Near-surface hydrocarbon anomalies in shelf sediments off Spitsbergen: Evidences for past seepages

As global warming occurs, the dissociation of bound methane on Arctic shelves due to ocean current temperature changes may become a major contributor to the global methane budget, and thus contribute to strong positive climate feedback mechanisms. However, little is known about the magnitude and fate of methane emissions from shallow submarine sediments to the atmosphere in the peculiar area. In this paper, we present one of the first direct evidences for seepage on the northwestern Barents Sea shelf. By studying the molecular and isotopic signatures of low‐molecular‐weight hydrocarbons in seawater, near‐surface sediment pore space and the sediment matrix at 26 locations, we provide a detailed view on the partitioning of gaseous hydrocarbons in the sediment‐water interface off Spitsbergen. In the free gas phase, low concentration of methane (∼28 ng/g wet Sediment) paired with constantly high isotopic values (∼−65‰) is consistent with high impact of methane oxidation on the isotopic composition. In contrast, high concentrations of adsorbed CH4 (up to 5292 ng/g wet