Vertical turbulent fluxes from NEMO

Is it possible to output vertical fluxes of heat, density and salinity (calculated in NEMO) to NetCDF output files?

It depends what you mean, but you can output trends in vertical diffusion of T or S. Check trdtra.F90.

I mean flux variables, which is calculated as follows:
flux_t = - avt * grad_t
flux_s = -avs * grad_s,
where avt, avs - vertical coefficients,
grad_t, grad_s - vertical gradients of temperature and salinity

From trdtra.F90 it seems that ttrd_evd and strd_evd are the flux variables I need.
Am I correct?

The trends in trdtra are the time variation of the process for T & S, which equals the divergence of fluxes for a given grid cell. But if you start from the bottom grid cell upward I guess you can deduct the fluxes as you define them
Then which variable you need is a big question, it depends a bit what you want to include or not. ttrd_zdf
seems the obvious choice, but it is not purely vertical. ttrd_zdfp is better I guess. ttrd_evd is for convection (when N2 becomes negative), so not related with avt/avs computed by the vertical turbulence model.