Seasonal and Spatial Variations of the Water PhysicalProperties in Alashtrood and Lavijrood Regions

The vertical structures of the temperature, salinity and density are studied based on the measured data during fall, spring and summer 2016-2017 in Alashtrood and Lavijrood regions in the Southern Caspian Sea of Mazandaran. The results show a dominant role of the temperature in density determination. This can be attributed to the small range of salinity variations encountered in the studied regions. This can also be explained based on the fact that the temperature is the dominant factor to determine the density in tropical and subtropical regions. However, the role of the salinity is still important and cannot be ignored. Despite the similarity between the vertical structures of temperature in both regions during the fall, different vertical structures of the salinity have led to different structures for the density. During the spring in Lavijrood area, intrusion of the warm and fresh water at distance of 4-8 km from the coast, has led to a shallow mixed layer depth. The mixed layer depth has its maximum and minimum values during the fall and spring, respectively. Despite the fact that during the summer, the shallowest mixed layer depth is expected due to the strong stratification, we witnessed a deeper mixed layer depth in this season comparing with the spring profiles. This result is because of the high evaporation rate causing an increase in the surface salinity, which results in higher convection and consequently a deeper mixed layer. Finally, it is found that the vertical structures of the physical properties are comparable in both transects during the summer.