Biogeochemical signatures for archaeal communities involved in active gas seeping on Tatarsky Trough

The Tatarsky Trough lies near the eastern coast of the Far Eastern Russia, extending into the northern parts of the East Sea of Korea (also known as the Sea of Japan). This region is renowned for its tectonic activity and active gas seeps, making it an ideal natural laboratory for studying the biogeochemical dynamics of gas-rich sediments. In this study, we investigated two sediment cores, LV67-07HC (358 cm core length) and LV67-19HC (398 cm core length), recovered from active fault zones on the eastern slope (water depths of 300–700 m) during the SSGH expedition aboard the R/V Akademik M. A. Lavrentyev in 2014. Using a combination of lipid and nucleic acid analyses alongside other parameters (i.e., gas and porewater composition), we aim to assess the potential environmental roles of archaeal communities inhabiting these seepages. Both cores exhibited high abundances of lighter hydrocarbon gases, primarily methane and carbon dioxide. The sulfate-methane transition zone (SMTZ) was clearly delimited, with its depth varying based on the extent of deep fluid ascent within coal-gas areas. Notably, significant concentrations of ¹³C-depleted archaeal lipids - glycerol dialkyl diethers (DGDs) and glycerol dialkyl glycerol tetraethers (GDGTs) - were observed near dense carbonate concretions in core LV67-07HC (91–185 cm depth). This finding suggests sustained methanotrophic activity associated with gas seepage events in the Tatarsky Trough. In these settings, archaeal sequences predominantly revealed the presence of ANME-1 clades, which are known to thrive under intense seepage conditions within coal-gas zones. Considering that gas hydrate destabilization in the Tatarsky Trough could trigger slope failures, a notable geological hazard, our results offer valuable insights into the transport and removal processes of hydrocarbon gases, aiding in the evaluation of their impact on regional carbon cycling.