Acoustic permafrost and gas seepage through the stability zone of gas hydrates (Laptev Sea)

Arctic subsea permafrost degradation under climate change threatens methane release and destabilises marine ecosystems and infrastructure. Limited field data highlight the urgency of studying permafrost and gas hydrate in the Arctic. This research presents the study of relict subsea permafrost and gas hydrates on the Laptev Sea shelf. Analysis of 149 seismic surveys revealed geophysical indicators of relict subsea permafrost and its patterns. It has been established that relict subsea permafrost sustains extensive gas hydrate stability zone. The hydrate-related reflection near the base of the gas hydrate stability zone was identified at subbottom depths 300–1100 m. The analysis of gas geochemical data allowed identifying zones with increased concentrations of methane and its homologues in bottom sediments. The carbon isotopic composition indicates a mixed origin of methane, both thermogenic and microbial. Anomalously high values of the methane homologues sum (>0.0015 mmol/l) and low values of the Bernard coefficient (<10) are associated with deep gas infiltration indicating degradation of permafrost. Geophysical and geochemical anomalies coincide with the locations of earthquake epicentres and active faults – zones of degradation of subsea permafrost and gas hydrates. The obtained results are crucial for understanding permafrost degradation processes and assessing the potential of gas hydrates on the Laptev Sea shelf.