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Luo, Min; Torres, Marta; Hong, Wei-Li; Pape, Thomas; Fronzek, Julia; Kutterolf, Steffen; Mountjoy, Joshua; Orpin, Alan R; Henkel, Susann; Huhn, Katrin; Chen, Duofu; Kasten, Sabine (2020): Methane concentrations and stable carbon isotopic composition of methane in headspace gas prepared from sediment cores at the Tuaheni slide complex east of New Zealand's North Island. PANGAEA, https://doi.org/10.1594/PANGAEA.914944

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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.
Keyword(s):
DSRV SONNE; Hikurangi Margin; MeBo200; Methane; New Zealand; SlamZ project; SO247; stable carbon isotopic composition; Tuaheni slide complex
Supplement to:
Luo, Min; Torres, Marta E; Hong, Wei-Li; Pape, Thomas; Fronzek, Julia; Kutterolf, Steffen; Mountjoy, Joshu J; Orpin, Alan R; Henkel, Susann; Huhn, Katrin; Chen, Duofu; Kasten, Sabine (2020): Impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern Hikurangi margin. Earth and Planetary Science Letters, 541, 116288, https://doi.org/10.1016/j.epsl.2020.116288
Further details:
Huhn, Katrin (2016): Cruise Report / Fahrtbericht SO247 - SlamZ: Slide activity on the Hikurangi margin, New Zealand, Wellington (NZ): 27.03.2016 - Auckland (NZ): 27.04.2016. MARUM, Center for Marine Environmental Sciences, University of Bremen, Germany, 119 pp, https://doi.org/10.2312/cr_so247
Coverage:
Median Latitude: -38.765794 * Median Longitude: 178.483060 * South-bound Latitude: -38.766250 * West-bound Longitude: 178.482633 * North-bound Latitude: -38.765500 * East-bound Longitude: 178.483850
Date/Time Start: 2016-03-28T19:28:00 * Date/Time End: 2016-04-18T06:50:00
Size:
8 datasets

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Datasets listed in this publication series

  1. Pape, T; Crutchley, GJ; Torres, ME et al. (2020): Methane concentrations (uncorrected for sediment porosity and Bunsen coefficient) in headspace gas prepared from MeBo core GeoB20802-3 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914932
  2. Pape, T; Crutchley, GJ; Torres, ME et al. (2020): Methane concentrations (uncorrected for sediment porosity and Bunsen coefficient) in headspace gas prepared from MeBo core GeoB20802-4 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914928
  3. Pape, T; Crutchley, GJ; Torres, ME et al. (2020): Methane concentrations (uncorrected for sediment porosity and Bunsen coefficient) in headspace gas prepared from MeBo core GeoB20802-5 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914929
  4. Pape, T; Crutchley, GJ; Torres, ME et al. (2020): Methane concentrations (uncorrected for sediment porosity and Bunsen coefficient) in headspace gas prepared from MeBo core GeoB20802-6 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914931
  5. Pape, T; Crutchley, GJ; Torres, ME et al. (2020): Methane concentrations (uncorrected for sediment porosity and Bunsen coefficient) in headspace gas prepared from gravity core GeoB20802-2 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914930
  6. Pape, T; Malnati, J (2020): Stable carbon isotopic composition of methane (δ13C-CH4) in headspace gas prepared from MeBo core GeoB20802-4 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914939
  7. Pape, T; Malnati, J (2020): Stable carbon isotopic composition of methane (δ13C-CH4) in headspace gas prepared from MeBo core GeoB20802-5 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914940
  8. Pape, T; Malnati, J (2020): Stable carbon isotopic composition of methane (δ13C-CH4) in headspace gas prepared from MeBo core GeoB20802-6 recovered from the Tuaheni slide complex east of New Zealand's North Island. https://doi.org/10.1594/PANGAEA.914941