Silicate weathering in anoxic marine sediment as a requirement for authigenic carbonate burial

Marta E. Torres, Wei Li Hong, Evan A. Solomon, Kitty Milliken, Ji Hoon Kim, James C. Sample, Barbara M.A. Teichert, Klaus Wallmann

Research output: Contribution to journalReview article

Abstract

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.

Original languageEnglish (US)
Article number102960
JournalEarth-Science Reviews
Volume200
DOIs
StatePublished - Jan 2020

Fingerprint

anoxic sediment
marine sediment
weathering
silicate
carbonate
strontium
alkalinity
continental margin
porewater
ash
calcite
cation
strontium isotope
siderite
methanogenesis
passive margin
mineral
aragonite
slope stability
biosphere

Keywords

  • Alkalinity
  • Authigenic carbonate
  • Carbon cycling
  • Organogenic dolomite
  • Silicate weathering

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

Cite this

Silicate weathering in anoxic marine sediment as a requirement for authigenic carbonate burial. / Torres, Marta E.; Hong, Wei Li; Solomon, Evan A.; Milliken, Kitty; Kim, Ji Hoon; Sample, James C.; Teichert, Barbara M.A.; Wallmann, Klaus.

In: Earth-Science Reviews, Vol. 200, 102960, 01.2020.

Research output: Contribution to journalReview article

Torres, Marta E. ; Hong, Wei Li ; Solomon, Evan A. ; Milliken, Kitty ; Kim, Ji Hoon ; Sample, James C. ; Teichert, Barbara M.A. ; Wallmann, Klaus. / Silicate weathering in anoxic marine sediment as a requirement for authigenic carbonate burial. In: Earth-Science Reviews. 2020 ; Vol. 200.
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abstract = "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.",
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