Biogeochemistry of methane in Arctic waters: A multiyear synthesis (2014–2022) from the North Atlantic-Arctic sector and Barents Sea

Abstract. Methane seeping from numerous point sources at the seabed represents a biogeochemically constrained carbon source in the water column of the Arctic Ocean. Here, we compile and synthesise water-column data from 28 research cruises conducted between 2014 and 2022 to evaluate the spatial distribution and variability of methane across Arctic seep systems and to assess whether methane enrichment produces detectable changes in water-column biogeochemistry. Our synthesis shows that methane concentrations span five orders of magnitude, ranging from non-detectable levels (<0.52 nM) to 10⁵ nM. Despite this distinct variability, continuous seeping of methane does not measurably alter bulk nutrient regimes, but it influences organic matter cycling through microbial methane oxidation (MOx). In contrast, nutrient and carbon biogeochemistry appear closely associated with seasonal patterns in primary production, showing typical vertical profiles, even in regions of maximum methane flux. This reflects the relatively low abundance of methane compared to other substrates, as nutrients and dissolved organic carbon concentrations remain one to two orders of magnitude higher even at peak methane levels. Consequently, methane-derived carbon constitutes only a minor fraction of total biogeochemical pools, constraining its effect on nutrient dynamics. However, methane exerts a cumulative influence by altering microbial processes and carbon transformation pathways, even in the absence of detectable changes in bulk nutrient concentrations.