Estimating salinity variance dissipation rate from conductivity microstructure measurements

At the smallest length scales, conductivity measurements include a contribu tion from salinity fluctuations in the inertial-convective and viscous-diff usive ranges of the turbulent scalar variance spectrum. Interpreting these measurements is complicated because conductivity is a compound quantity of both temperature and salinity. Accurate estimates of the dissipation rate o f salinity variance chi(S) and temperature variance chi(T) from conductivit y gradient spectra Psi C-z(k) require an understanding of the temperature-s alinity gradient cross spectrum Psi(SzTz)(k), which is bounded by \Psi(SzTz )\ less than or equal to root Psi(Sz)Psi(Tz). Highly resolved conductivity measurements were made using a four-point cond uctivity probe mounted on the loosely tethered vertical profiler Chameleon during cruises in 1991 and 1992. Thirty-eight turbulent patches were select ed for homogeneity in shear, temperature gradient, and salinity gradient fl uctuations and for clear relationship between temperature and salinity. Est imates of chi(T) and chi(S) from the conductivity probe are found to agree with independent estimators from a conventional thermistor probe.