Origin of freshwater component in estuaries of the Ob and Yenisei Rivers and waters of Kara Sea adjacent zones based on isotopic (δD, δ18O) data

Methods of estimation the isotopic parameters (δD, δ18O) of the freshwater component in the river-sea transition zone are considered in this work. This research is based on samples collected at the end of the summer season along two meridional sections laying from the estuaries of the Ob and Yenisei rivers to the center of the Kara Sea. The runoff of these rivers has contrasting isotopic parameters contrasting (δ18O = –15.0 ± 0.3‰, δD = –112.7 ± 2.1‰ for the Ob and δ18O = –18.9 ± 0.6‰, δD = –142.2 ± 4.3‰ for the Yenisei). It has been established that river waters located within the surface layer of sea water do not have time to homogenize: in the center of the Ob-Yenisei plume, the part of Ob waters is 60%. Within river estuaries, FC is homogeneous only in the upper layer of water (less than 5 m); with depth, variations in δ18O(FC) values reach 16‰ for the Ob Bay and 12‰ for the Yenisei Bay, exceeding the annual course of seasonal variations of this value in river water. In the bottom layer for the estuarine zones of both rivers, the presence of a total FC with light isotopic characteristics corresponding to regional atmospheric precipitation is observed, that FC is supplied to the estuary zone with the waters of the Kara Sea.