Vertical Variations of the Permanent Halocline on the Eastern Slope of the Gdansk Basin Based on the Results of Autonomous Measurements

At the Atlantic Branch of P.P. Shirshov Institute of Oceanology of the Russian Academy of Sciences, an autonomous thermistor chain was developed and manufactured using a modular design. Measurements conducted on the eastern slope of the Gdańsk Basin (Baltic Sea) revealed fluctuations in isotherms. Interpretation of the permanent halocline oscillations showed that their upward shift is primarily caused by events in which anticyclonic circulation in the water column generates a compensatory current in the bottom layer. This compensatory current, flowing eastward along the southern slope of the Gdańsk Basin, lifts the isotherms near the eastern slope. The highest correlation between the depth of the 5.5 °C isotherm and the projection of the wind stress vector was observed under westerly winds with a slight northerly component, with a time lag of 38–48 hours. This delay is attributed to the system’s inertia. Field measurements were also used to validate the NEMO model data, revealing model inaccuracies: a time lag and smoothing of fluctuations. The most significant discrepancies were observed in the upper part of the temperature sensor string, where the model failed to reproduce high-frequency oscillations. Near the bottom, high-frequency fluctuations diminish, and the model reproduces the vertical movements of the selected isotherm with reasonable accuracy, though still with a delay.