Dr. Yoshinori Takano and Dr. Atsushi Urai, Biogeochemistry Research Center of the Research Institute for Marine Resources Utilization of JAMSTEC(President: Hiroyuki Yamato), identified the molecular species of the main component of the gas (video) that is actively seeping from Lake Suwa, which is a representative fault lake, and clarified its origin, in collaboration with Shinshu University and the Atmosphere and Ocean Research Institute of the University Tokyo.
Lake Suwa is a fault lake located on the Itoigawa-Shizuoka Tectonic Line(ISTL), which itself is located on the boundary between the North American and Eurasian Plates (Fig. 1), with active seeping gas being confirmed at multiple locations in the lake. This “geological hotspot” forms big holes in the midwinter season (Fig. 2), which then influence the lake ice heterogeneity. However, the overall understanding of the biogeochemical cycle, including the main components and origins of these gases and their dynamics after being released into the surface hydrosphere, remain largely unknown.
In the present study, the researchers focused on the molecular species present in the gas and conducted a precise molecular-specific stable carbon isotope ratio/radiocarbon isotope ratio (*1) analysis. These results showed that the main component of seep gas was methane, which originated from deep carbon. These results also involved a quantitative evaluation of the previously-unknown contribution of deep seeping gas and the surface hydrosphere to the carbon cycle; in the future, these are expected to enable the elucidation of the carbon cycle in fault lakes and the food chain in aquatic ecosystems.
This research represents joint research between JAMSTEC and Shinshu University. The results will be published in the specialized academic journal ACS Earth and Space Chemistry, which is published by the American Chemical Society, on June 15 (JST).
【Supplemental information】
Fig.1 Positional relationship between the Itoigawa-Shizuoka Tectonic Line and Median Tectonic Line (top), and an aerial view of Lake Suwa (bottom) (referenced from the Geospatial Information Authority of Japan). Lake Suwa is a fault lake formed on the Itoigawa-Shizuoka Tectonic Line and is located at the intersection with the Median Tectonic Line.
Fig.2 Presence of a big hole that appears in Lake Suwa in midwinter (January 2022). Discharge of fluids from the deep sub-surface has been identified in several locations, and big holes with a diameter of at least 40 m form even when the lake is completely frozen in midwinter.