A study of the Ob-Yenisei plume structure conducted with the support of SCANEX Group
According to the authors, the Kara Sea receives large river runoff (1,350 - 1,500 km³, mainly from the Ob and Yenisei rivers), which accounts for one quarter of total river discharge to the Arctic Ocean. It results in formation of the Ob-Yenisei plume with the area of 200,000 – 250,000 km² during ice-free period, which is among the largest river plumes in the World Ocean.
These river plumes have been explicitly studied before during the warm period in summer and early autumn. However, this study reports in situ measurements performed in the Kara Sea in late October in 2020, 2021, and 2022. Such data help to identify the vertical structure of the plume shortly before ice formation. The study describes processes, which determine vertical structure of the plume during late autumn and precondition its buoyancy-driven dynamics in the ice-covered Kara Sea.
The researchers reveal that intense convection occurs in the Ob-Yenisei plume due to heat loss from the surface layer, which is caused by transport of cold air from land to the central part of the Kara Sea. In situ measurements performed in the Kara Sea in late October demonstrated significant differences in vertical thermohaline structure of the Ob-Yenisei plume as compared to its state in August - September. The most prominent feature of the Ob-Yenisei plume, which is regularly observed in late October, is a very narrow and sharp vertical gradient zone between the plume and the subjacent saline sea. In particular, at certain areas of the plume-sea interface, salinity increased from 16 - 18 to 28 - 30 at vertical distance of 1 - 2 m, which is among the largest vertical salinity gradients measured in the World Ocean.
This sharp gradient is not formed at the whole area of the plume except, first, at the Ob and Yenisei gulfs due to low surface salinities and the related high temperatures of maximal density and, second, at the lateral boundary of the plume due to intense horizontal mixing across the plume-sea border. As a result, autumn convection significantly modifies vertical structure of the Ob-Yenisei plume that could affect its further spreading below sea ice during winter season.
The complete translation of this article, which details the process of the study and findings of the researchers, can be found here.