Controls on Benthic Sulfur and Carbon Reservoirs in the Kara Sea: Tracing DMSP and Hydrocarbons across an Ice-Regime Gradient

Arctic shelf seas are important sites for global carbon and sulfur cycling, yet their biogeochemical feedbacks are rapidly changing due to climate change. This study characterizes Dimethylsulfoniopropionate (DMSP) and hydrocarbon signatures in surface sediments (0–1 cm) along a six-station transect in the Kara Sea, from the Yenisey River estuary to Novaya Zemlya (from approx. 71°31' to 77°00' N).

The transect spans a distinct environmental gradient from coastal stations dominated by land-fast ice to open-shelf waters characterized by first-year ice or free from ice. By coupling DMSP concentrations with hydrocarbon biomarkers, we differentiate between terrestrial riverine inputs and autochthonous marine production as drivers of the benthic reservoir. DMSP production is low in riverine regions (~2 nmol g^-1) but higher in all marine regions (40-80 nmol g^-1) with metagenomic analysis suggesting production is primarily from bacteria. Other bacteria contain DMSP catalysis genes encoding proteins converting DMSP to dimethylsulfide (DMS), a global cooling gas. This suggests that production of DMSP and DMS in the Russian Arctic is widespread and large-scale.

Our findings reveal how specific sea-ice regimes and river discharge regulate organic matter provenance and sulfur biochemistry. These baseline data are essential for predicting how Arctic biogeochemical feedbacks — specifically sediment-atmosphere chemical fluxes — will respond to projected declines in sea ice extent and increased river runoff.