Preprints
https://doi.org/10.5194/egusphere-2025-4756
https://doi.org/10.5194/egusphere-2025-4756
06 Oct 2025
 | 06 Oct 2025
Status: this preprint is open for discussion and under review for Biogeosciences (BG).

Methane releases across the Laptev Sea signaled by time-integrated biomarkers of aerobic methane oxidation

Albin Eriksson, Birgit Wild, Wei-Li Hong, Henry Holmstrand, Francisco Jardim de Almada Nascimento, Stefano Bonaglia, Denis Kosmach, Igor Semiletov, Natalia Shakhova, and Örjan Gustafsson

Abstract. Elevated methane concentrations in seawater have been reported over extensive areas of the East Siberian Arctic Seas, overlying thawing subsea permafrost. However, observed methane concentrations of the ephemeral seawater are highly variable across both space and time, compromised by both the timing of rare measurements and storm-driven exchanges to the atmosphere. Here, we applied time-integrated signals of the δ13C-composition of specific C30 hopanoids (diploptene, hop-17(21)-ene, neohop-13(18)-ene and diplopterol) in surface sediments to trace aerobic methane oxidation and thereby provide a proxy for methane release. Interpretations of hopanoids and possible sources were further assessed by 16S-rRNA analyses in the surface sediments. The consistently low δ13C-C30 hopenes signals, ranging between −57.5 to −37.1 ‰ (n=23) across the Laptev Sea shelf indicated aerobic methane oxidation. This suggests ubiquitous methane release with the most pronounced intensities in the outer shelf region, broadly consistent with the observed methane concentrations. Notably, depleted δ13C-C30 hopenes were also found in the mid-shelf region of the Laptev Sea, earlier thought to be an area of comparatively low methane emissions. High methane concentrations were also observed in the vicinity of the Lena River delta, yet the isotopically heavier δ13C-C30 hopenes may here reflect a combination of lower aerobic methane oxidation, a greater relative abundance of type II methanotrophs (lower isotope fractionation during hopanoid production) and isotope dilution from non-methanotrophic sources. While this complicates the biomarker interpretation in the unique setting near the Lena River delta, the δ13C-C30 hopenes were still much lower than δ13C-OC, indicating aerobic methane oxidation and a clear methane release signal also in this regime. Taken together, the results unravel the wider cross-shelf patterns of methane releases in the Laptev Sea through probing of methane fossilised in membrane lipids of aerobic methanotrophs with the molecular-isotopic pattern being preserved in the sedimentary archive.

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Albin Eriksson, Birgit Wild, Wei-Li Hong, Henry Holmstrand, Francisco Jardim de Almada Nascimento, Stefano Bonaglia, Denis Kosmach, Igor Semiletov, Natalia Shakhova, and Örjan Gustafsson

Status: open (until 17 Nov 2025)

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Albin Eriksson, Birgit Wild, Wei-Li Hong, Henry Holmstrand, Francisco Jardim de Almada Nascimento, Stefano Bonaglia, Denis Kosmach, Igor Semiletov, Natalia Shakhova, and Örjan Gustafsson
Albin Eriksson, Birgit Wild, Wei-Li Hong, Henry Holmstrand, Francisco Jardim de Almada Nascimento, Stefano Bonaglia, Denis Kosmach, Igor Semiletov, Natalia Shakhova, and Örjan Gustafsson
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Latest update: 06 Oct 2025
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Short summary
Thawing subsea permafrost in the East Siberian Arctic Seas releases methane, a potent greenhouse gas. Using molecular fossils in sediments, we traced past methane oxidation to reveal widespread methane release across the Laptev Sea, including regions once thought low in emissions. This approach captures long-term patterns, overcoming limits of short-term seawater measurements and highlights the importance of the Laptev Sea in Arctic methane cycling.
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