title: Subduction zone forearc serpentinites as incubators for deep microbial life.
abstract: Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ∼10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth's largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth's history such as the late heavy bombardment and global mass extinctions.
authors.affiliation: Department of Earth Sciences, Utrecht University, 3584 CD Utrecht, The Netherlands; o.plumper@uu.nl.
authors.forename: Oliver
authors.initials: O
authors.lastname: Plümper
authors.affiliation: Department of Earth Sciences, Utrecht University, 3584 CD Utrecht, The Netherlands.
authors.forename: Helen E
authors.identifier: 0000-0002-1825-782X
authors.initials: HE
authors.lastname: King
authors.affiliation: Steinmann Institut für Geologie, Mineralogie und Paläontologie, University of Bonn, 53115 Bonn, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Geisler
authors.affiliation: Department of Earth Sciences, Utrecht University, 3584 CD Utrecht, The Netherlands.|Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: BHP Billiton Western Australia Iron Ore, Perth, WA 6000, Australia.
authors.forename: Sonja
authors.initials: S
authors.lastname: Pabst
authors.affiliation: Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Ivan P
authors.initials: IP
authors.lastname: Savov
authors.affiliation: Department of Physics, University of Auckland, Auckland 1010, New Zealand.
authors.forename: Detlef
authors.initials: D
authors.lastname: Rost
authors.affiliation: Department of Earth Sciences, University of Gothenburg, 40530 Gothenburg, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Zack
mesh_terms: D017753:Ecosystem; D009930:Organic Chemicals / Q000737:chemistry; D010140:Pacific Ocean; D012623:Seawater / Q000032:analysis* / Q000382:microbiology; D018707:Volcanic Eruptions / Q000032:analysis*
chemical_list: D009930:Organic Chemicals
keywords: deep biosphere; forearc; serpentinization; subduction zone