– Coexistence of aerobic and anaerobic methanotrophs is key to methane consumption –
Researchers) MIYAJIMA Yusuke, Researcher, YOSHIOKA Hideyoshi, Group Leader, Research Institute for Geo-Resources and Environment
SUZUMURA Masahiro, Attached to Research Institute, AOYAGI Tomo, Senior Researcher, HORI Tomoyuki, Chief Senior Researcher, Environmental Management Research Institute
- Evaluation of vertical distribution and activity of microorganisms in marine sediments off Sakata City, Yamagata Prefecture, Japan
- Discovery of a coexisting zone of aerobic and anaerobic methanotrophs and estimation of methane consumption rates in sediments including this zone
- Contribution to understanding methane dynamics in the seafloor and assessing the environmental impact of methane hydrate development
Methane consumption rate was estimated by geochemical and microbiological analyses and incubation experiments of subseafloor sediments.
*Figure modified from Miyajima et al. (2024)
Methane is a greenhouse gas and a major component of natural gases, and understanding its formation and consumption processes is important for the sustainable utilization of methane reserves. Methane produced deeply below the seafloor remains partly in sediments as natural gases and methane hydrates, but it also rises through pore spaces in the sediments and faults and is released from the seafloor into the seawater. Although the ocean covers 70 % of the Earth's surface area, the amount of methane released from the seafloor to the ocean and the atmosphere is less than several percent of the total global release. Microorganisms living in sediments near the seafloor play an important role in consuming methane and reducing its release from the seafloor. However, the activity and distribution of these methanotrophs in sediments and their methane consumption rates are poorly quantified. This study used an interdisciplinary approach, combining geochemistry and environmental microbiology, to understand the microbial methane consumption process in deep-sea sediments.
In 2020, AIST researchers estimated the microbially mediated methane consumption rate by chemical and microbiological analyses coupled with stable isotope tracer experiments of sediments collected from the seafloor off Sakata City, Yamagata Prefecture, where methane hydrates are distributed. They also discovered that in the redox transition zone below the seafloor, methane-oxidizing microorganisms that require oxygen for growth (aerobic methanotrophs) and those that do not (anaerobic methanotrophs) are metabolically active and consume methane. These findings contribute to an accurate understanding of the seafloor budget of methane.