Biogeochemical evidence of anaerobic methane oxidation on active submarine mud volcanoes on the continental slope of the Canadian Beaufort Sea

Dong-Hun Lee,Alina Stadnitskaia,Young-Gyun Kim,Kyung-Hoon Shin,Jung-Hyun Kim,Young Keun Jin,Yung Mi Lee,Helge Niemann

doi:10.5194/bg-15-7419-2018

Abstract

Abstract. In this study, we report lipid biomarker patterns and phylogenetic identities of key microbial communities mediating anaerobic oxidation of methane (AOM) in active mud volcanoes (MVs) on the continental slope of the Canadian Beaufort Sea. The carbon isotopic compositions (δ13C) of sn-2- and sn-3-hydroxyarchaeol showed the highly 13C-depleted values (−114 ‰ to −82 ‰) associated with a steep depletion in sulfate concentrations within 0.7 m of sediment depths. This suggested the presence of methanotrophic archaea involved in sulfate-dependent AOM, albeit in a small amount. The ratio of sn-2-hydroxyarchaeol to archaeol (> 1) and operational taxonomic units (OTUs) indicated that the anaerobic methanotrophic archaea (ANME) clades ANME-2c and ANME-3 were involved in AOM. Higher δ13C values of archaeol and biphytanes (BPs; -55.2±10.0 ‰ and -39.3±13.0 ‰, respectively) suggested that archaeal communities were also assimilating AOM-derived inorganic carbon. Furthermore, the distinct distribution patterns of methanotrophs in the three MVs appears to be associated with varying intensities of ascending gas fluids. Consequently, our results suggest that the niche diversification of active mud volcanoes has shaped distinct archaeal communities that play important roles in AOM in the Beaufort Sea.

Highlights

Mud volcanoes (MVs) are kilometer-scale, low-temperature, seepage-related geomorphological features that provide some of the most remarkable indications of fluid venting (Ivanov et al, 1998)
In accordance with methane ebullition to water column (Paull et al, 2015), our bulk geochemical data suggest that the contribution of anaerobic oxidation of methane (AOM) biomass to sedimentary total organic carbon (TOC) was rather low at the mud volcanoes (MVs) we investigated, which is in line with our findings that the non-isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) substantially originate from bacterial sources unassociated with methanotrophy
The sharp decrease in pore water sulfate concentrations and steep thermal gradients and previous observations of gas flare above the edifices indicate that sulfate-depleted warm fluids and methane ascend from the Beaufort Sea MVs

Summary

Introduction

Mud volcanoes (MVs) are kilometer-scale, low-temperature, seepage-related geomorphological features that provide some of the most remarkable indications of fluid venting (Ivanov et al, 1998). The roots of MVs can reach depths of up to 20 km (Shnukov et al, 2005); they provide key information about the geological history of the area and its possible hydrocarbon potential (Ivanov et al, 1992, 1998). Eruptions often manifest as a catastrophic emission of fluids consisting of hydrocarbon gases (especially methane), hydrogen sulfide, carbon dioxide, petroleum products, water, and a complex mixture of sediments, so-called “mud breccia” (Akhmanov, 1996; Akhmanov and Woodside, 1998; Ivanov et al.,1998). The occurrence of active MVs could constitute a significant portion of the geological sources of global atmospheric methane emissions (Kopf, 2002; Milkov et al, 2003). In the Arctic Ocean, where the temperature of the bottom water has been increasing (Levitus et al, 2000; Westbrook et al, 2009; Polyakov et al, 2010), concern has been raised that

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