Seasonal variations of vertical structure in the deep waters of the Southern Caspian Sea

Seasonal variations of the vertical structure of the temperature and salinity in the Southern Caspian Sea were studied in this paper. The data were measured in one transect, and 9 stations during winter, spring and summer 2013-2014. Comparison of the estimated mixed layer depth using visual and threshold methods revealed that the threshold method underestimates the mixed layer depth. The depth of the mixed layer reaches its maximum in the winter during cooling and begins decreasing with starting the heating season. The temperature of the mixed layer varied in winter, spring and summer, between 10-12 ˚C, 16.5- 25 ˚C, and 25-25.5 ˚C, respectively. Bellow the mixed layer where the gradient of temperature is large, seasonal thermocline locates between 10-70m. The seasonal thermocline comes up with heating in the spring, and its slope reaches its maximum in the summer as the temperature rises. The temperature and salinity variations inside the deep layer, the deepest layer bellow the thermocline is not significant.