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Deep Sulfate-Methane-Transition and sediment diagenesis in the Gulf of Alaska (IODP Site U1417)

Lookup NU author(s): Mark Zindorf, Professor Thomas Wagner, Dr Cees van der Land

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This is the authors' accepted manuscript of an article that has been published in its final definitive form by Elsevier, 2019.

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Abstract

Sediment samples from the Gulf of Alaska (GOA, IODP Expedition 341, Site U1417) have been analyzed to understand present and past diagenetic processes that overprint the primary sediment composition. No Sulfate-Methane Transition Zone (SMTZ) was observed at the zone of sulfate depletion, but a > 200 m thick sulfateand methane-free sediment interval occurred between the depth of sulfate depletion (~200 m) and the onset of methanogenesis (~440 m). We suggest that this apparent gap in biogeochemical processing of organic matter is caused by anaerobic oxidation of methane fueled by sulfate which is released during dissolution of barites at the upper boundary of the methane rich layer. Beneath the methanogenic zone, at ~650 m depth, pore-water sulfate concentrations increase again, indicating sulfate supply from greater depth feeding into a deep, inverse SMTZ. A likely explanation for the availability of sulfate in the deep sub-seafloor at U1417 is the existence of a deep aquifer related to plate bending fractures, which actively transports sulfate-rich water to, and potentially along, the interface between sediments and oceanic crust. Such inverse diagenetic zonations have been previously observed in marine sediments, but have not yet been linked to subduction-related plate bending. With the discovery of a deep inverse SMTZ in an intra-oceanic plate setting and the blocking of upward methane diffusion by sulfate released from authigenic barite dissolution, Site U1417 provides new insights into sub-seafloor pore-fluid and gas dynamics, and their implications for global element cycling and the deep biosphere


Publication metadata

Author(s): Zindorf M, März C, Wagner T, Gulick S, Strauss H, Benowitz J, Jaeger JM, Schnetger B, Childress L, LeVay L, Van der Land C, La Rosa M

Publication type: Article

Publication status: Published

Journal: Marine Geology

Year: 2019

Volume: 417

Print publication date: 01/11/2019

Online publication date: 22/07/2019

Acceptance date: 08/07/2019

Date deposited: 05/08/2019

ISSN (print): 0025-3227

ISSN (electronic): 1872-6151

Publisher: Elsevier

URL: https://doi.org/10.1016/j.margeo.2019.105986

DOI: 10.1016/j.margeo.2019.105986


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