Mixing across stable density interfaces in forced stratified turbulence

Understanding how turbulence enhances irreversible scalar mixing in density-stratified fluids is a central problem geophysical fluid dynamics. While isotropic overturning regions are commonly the focus of analyses, we here investigate whether significant may arise anisotropic statically-stable flow. Focusing on single forced direct numerical simulation stratified turbulence, analyze spatial correlations between vertical density gradient $\partial\rho/\partial z$ and dissipation rates kinetic energy $\epsilon$ variance $\chi$, latter quantifying mixing. The domain characterized by relatively well-mixed layers separated sharp stable interfaces that correlated with high shear. static instability most prevalent within mixed layers, much localized to intervening interfaces, phenomenon not apparent if considering local or alone. majority canonical flux coefficient $\Gamma\equiv\chi/\epsilon=0.2$, often assumed ocean parameterizations, extreme values $\chi$ associated elevated $\Gamma$, strongly skew bulk statistics. Our findings suggest current parameterizations turbulent be biased undersampling, such common, but necessarily significant, events overweighted. Having focused it hoped our results motivate broader investigation into role played mixing, across wider range parameters forcing schemes representative turbulence.