Concentration and Diffusion of Nutrients in the Interpore–Bottom Water System of the Ob River Estuary

On cruise 76 in 2019, the R/V Akademik Mstislav Keldysh completed the Gulf of Ob–Kara Sea slope transect. Samples of bottom water and two sediment layers 1 cm thick were obtained with a multicorer. The silicon, mineral and total phosphorus, and organic nitrogen concentrations were measured in them. The magnitude of fluxes of these nutrients at the water–bottom boundary along the transect was calculated; they are all positive, i.e., directed from sediment to water. Comparison of silicon and phosphates fluxes obtained in the transect in 2019 with fluxes measured on a similar transect in 2007 showed good agreement. Silicon fluxes along the transect vary little (less than two times), including the frontal river–sea mixing zone. Mineral phosphorus fluxes have two maxima: in pure river waters and on the slope of the Kara Sea. In the area of the lens of freshened waters, phosphorus fluxes can have an alternating character, depending on season, the state of production, and destructive processes. A method is proposed for comparing fluxes of different nutrients in order to establish the nature of their variability along the transect and to identify measurement errors.