RT Journal Article
SR Electronic
T1 Can a red wood-ant nest be a trap for fault-related CH<sub>4</sub> micro-seepage? A case study from continuous short-term <em>in-situ</em> sampling
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 154245
DO 10.1101/154245
A1 G.M. Berberich
A1 A.M. Ellison
A1 M.B. Berberich
A1 A. Grumpe
A1 A. Becker
A1 C. Wohler
YR 2017
UL http://biorxiv.org/content/early/2017/10/10/154245.abstract
AB 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 continuously sampled in-situ and analyzed to detect microbial, thermogenic, and abiotic fault-related micro-seepage. Methane degassing was not synchronized with earth tides. Elevated CH4 concentrations in nest gas appear to result from a combination of microbial activity and fault-related emissions moving via through fault networks through the RWA nest. 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 (microseepage). 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.