Mixing in a coastal environment: 2. A view from microstructure measurements

Abstract

[1] During the Coastal Mixing and Optics Experiment in 1996 and 1997, an integrated dye and microstructure experiment was done to measure and compare mixing rates on the continental shelf. The results of the dye experiment are presented in the companion paper by Ledwell et al. [2004]. In this paper, we explore the results from microstructure measurements using a vertical profiling instrument. We measure temperature and velocity microstructure and, along with simultaneous measurements of salinity and temperature as well as a shipboard acoustic Doppler current profiler (ADCP), are able to estimate the vertical diffusivities of heat, mass, and momentum. In three of four dye injections performed, we were able to make a comparison of the diffusivity from both dye and microstructure measurements. Although the mixing rates were quite small (vertical diffusivity of heat,

Nutrient supply controls picoplankton community structure during three contrasting seasons in the northwestern Mediterranean Sea

“…The data processing was carried out with the commercial software MSSpro, which included the removal of spiky data as described in detail in Mouriño-Carballido et al (2011). Vertical diffusivity (Kz) was estimated as: (2) where e is the mixing efficiency, here considered as 0.2 (Osborn 1980), as supported by the comparison of Table 1 microstructure measurements and tracer release experiments both in the open ocean and coastal waters (Ledwell et al 2000, Oakey & Greenan 2004, Gregg et al 2012. Vertical diffusive fluxes of nitrate were calculated following the Fick's law, from the product of the nitrate gradient across the nitracline and the averaged Kz for the same depth interval (Sharples et al 2001, Fernández-Castro et al 2015.…”

Mixing efficiency in natural flows

“…In addition, γ o , which is equivalent to γ mf , was evaluated (table 1) using independent measurements of B and P, and the results are approximated in figure 7 as .1) for the nocturnal stably stratified atmospheric boundary layer is in good agreement with many previous estimates of γ for natural waters. In ocean mixing studies, γ = 0.2 is frequently used [4,14,54,[56][57][58][59][60][61][62][63]; however, higher (up to 0.4) and lower (approx. 0.1) values of γ have also been suggested (e.g.…”

Geostrophic Adjustment of an Isolated Diapycnal Mixing Event and Its Implications for Small-Scale Lateral Dispersion

“…Temperature and velocity microstructure measurements taken during CMO (Oakey and Greenan 2004;Sundermeyer et al 2005) showed the presence of patchy regions of intense mixing superimposed on a relatively quiescent background of low diapycnal diffusivities. It is speculated that these well-mixed regions represent the end state of random, localized wave breaking or shear instability events.…”