The origin, source, and cycling of methane in deep crystalline rock biosphere

Abstract

The emerging interest in using stable bedrock formations for industrial purposes, e.g., nuclear waste disposal, has increased the need for understanding microbiological and geochemical processes in deep crystalline rock environments, including the carbon cycle. Considering the origin and evolution of life on Earth, these environments may also serve as windows to the past. Various geological, chemical, and biological processes can influence the deep carbon cycle. Conditions of CH4 formation, available substrates and time scales can be drastically different from surface environments. This paper reviews the origin, source, and cycling of methane in deep terrestrial crystalline bedrock with an emphasis on microbiology. In addition to potential formation pathways of CH4, microbial consumption of CH4 is also discussed. Recent studies on the origin of CH4 in continental bedrock environments have shown that the traditional separation of biotic and abiotic CH4 by the isotopic composition can be misleading in substrate-limited environments, such as the deep crystalline bedrock. Despite of similarities between Precambrian continental sites in Fennoscandia, South Africa and North America, where deep methane cycling has been studied, common physicochemical properties which could explain the variation in the amount of CH4 and presence or absence of CH4 cycling microbes were not found. However, based on their preferred carbon metabolism, methanogenic microbes appeared to have similar spatial distribution among the different sites.

Microbial co-occurrence patterns in deep Precambrian bedrock fracture fluids

“…Carbon sources for microbes in deep subsurface are usually in the form of CO 2 , CH 4 or other small hydrocarbons. Abiotic synthesis of organic carbon may take place through Fischer-Tropsch-type reactions and provide a L. Purkamo et al: Microbial co-occurrence patterns photosynthesis-independent carbon source for heterotrophic organisms in deep terrestrial biosphere (Proskurowski et al, 2008;McCollom et al, 2010;Etiope and Sherwood Lollar, 2013;Kietäväinen and Purkamo, 2015). This process may be triggered and enhanced by continuous H 2 flux provided by, for example, serpentinization.…”

Rare Biosphere Archaea Assimilate Acetate in Precambrian Terrestrial Subsurface at 2.2 km Depth

“…These archaea have previously been detected in the Outokumpu deep subsurface as minor groups. Nevertheless, their involvement in the assimilation of acetate and secretion of metabolites derived from acetate indicated an important role in the supporting of the whole community in the deep subsurface, where carbon sources are limited.Geosciences 2018, 8, 418 2 of 20 utilizing soluble gases, such as crustal methane or hydrogen from radiolytic decomposition of water, have been made since [5][6][7][8]. More specifically, the metabolic capabilities of deep terrestrial subsurface microbial communities include the pathways covering, e.g., methanogenesis [9][10][11], anaerobic methane oxidation [12], acetogenesis [4,13], sulfate reduction [14-16], oxidation of sulfur by denitrification [17], and reduction of iron [14].The Outokumpu deep scientific drill hole, located in Eastern Finland, hosts a unique environment piercing through crystalline Precambrian bedrock and its numerous saline fluid filled fracture zones.…”

“…Geosciences 2018, 8, 418 2 of 20 utilizing soluble gases, such as crustal methane or hydrogen from radiolytic decomposition of water, have been made since [5][6][7][8]. More specifically, the metabolic capabilities of deep terrestrial subsurface microbial communities include the pathways covering, e.g., methanogenesis [9][10][11], anaerobic methane oxidation [12], acetogenesis [4,13], sulfate reduction [14-16], oxidation of sulfur by denitrification [17], and reduction of iron [14].…”

Earthquake impact on iron isotope signatures recorded in mineral spring water

“…Some microorganisms can grow in habitats with very low concentrations of organic compounds as long as other energy sources are available [Kietavainen and Purkamo, 2015]. Mineral waters are such a habitat.…”

“…EARTHQUAKES AND FE ISOTOPES IN WATER 8548 activity. Moreover, the activity of the deep subsurface biosphere is increasingly explored, revealing the significance of this habitat for biogeochemical cycles and evidence for deep biosphere activity related to earthquakes [Bräuer et al, 2005;Kietavainen and Purkamo, 2015;Lin et al, 2006;Pedersen, 2000Pedersen, , 2012Schreiber et al, 2012;Sherwood Lollar et al, 2014;Sherwood Lollar et al, 2007].…”