A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling.

Luo, Min, Dale, Andrew W. , Haffert, Laura, Haeckel, Matthias , Koch, Stephanie, Crutchley, Gareth, De Stigter, Henko, Chen, Duofu and Greinert, Jens (2016) A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling. Open Access Geochemistry, Geophysics, Geosystems, 17 (12). pp. 4817-4835. DOI 10.1002/2016GC006643.

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Abstract

Takahe seep, located on the Opouawe Bank, Hikurangi Margin, is characterized by a well-defined subsurface seismic chimney structure ca. 80,500 m2 in area. Sub-seafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure. Reaction-transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m. Model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas. The dissolution of gas (up to 3761 mmol m−2 yr−1) dwarfed the rate of methanogenesis within the simulated sediment column (2.6 mmol m−2 yr−1). Dissolved methane is mainly consumed by anaerobic oxidation of methane (AOM) at the base of the sulfate reduction zone and trapped by methane hydrate formation below it, with maximum rates in the central part of the chimney (946 and 2420 mmol m−2 yr−1, respectively). A seep-wide methane budget was constrained by combining the biogeochemical model results with geophysical data and led to estimates of AOM rates, gas hydrate formation and benthic dissolved methane fluxes of 3.68 × 104 mol yr−1, 73.85 × 104 mol yr−1and 1.19 × 104 mol yr−1, respectively. A much larger flux of methane probably escapes in gaseous form through focused bubble vents. The approach of linking geochemical model results with spatial geophysical data put forward here can be applied elsewhere to improve benthic methane turnover rates from limited single spot measurements to larger spatial scales.

Document Type: Article
Additional Information: Porewater geochemical data used in this study can be obtained upon request via email of mluo@shou.edu.cn.
Keywords: Cold seep; Methane cycling; Reaction-transport modeling; Geophysics; Hikurangi Margin
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems > DeepSea Monitoring
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1002/2016GC006643
ISSN: 1525-2027
Projects: NewVents, NEMESYS
Contribution Number:
ProjectNumber
DSM15
Expeditions/Models/Experiments:
Date Deposited: 11 Nov 2016 07:23
Last Modified: 01 Feb 2019 15:11
URI: http://oceanrep.geomar.de/id/eprint/34636

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