Purpose. This study aims to identify patterns of spatial variability in the concentrations of key nutrients (nitrite and nitrate, phosphate, and silicate) and carbonate system parameters (pH and total alkalinity) in the bottom waters of the Laptev and East Siberian seas.

Methods and Results. Bottom waters of the Laptev and East Siberian seas were investigated using data collected during the 69th cruise of R/V Akademik Mstislav Keldysh in summer and autumn 2017. Bottom water samples were collected along four transects: Khatanga and Lena (Laptev Sea), and Indigirka and Kolyma (East Siberian Sea). Sampling was performed using the Neimisto corer, which allowed layer-by-layer collection from three horizons (0–15, 15–30, and 30–45 cm) above the seabed. Hydrochemical variables were measured using standard methods. Total alkalinity generally increased from coastal stations toward offshore areas, reflecting the influence of river runoff (1.1–1.9 mM/L), and toward the outer shelf (2.2–2.5 mM/L). Slightly alkaline conditions (pH 7.8–8.1) were observed throughout the study area. The lowest oxygen saturation (56–73 %) occurred in zones directly influenced by large rivers and in areas with limited water exchange. Maximum phosphate (up to 1.43 μM) and silicate (up to 41.22 μM) concentrations at coastal stations confirm the effect of river runoff. Conversely, anomalously high concentrations and nonconservative vertical distributions in some deeper offshore areas may indicate additional sources, including diagenetic processes and inputs associated with submarine permafrost thaw.

Conclusions. The results highlight the key role of the near-bottom layer as an active zone of nutrient transformation, where coupled physical, chemical, and biological processes significantly affect benthic ecosystem functioning. These findings are relevant for assessing climate-change impacts on the Arctic shelf, particularly in the context of submarine permafrost degradation and shifts in river runoff regimes.