Estimation of the seasonal input of freshwater in the Kara sea surface layer using hydrochemical proxies

The Kara Sea receives about 55 % of the total continental runoff to the Siberian Arctic. Water of the Yenisei and Ob Rivers with low salinity (mineralization), flowing into the sea, forms a surface desalinated layer. The desalinated layer spreads over the sea area under the influence of hydrological and meteorological factors. Meltwater generated by the melting of marine and riverine ice and precipitation contribute to the formation of a surface desalinated layer along with continental runoff.

Determining the amount of fresh water is not accurate enough if only the salinity of surface water is considered. It is possible to identify riverine water and meltwater using hydrochemical proxies. The ratio of the major ions in seawater differs from that in riverine and meltwater. River waters are characterized by an increased content of silicate and reduced values of total alkalinity. At the same time, it is possible to identify the waters of the Ob and Yenisei Rivers by the estimated values of the total alkalinity and dissolved inorganic carbon obtained during the research expeditions to the Kara sea from 1993 to 2020.

The calculation of the parts of waters of different origin is done as a result of solving a system of equations. It includes the salinity and alkalinity values of the observed surface waters and those presumably involved in the mixing process. The salinity and alkalinity values of meltwater are taken as 0 and 134 µM respectively.

The total contribution of the Ob and Yenisei runoff ranges from 20 to 90% as it approaches the estuarine areas. The correlation coefficient between the proportion of river water and the salinity of the surface layer is quite high, it is equal to -0.9. This characterizes the inverse linear relationship. The separate contribution of the waters of the Yenisei differs from the contribution of the waters of the Ob, which is related to the hydrological conditions of the rivers.

The contribution of meltwater to the formation of the surface layer of the Kara Sea did not exceed 20%, with the exception of the coastal zone of the Novaya Zemlya. In this coastal zone, meltwater provides the greatest contribution compared to the other sources, which is associated with glacial runoff.

The work is implemented in the framework of the state assignment of the Shirshov Institute of Oceanology RAS (theme No. 0149-2019-0008), with the support of the Russian Scientific Foundation (project № 19-17-00196) and the grant of President of Russian Federation № MK-860.2020.5.