Vertical Temperature Stratification of the Gulf of Gdansk Water

The Baltic Sea is characterized by variable hydroacoustic conditions, which depend on hydrological conditions throughout the year. The temperature of the water is the factor that has the greatest impact on the changes in the speed of the sound in this basin. Even at a small depth, we can observe a large temperature gradient affecting the accuracy of the conducted research using hydroacoustic devices. A characteristic feature of the Baltic waters is their layering. In the Baltic Sea, we distinguish three main layers of water: surface, whose temperature is closely related to air temperature and varies within 1-22 degrees during the year, an intermediate characterized by the occurrence of a seasonal thermocline and deep sea temperature, which fluctuates within small limits from 4-6 degrees. There are many factors influencing water temperature changes, among others: heat exchange between water and atmosphere, floods of water with higher salinity from the North Sea, strong winds occurring in the autumn-winter period, an upwelling phenomenon, inflow of fresh waters from rivers. The paper presents the results of research carried out in the Gulf of Gdansk and their impact on the acoustic conditions of the Baltic waters.