxygen fluxes to the observed local changes in heat and oxygen were rather stable, particularly in the warm season. The application of the MX Toolbox to the profiler mooring data yields an estimate of the downward oxygen flux of roughly 8.6x103 μmol m-2 month-1. The data analysis was partly performed in the framework of the assignment of FASO Russia (theme 0149-2019-0011) and supported in part by RFBR grant 19-05-00459. The contribution of Dmitry Stepanov in modifying the Mixing Oceanographic Toolbox was supported by RFBR grant 20-05-00083.