A descriptive analysis of the linkage between the vertical stratification and current oscillations in the Gulf of Finland

The data from five ADCP deployments with duration from one to several months in various locations of the Gulf of Finland were analyzed. The observations revealed that the shear maxima of current velocity were strongly linked to the pycnoclines — the seasonal thermocline or vertical salinity gradient. The shear maxima were not detected when the quasi-permanent halocline temporarily vanished in winter due to strong SW winds causing reversed estuarine circulation in the gulf. The kinetic energy spectra of currents revealed the energy maxima at a broad semi-diurnal frequency band, broad diurnal frequency band, and low-frequency seiches band. In the periods of strong wind forcing and weak stratification, the current oscillations coincided with different modes of seiches. During the periods of the two- or three-layer flow in summer, the inertial oscillations were dominating in the upper layer while seiches could be more prominent either in the upper layer or the halocline.