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Biogeochemical transformations of inorganic nutrients were studied in the mixing zone between the Danube and the north-western Black Sea in July 1995 and in the winter–spring transition period of 1997. Inorganic nutrients, phytoplankton carbon-biomass and biogenic silica were analysed at 10 different locations across the entire salinity gradient in combination with parallel measurements of phytoplankton carbon and inorganic nutrient uptake rates, making use of different tracers (¹⁴C, ¹⁵N, ³²Si and ³²P). The quantitative and qualitative nutrient signature of the Danube outflow into the Black Sea varied seasonally, depending on upwards processes of consumption, remineralization, transformation and elimination. Danube DSi (dissolved silicon) and DIN concentrations decreased from winter to summer, although PO₄ remained constant for the whole season. The winter distribution of inorganic nutrients along the …