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

Type Article
Date 2019-11
Language English
Author(s) Zindorf Mark1, März Christian1, 2, Wagner Thomas1, 3, Gulick Sean P.S.4, Strauss Harald5, Benowitz Jeff6, Jaeger John7, Schnetger Bernhard8, Childress Laurel9, Levay Leah9, Van Der Land Cees1, La Rosa Michelle8
Affiliation(s) 1 : School of Natural and Environmental Sciences, Newcastle University, NE1 7RU Newcastle upon Tyne, United Kingdom
2 : School of Earth and Environment, University of Leeds, LS2 9JT Leeds, United Kingdom
3 : The Lyell Centre, School of Energy Geoscience Infrastructure and Society, Heriot-Watt University, EH14 4HS Edinburgh, United Kingdom
4 : Institute for Geophysics, Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78758-4445, USA
5 : Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
6 : Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, USA
7 : Department of Geological Sciences, University of Florida, Gainesville, FL 32611-2120, USA
8 : Institut für Chemie und Biologie des Meeres (ICBM), Universität Oldenburg, 26129 Oldenburg, Germany
9 : International Ocean Discovery Program, Texas A&M University, College Station, TX 77845-9547, USA
Source Marine Geology (0025-3227) (Elsevier BV), 2019-11 , Vol. 417 , P. 105986 (15p.)
DOI 10.1016/j.margeo.2019.105986
WOS© Times Cited 4
Keyword(s) Early diagenesis, Sulfate-Methane Transition Zone, Sulfur isotopes, Inverse diagenetic zonation, Gulf of Alaska, IODP

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 sulfate- and 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.

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Zindorf Mark, März Christian, Wagner Thomas, Gulick Sean P.S., Strauss Harald, Benowitz Jeff, Jaeger John, Schnetger Bernhard, Childress Laurel, Levay Leah, Van Der Land Cees, La Rosa Michelle (2019). Deep Sulfate-Methane-Transition and sediment diagenesis in the Gulf of Alaska (IODP Site U1417). Marine Geology, 417, 105986 (15p.). Publisher's official version : , Open Access version :