Assessment of thermal stratification, stability and characteristics of deep water zone of the southern Caspian Sea

Variations of seawater properties and stratification of water column in the southern deep water zone (470 m depth) of the Caspian Sea were evaluated based on field measured data. Variations of physical characteristics (temperature, salinity, density and sound speed) of seawater mainly were limited to the upper 100 m layers. Below this layer, seasonal changes of seawater parameters were minor. Vertical structure of temperature in the southern Caspian Sea waters was characterized by a significant seasonal thermocline approximately between 20 and 50 m depths in summer with a vertical gradient of around 16 °C. Destruction of the thermocline occurred with the general cooling of the sea surface water and deepening of the mixed layer during late of autumn and winter. Frequency of stability in water column often across the upper layers (surface mixed and thermocline) was more than deeper levels. Variations of salinity were around 12.4 PSU in the time of measurements. Structures of thermocline and pycnocline were characterized by a significant homogeneity especially in offshore stations during the year. According to high agreement between density and temperature in the Caspian Seawater, a strong seasonal pycnocline was observed in the position of the thermocline. Furthermore, structure of sound speed variations followed vertical variations of seawater temperature. Variations of chemical characteristics (dissolved oxygen and pH) of seawater mainly were continued from sea surface to near the sea bed in deep water zone.