Spatiotemporal Variability and Transformation of Nutrients in the Gulf of Ob after Seasonal Ice Melt

We have investigated the spatiotemporal variability of the nutrients (P, Si, N) concentrations in the northern part of the Gulf of Ob, where the fresh–sea waters mixing zone is located. The data were obtained in July 2016 and 2019. These years differed significantly: in 2016 we found warm (up to 14°C) and oxygenated (up to 130%) waters, while in 2019 the temperature did not exceed 8°C, and oxygen saturation was about 90%. Differences were observed in the content of dissolved silicon and forms of nitrogen, their concentrations were higher in 2019. Significant differences in the content of nutrients in water in the studied years from the mean annual values were revealed. Possible factors governing these differences are the seasonal variability and heterogeneity of river runoff, as well as the time of ice retreat off the water area of the Gulf, which affects the production and destruction characteristics of the water area.