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  • 1
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    Impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern Hikurangi margin (2020)
    Elsevier
    In:  EPIC3Earth andPlanetaryScienceLetters, Elsevier, 541
    Details
    Publication Date: 2020-05-01
    Description: We present geochemical data collected from volcanic ash-bearing sediments on the upper slope of the northern Hikurangi margin during the RV SONNE SO247 expedition in 2016. Gravity coring and seafloor drilling with the MARUM-MeBo200 allowed for collection of sediments down to 105 meters below seafloor (mbsf). Release of dissolved Sr2+with isotopic composition enriched in 86Sr (87Sr/86Sr minimum = 0.708461 at 83.5 mbsf) is indicative of ash alteration. This reaction releases other cations in the 30-70 mbsf depth interval as reflected by maxima in pore-water Ca2+and Ba2+concentrations. In addition, we posit that Fe(III) in volcanogenic glass serves as an electron acceptor for methane oxidation, a reaction that releases Fe2+measured in the pore fluids to a maximum concentration of 184 μM. Several lines of evidence support our proposed coupling of ash alteration with Fe-mediated anaerobic oxidation of methane (Fe-AOM) beneath the sulfate-methane transition (SMT), which lies at ∼7 mbsf at this site. In the ∼30-70 mbsf interval, we observe a concurrent increase in Fe2+and a depletion of CH4with a well-defined decrease in δ13C-CH4values indicative of microbial fractionation of carbon. The negative excursions in δ13C values of both DIC and CH4are similar to that observed by sulfate-driven AOM at low SO2−4concentrations, and can only be explained by the microbially-mediated carbon isotope equilibration between CH4and DIC. Mass balance considerations reveal that the iron cycled through the coupled ash alteration and AOM reactions is consumed as authigenic Fe-bearing minerals. This iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals, as estimated from sequential extraction analyses. Using a numerical modeling approach we estimate the rate of Fe-AOM to be on the order of 0.4μmol cm−2yr−1, which accounts for ∼12% of total CH4removal in the sediments. Although not without uncertainties, the results presented reveal that Fe-AOM in ash-bearing sediments is significantly lower than the sulfate-driven CH4consumption, which at this site is 3.0μmol cm−2yr−1. We highlight that Fe(III) in ash can potentially serve as an electron acceptor for methane oxidation in sulfate-depleted settings. This is relevant to our understanding of C-Fe cycling in the methanic zone that typically underlies the SMT and could be important in supporting the deep biosphere.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 2
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    Anomalous porosity preservation and preferential accumulation of gas hydrate in the Andaman accretionary wedge, NGHP-01 site 17A (2015)
    Elsevier
    Details
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 58A (2014): 99-116, doi:10.1016/j.marpetgeo.2014.04.009.
    Description: In addition to well established properties that control the presence or absence of the hydrate stability zone, such as pressure, temperature, and salinity, additional parameters appear to influence the concentration of gas hydrate in host sediments. The stratigraphic record at Site 17A in the Andaman Sea, eastern Indian Ocean, illustrates the need to better understand the role pore-scale phenomena play in the distribution and presence of marine gas hydrates in a variety of subsurface settings. In this paper we integrate field-generated datasets with newly acquired sedimentology, physical property, imaging and geochemical data with mineral saturation and ion activity products of key mineral phases such as amorphous silica and calcite, to document the presence and nature of secondary precipitates that contributed to anomalous porosity preservation at Site 17A in the Andaman Sea. This study demonstrates the importance of grain-scale subsurface heterogeneities in controlling the occurrence and distribution of concentrated gas hydrate accumulations in marine sediments, and document the importance that increased permeability and enhanced porosity play in supporting gas concentrations sufficient to support gas hydrate formation. The grain scale relationships between porosity, permeability, and gas hydrate saturation documented at Site 17A likely offer insights into what may control the occurrence and distribution of gas hydrate in other sedimentary settings.
    Description: The financial support for the NGHP01, from the Oil Industry Development Board, Oil and Natural Gas Corporation Ltd., GAIL (India) Ltd. and Oil India Ltd. is gratefully acknowledged. We also acknowledge the support extended by all the participating organizations of the NGHP: MoP&NG, DGH, ONGC, GAIL, OIL, NIO, NIOT, and RIL.
    Keywords: Porosity ; Permeability ; Grain size ; Indian Ocean ; Gas hydrate ; Saturation ; Volcanic ash ; Carbonate
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 3
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    Pore fluid chemistry from the Second Gas Hydrate Drilling Expedition in the Ulleung Basin (UBGH2): Source, mechanisms and consequences of fluid freshening in the central part of the Ulleung Basin, East Sea (2013)
    Elsevier
    In:  Marine and Petroleum Geology, 47 . pp. 99-112.
    Details
    Publication Date: 2015-11-04
    Description: During the Second Gas Hydrate Drilling Expedition in the Ulleung Basin (UBGH2), pore fluids were collected from sites that sampled sediments from the continental slope to the basin center, and included locations within and outside seismic identified chimney like features. At five non-chimney sites established during the UBGH2, discrete excursions to low Cl− concentrations within the gas hydrate occurrence zone (GHOZ) are associated with water enriched in δD and δ18O, as expected from gas hydrate dissociation during core recovery. Estimates of gas hydrate saturation values (Sh) based on Cl− and δD values are in good agreement, and show that when gas hydrate occurs in discrete horizons or within strata-bound fractures throughout the GHOZ, it occupies 5–65% of the pore space. Fluids recovered from three sites characterized by seismic inferred chimneys show massive hydrate accumulation near the seafloor, accompanied by the formation of shallow Cl− rich brines with δD and δ18O values lower than seawater. Chemical and isotopic data from fluids sampled at all drilled sites reveal significant fluid freshening below the gas hydrate stability zone (GHSZ). The distribution of Cl−, K+ and δD indicate that the observed freshening is predominantly caused by clay mineral dehydration (illitization). Previously reported heat flow values in the center of the basin indicate that the sediments deeper than 800 mbsf (meter below seafloor) are warm enough to expect clay diagenesis with the onset of smectite-to-illite transformation. Source fluid temperatures 〉70 °C are confirmed through the use of Na+–Li+ and Mg2+–Li+ geothermometry. Based on these observations we propose the following scenario for the evolution of formation fluids in the Ulleung Basin where high formation temperatures and rapid sedimentation at the basin center, led to sediment compaction and clay dehydration reactions that result in fluid overpressures and associated fracturing of the formation. Sediment fractures and fluid (possible gas) migration in the chimney features, imaged in seismic records, are consistent with our postulated upward transport of fluids from 〉800 m depth though the GHSZ and to the seafloor.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marpetgeo.2012.12.011
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern Hikurangi margin (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights • Release of dissolved Sr2+ with low 87Sr/86Sr, as well as Ca2+ and Ba2+ suggests ongoing volcanic ash alteration. • A concurrent increase in Fe2+ and a depletion of CH4 with a decrease in C of CH4 and DIC suggest Fe-AOM. • We for the first time document the potential linkage between ash alteration and methane oxidation via Fe-AOM. • The rate of Fe-AOM is estimated to be ∼0.4 μmol cm−2 yr−1, equivalent to ∼12% of total CH4 removal. Abstract We present geochemical data collected from volcanic ash-bearing sediments on the upper slope of the northern Hikurangi margin during the RV SONNE SO247 expedition in 2016. Gravity coring and seafloor drilling with the MARUM-MeBo200 allowed for collection of sediments down to 105 meters below seafloor (mbsf). Release of dissolved Sr2+ with isotopic composition enriched in 86Sr (87Sr/86Sr minimum = 0.708461 at 83.5 mbsf) is indicative of ash alteration. This reaction releases other cations in the 30-70 mbsf depth interval as reflected by maxima in pore-water Ca2+ and Ba2+ concentrations. In addition, we posit that Fe(III) in volcanogenic glass serves as an electron acceptor for methane oxidation, a reaction that releases Fe2+ measured in the pore fluids to a maximum concentration of 184 μM. Several lines of evidence support our proposed coupling of ash alteration with Fe-mediated anaerobic oxidation of methane (Fe-AOM) beneath the sulfate-methane transition (SMT), which lies at ∼7 mbsf at this site. In the ∼30-70 mbsf interval, we observe a concurrent increase in Fe2+ and a depletion of CH4 with a well-defined decrease in C-CH4 values indicative of microbial fractionation of carbon. The negative excursions in C values of both DIC and CH4 are similar to that observed by sulfate-driven AOM at low SO concentrations, and can only be explained by the microbially-mediated carbon isotope equilibration between CH4 and DIC. Mass balance considerations reveal that the iron cycled through the coupled ash alteration and AOM reactions is consumed as authigenic Fe-bearing minerals. This iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals, as estimated from sequential extraction analyses. Using a numerical modeling approach we estimate the rate of Fe-AOM to be on the order of 0.4 μmol cm−2 yr−1, which accounts for ∼12% of total CH4 removal in the sediments. Although not without uncertainties, the results presented reveal that Fe-AOM in ash-bearing sediments is significantly lower than the sulfate-driven CH4 consumption, which at this site is 3.0 μmol cm−2 yr−1. We highlight that Fe(III) in ash can potentially serve as an electron acceptor for methane oxidation in sulfate-depleted settings. This is relevant to our understanding of C-Fe cycling in the methanic zone that typically underlies the SMT and could be important in supporting the deep biosphere.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Silicate weathering in anoxic marine sediment as a requirement for authigenic carbonate burial (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: We emphasize the importance of marine silicate weathering (MSiW) reactions in anoxic sediment as fundamental in generating alkalinity and cations needed for carbonate precipitation and preservation along continental margins. We use a model that couples thermodynamics with aqueous geochemistry to show that the CO2 released during methanogenesis results in a drop in pH to 6.0; unless these protons are buffered by MSiW, carbonate minerals will dissolve. We present data from two regions: the India passive margin and the active subduction zone off Japan, where ash and/or rivers supply the reactive silicate phase, as reflected in strontium isotope data. Offshore India and Korea, alteration of continent-derived silicates results in pore water enriched in radiogenic 87Sr, with 87Sr/86Sr ratios as high as 0.7095 and 0.7104, respectively. Off Japan, strontium in pore water influenced by ash alteration is depleted in 87Sr, with 87Sr/86Sr as low as 0.7065. Carbonate minerals formed by alkalinity and cations generated through MSiW carry these strontium isotopic signals, and are typically dolomite, siderite, and Fe-rich calcite. These contrast with the aragonite and high-magnesium calcite that form during anaerobic oxidation of methane and incorporate the coeval seawater 87Sr/86Sr signal. We show that MSiW is necessary for authigenic carbonate formation and preservation along continental margins, which remove carbon from Earth's surface at rates previously estimated to be at least 1012 mol yr−1. In addition, these authigenic carbonates are of relevance to studies of the deep biosphere, fluid flow, seismogenesis, slope stability, and reservoir characteristics.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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