Living microbial ecosystems within the active zone of catagenesis; implications for feeding the deep biosphere

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doi: 10.1016/j.epsl.2006.03.040
Author(s): Horsfield, B.; Schenk, H. J.; Zink, K.; Ondrak, R.; Dieckmann, V.; Kallmeyer, J.; Mangelsdorf, Kai; Di Primio, R.; Wilkes, H.; Parkes, R. J.; Fry, J.; Cragg, Barry A.
Author Affiliation(s): Primary:
GeoForschungsZentrum Potsdam, Potsdam, Federal Republic of Germany
Forscungszentrum Jülich, Federal Republic of Germany
Cardiff University, United Kingdom
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 246(1-2), p.55-69. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 65 refs.; illus., incl. sect., 3 tables, geol. sketch map
Summary: Earth's largest reactive carbon pool, marine sedimentary organic matter, becomes increasingly recalcitrant during burial, making it almost inaccessible as a substrate for microorganisms, and thereby limiting metabolic activity in the deep biosphere. Because elevated temperature acting over geological time leads to the massive thermal breakdown of the organic matter into volatiles, including petroleum, the question arises whether microorganisms can directly utilize these maturation products as a substrate. While migrated thermogenic fluids are known to sustain microbial consortia in shallow sediments, an in situ coupling of abiotic generation and microbial utilization has not been demonstrated. Here we show, using a combination of basin modelling, kinetic modelling, geomicrobiology and biogeochemistry, that microorganisms inhabit the active generation zone in the Nankai Trough, offshore Japan. Three sites from ODP Leg 190 have been evaluated, namely 1173, 1174 and 1177, drilled in nearly undeformed Quaternary and Tertiary sedimentary sequences seaward of the Nankai Trough itself. Paleotemperatures were reconstructed based on subsidence profiles, compaction modelling, present-day heat flow, downhole temperature measurements and organic maturity parameters. Today's heat flow distribution can be considered mainly conductive, and is extremely high in places, reaching 180 mW/m2. The kinetic parameters describing total hydrocarbon generation, determined by laboratory pyrolysis experiments, were utilized by the model in order to predict the timing of generation in time and space. The model predicts that the onset of present day generation lies between 300 and 500 m below sea floor (5100-5300 m below mean sea level), depending on well location. In the case of Site 1174, 5-10% conversion has taken place by a present day temperature of ca. 85 °C. Predictions were largely validated by on-site hydrocarbon gas measurements. Viable organisms in the same depth range have been proven using 14C-radiolabelled substrates for methanogenesis, bacterial cell counts and intact phospholipids. Altogether, these results point to an overlap of abiotic thermal degradation reactions going on in the same part of the sedimentary column as where a deep biosphere exists. The organic matter preserved in Nankai Trough sediments is of the type that generates putative feedstocks for microbial activity, namely oxygenated compounds and hydrocarbons. Furthermore, the rates of thermal degradation calculated from the kinetic model closely resemble rates of respiration and electron donor consumption independently measured in other deep biosphere environments. We deduce that abiotically driven degradation reactions have provided substrates for microbial activity in deep sediments at this convergent continental margin. Abstract Copyright (2006) Elsevier, B.V.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Activation energy; Active margins; Aliphatic hydrocarbons; Alkanes; Biochemistry; Biosphere; Burial; Catagenesis; Cenozoic; Deep-sea environment; Degradation; Ecosystems; Genesis; Geomicrobiology; Hydrocarbons; Kerogen; Leg 190; Marine environment; Marine sediments; Methane; Microorganisms; Nankai Trough; North Pacific; Northwest Pacific; Numerical models; ODP Site 1173; ODP Site 1174; ODP Site 1177; Ocean Drilling Program; Organic compounds; Pacific Ocean; Paleotemperature; Quaternary; Respiration; Sediments; Substrates; Tertiary; Thermal alteration; Thermal conductivity; Thermal maturity; West Pacific
Coordinates: N321500 N321500 E1350200 E1350200
N322000 N322100 E1345800 E1345700
N313900 N314000 E1340100 E1340000
Record ID: 2007086960
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands