Sammendrag
Oil seeps recently discovered in shallow marine environments offshore W. Svalbard are natural laboratories to study the interactions between hydrocarbons leaks and ecosystems. These environments are often associated with upward fluxes o reduced compounds, i.e. methane and H2S, sustaining chemosynthetic bacterial communities at the seafloor, but it is still unclear the effect on higher organisms and associated biogeochemical processes. Here, we characterized the sediment biogeochemistry at oil seeps at Prins Karl Foreland, using sediment cores collected during CAGE21-1 AKMA expedition in 2021. The pore fluid datasets (SO42-, δ13CDIC, CH4) indicate intense microbial sulfate reduction close to the seafloor associated with methane oxidation. The gas isotopic composition (δ13CCH4, δDCH4, δ13CCO2) of seeping showed a dominant thermogenic component with biodegradation signals, in agreement with the oil geochemistry. Oil-impregnated sediments are characterized by very high C/N ratios (C/N > 50) and depleted δ13CTOC compared to the reference core. The isotopic composition of a seep carbonate concretion found at 4 cm in another push core showed δ13C = -28.6 ‰ and δ18O = 4.9 ‰ in a cavity-filling cement, and δ13C = -26.0 ‰ and δ18O = 4.9 ‰ in micrite. These δ13C values are heavier than typical methane-derived carbonates (
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