Towed-chain measurements of conductivity microstructure in the Sargasso Sea are reported for a 15-m aperture of high-frequency conductivity sensors and thermistors. Since the conductivity sensors are dc capable, co-located with thermistors, and nearly immune to biologic fouling, we are able to compute the density ratio, Rρ, from salinity and temperature gradients as the chain crosses isopycnal surfaces. Observations are made of numerous microstructure patches that are shown to be active salt-fingering and others that are not associated with double-diffusion. Three tows (duration of about 20 h) within varying environments described as Deep-Homogeneous, Shallow-Homogeneous, and Frontal have been analyzed to describe the characteristics of the microstructure and its relation to the temperature-salinity finestructure and in particular Rρ. Hypothesis testing for the dependence of microstructure on Rρ shows that the hypothesis “microstructure is independent of Rρ” fails for the three environments. The volume fractions of the tows containing microstructure, identified by a zero-crossing algorithm, are 7%, 14%, and 14% for the Deep, Shallow, and Frontal environments, respectively. Double-diffusion accounts for 27%, 11%, and 35% of this microstructure, respectively. Conductivity gradient spectra of microstructure within the supercritical salt-finger regime (1 < Rρ < 2) follows a nearly k2 behavior for wavenumbers between 1 and 10 cpm and peak typically between 10 and 20 cpm, similar to the observations of Gargett and Schmitt and those of Marmorino.

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