TY - JOUR T1 - Red wood-ant nests are traps for fault-related CH<sub>4</sub> micro-seepage JF - bioRxiv DO - 10.1101/154245 SP - 154245 AU - G.M. Berberich AU - A.M. Ellison AU - J. Hartmann AU - M.B. Berberich AU - A. Grumpe AU - A. Becker AU - C. Wöhler Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/06/23/154245.abstract N2 - Methane (CH4) is common on Earth, forms the major commercial natural gas reservoirs, and is a key component of the global carbon cycle, but its natural sources are not well-characterized. We present a geochemical dataset acquired from a red wood-ant (RWA; Formica polyctena) nest in the Neuwied Basin, a part of the East Eifel Volcanic Field (EEVF), focusing on methane (CH4), stable carbon isotope of methane (δ13C-CH4), RWA activity patterns, earthquakes, and earth tides. Nest gas and ambient air were analyzed to detect microbial, thermogenic, and abiotic fault-related micro-seepage. Neither methane degassing nor RWA activity was synchronized with earth tides. Two δ13C-CH4 signatures were identified in nest gas: -69‰ and -37‰. The -69‰ signature of δ13C-CH4 within the RWA nest is attributed to microbial decomposition of organic matter. This finding supports previous findings that RWA nests are hot-spots of microbial CH4. Additionally, the -37‰ δ13C-CH4 signature is the first evidence that RWA nests also serve as traps for fault-related emissions of CH4. The -37‰ δ13C-CH4 signature can be attributed either to thermogenic/fault-related or to abiotic/fault-related CH4 formation originating from e.g. low-temperature gas-water-rock reactions in a continental setting at shallow depths (micro-seepage). Sources of these micro-seeps could be Devonian schists (“Sphaerosiderith Schiefer”) with iron concretions (“Eisengallen”), sandstones, or the iron-bearing “Klerf Schichten”. We cannot exclude overlapping micro-seepage of magmatic CH4 from the Eifel plume. Given the abundance of RWA nests on the landscape, their role as sources of microbial CH4 and traps for abiotically-derived CH4 should be included in estimation of methane emissions that are contributing to climatic change. ER -