Spectral analysis and interpretation of salinity-temperature-depth records

In the Gulf of Alaska, the winter profiles of temperature and salinity against depth show considerable fine structure, the features of which are most pronounced in the pycnocline. Regarding the observed profiles as consisting of a mean profile and a perturbation profile, we can compute the wave number spectrum of the perturbations. The temperature spectrum shows a single significant peak at 17 cycles per kilometer. The salinity spectrum has a peak at 20 cycles per kilometer and differs from the temperature spectrum at high wave numbers. Temperature and salinity perturbations are directly related to each other in a narrow band of wave numbers centered around 20 cycles per kilometer; elsewhere, they are unrelated. The dominant wavelength of the temperature perturbations is 60 meters and of salinity perturbations, 50 meters. The Vaisala frequency is a very complicated function of depth and has a maximum, 0.016 sec−1, in the halocline. It is a useful measure of the stability oscillations only if the vertical displacements are less than about a meter.