Fracture-controlled fluid transport supports microbial methane-oxidizing communities at Vestnesa Ridge
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Published:2019-05-29
Issue:10
Volume:16
Page:2221-2232
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Yao Haoyi, Hong Wei-LiORCID, Panieri GiulianaORCID, Sauer SimoneORCID, Torres Marta E., Lehmann Moritz F., Gründger Friederike, Niemann HelgeORCID
Abstract
Abstract. We report a rare observation of a mini-fracture in near-surface
sediments (30 cm below the seafloor) visualized using a rotational scanning
X-ray of a core recovered from the Lomvi pockmark, Vestnesa Ridge, west of
Svalbard (1200 m water depth). Porewater geochemistry and lipid biomarker
signatures revealed clear differences in the geochemical and biogeochemical
regimes of this core compared with two additional unfractured cores
recovered from pockmark sites at Vestnesa Ridge, which we attribute to
differential methane transport mechanisms. In the sediment core featuring
the shallow mini-fracture at pockmark Lomvi, we observed high concentrations
of both methane and sulfate throughout the core in tandem with moderately
elevated values for total alkalinity, 13C-depleted dissolved inorganic
carbon (DIC), and 13C-depleted lipid biomarkers (diagnostic for the
slow-growing microbial communities mediating the anaerobic oxidation of
methane with sulfate – AOM). In a separate unfractured core, recovered from
the same pockmark about 80 m away from the fractured core, we observed
complete sulfate depletion in the top centimeters of the sediment and much
more pronounced signatures of AOM than in the fractured core. Our data
indicate a gas advection-dominated transport mode in both cores, facilitating
methane migration into sulfate-rich surface sediments. However, the moderate
expression of AOM signals suggest a rather recent onset of gas migration at
the site of the fractured core, while the geochemical evidence for a
well-established AOM community at the second coring site suggest that gas
migration has been going on for a longer period of time. A third core
recovered from another pockmark along the Vestnesa Ridge Lunde pockmark
was dominated by diffusive transport with only weak geochemical and
biogeochemical evidence for AOM. Our study highlights that advective fluid
and gas transport supported by mini-fractures can be important in modulating
methane dynamics in surface sediments.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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