Structure of the Freshened Surface Layer in the Kara Sea During Ice-Free Periods

This work is focused on the seasonal and interannual variability of the freshened surface layer (FSL) in the Kara Sea during ice-free periods. The majority of annual freshwater runoff inflows to the Kara Sea during the freshet period in June-July. As a result, a large low-salinity and strongly stratified FSL is formed in the central Kara Sea at the beginning of the ice-free period. Initially, this layer is fresh with salinities of less than 15. Then, in August-October, river discharge steadily decreases, the fresh (<15) and strongly stratified river plume remains limited to the inner part of the FSL adjacent to the Ob and Yenisei gulfs, which receives reduced freshwater discharge. The area of the fresh plume steadily decreases with decreasing of river discharge; in October, it remains only within the Ob and Yenisei gulfs. Area and position of the outer part of the FSL, on the opposite, remain stable until the end of ice-free period. Salinities in the outer part steadily increase to 20-25, vertical salinity gradients at the boundary with the subjacent sea decrease, albeit remain prominent. Area and position of the FSL also have low interannual variability, because the volume of river runoff during freshet period in June-July is stable on interannual time scale. As a result, downward freshwater transport and the formation of the seasonal halocline occur in August-October at the stable area located in the central Kara Sea.