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Sequentially sampled gas hydrate water, coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano, Lake Baikal: ambiguous deep-rooted source of hydrate-forming water

(2014) GEO-MARINE LETTERS. 34(2-3). p.241-251
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Abstract
The isotopic and ionic composition of pure gas hydrate (GH) water was examined for GHs recovered in three gravity cores (165-193 cm length) from the Kukuy K-9 mud volcano (MV) in Lake Baikal. A massive GH sample from core St6GC4 (143-165 cm core depth interval) was dissociated progressively over 6 h in a closed glass chamber, and 11 sequentially collected fractions of dissociated GH water analyzed. Their hydrogen and oxygen isotopic compositions, and the concentrations of Cl- and HCO3 (-) remained essentially constant over time, except that the fraction collected during the first 50 minutes deviated partly from this pattern. Fraction #1 had a substantially higher Cl- concentration, similar to that of pore water sampled immediately above (135-142 cm core depth) the main GH-bearing interval in that core. Like the subsequent fractions, however, the HCO3 (-) concentration was markedly lower than that of pore water. For the GH water fractions #2 to #11, an essentially constant HCO3 (-)/Cl- ratio of 305 differed markedly from downcore pore water HCO3 (-)/Cl- ratios of 63-99. Evidently, contamination of the extracted GH water by ambient pore water probably adhered to the massive GH sample was satisfactorily restricted to the initial phase of GH dissociation. The hydrogen and oxygen isotopic composition of hydrate-forming water was estimated using the measured isotopic composition of extracted GH water combined with known isotopic fractionation factors between GH and GH-forming water. Estimated delta D of -126 to -133aEuro degrees and delta O-18 of -15.7 to -16.7aEuro degrees differed partly from the corresponding signatures of ambient pore water (delta D of -123aEuro degrees, delta O-18 of -15.6aEuro degrees) and of lake bottom water (delta D of -121aEuro degrees, delta O-18 of -15.8aEuro degrees) at the St6GC4 coring site, suggesting that the GH was not formed from those waters. Observations of breccias in that core point to a possible deep-rooted water source, consistent with published thermal measurements for the neighboring Kukuy K-2 MV. By contrast, the pore waters of core St6GC4 and also of the neighboring cores GC2 and GC3 from the Kukuy K-9 MV show neither isotopic nor ionic evidence of such a source (e.g., elevated sulfate concentration). These findings constrain GH formation to earlier times, but a deep-rooted source of hydrate-forming water remains ambiguous. A possible long-term dampening of key deep-water source signatures deserves further attention, notably in terms of diffusion and/or advection, as well as anaerobic oxidation of methane.
Keywords
METHANE PLUMES, ANAEROBIC OXIDATION, BLAKE RIDGE, SEDIMENTS, ANOMALIES, SIBERIA, DESTABILIZATION, FRACTIONATION, DISSOCIATION, SUBSURFACE

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Chicago
Minami, Hirotsugu, Akihiro Hachikubo, Hirotoshi Sakagami, Satoshi Yamashita, Yusuke Soramoto, Tsuyoshi Kotake, Nobuo Takahashi, et al. 2014. “Sequentially Sampled Gas Hydrate Water, Coupled with Pore Water and Bottom Water Isotopic and Ionic Signatures at the Kukuy Mud Volcano, Lake Baikal: Ambiguous Deep-rooted Source of Hydrate-forming Water.” Geo-marine Letters 34 (2-3): 241–251.
APA
Minami, H., Hachikubo, A., Sakagami, H., Yamashita, S., Soramoto, Y., Kotake, T., Takahashi, N., et al. (2014). Sequentially sampled gas hydrate water, coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano, Lake Baikal: ambiguous deep-rooted source of hydrate-forming water. GEO-MARINE LETTERS, 34(2-3), 241–251.
Vancouver
1.
Minami H, Hachikubo A, Sakagami H, Yamashita S, Soramoto Y, Kotake T, et al. Sequentially sampled gas hydrate water, coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano, Lake Baikal: ambiguous deep-rooted source of hydrate-forming water. GEO-MARINE LETTERS. 2014;34(2-3):241–51.
MLA
Minami, Hirotsugu, Akihiro Hachikubo, Hirotoshi Sakagami, et al. “Sequentially Sampled Gas Hydrate Water, Coupled with Pore Water and Bottom Water Isotopic and Ionic Signatures at the Kukuy Mud Volcano, Lake Baikal: Ambiguous Deep-rooted Source of Hydrate-forming Water.” GEO-MARINE LETTERS 34.2-3 (2014): 241–251. Print.
@article{5664822,
  abstract     = {The isotopic and ionic composition of pure gas hydrate (GH) water was examined for GHs recovered in three gravity cores (165-193 cm length) from the Kukuy K-9 mud volcano (MV) in Lake Baikal. A massive GH sample from core St6GC4 (143-165 cm core depth interval) was dissociated progressively over 6 h in a closed glass chamber, and 11 sequentially collected fractions of dissociated GH water analyzed. Their hydrogen and oxygen isotopic compositions, and the concentrations of Cl- and HCO3 (-) remained essentially constant over time, except that the fraction collected during the first 50 minutes deviated partly from this pattern. Fraction #1 had a substantially higher Cl- concentration, similar to that of pore water sampled immediately above (135-142 cm core depth) the main GH-bearing interval in that core. Like the subsequent fractions, however, the HCO3 (-) concentration was markedly lower than that of pore water. For the GH water fractions #2 to #11, an essentially constant HCO3 (-)/Cl- ratio of 305 differed markedly from downcore pore water HCO3 (-)/Cl- ratios of 63-99. Evidently, contamination of the extracted GH water by ambient pore water probably adhered to the massive GH sample was satisfactorily restricted to the initial phase of GH dissociation. The hydrogen and oxygen isotopic composition of hydrate-forming water was estimated using the measured isotopic composition of extracted GH water combined with known isotopic fractionation factors between GH and GH-forming water. Estimated delta D of -126 to -133aEuro degrees and delta O-18 of -15.7 to -16.7aEuro degrees differed partly from the corresponding signatures of ambient pore water (delta D of -123aEuro degrees, delta O-18 of -15.6aEuro degrees) and of lake bottom water (delta D of -121aEuro degrees, delta O-18 of -15.8aEuro degrees) at the St6GC4 coring site, suggesting that the GH was not formed from those waters. Observations of breccias in that core point to a possible deep-rooted water source, consistent with published thermal measurements for the neighboring Kukuy K-2 MV. By contrast, the pore waters of core St6GC4 and also of the neighboring cores GC2 and GC3 from the Kukuy K-9 MV show neither isotopic nor ionic evidence of such a source (e.g., elevated sulfate concentration). These findings constrain GH formation to earlier times, but a deep-rooted source of hydrate-forming water remains ambiguous. A possible long-term dampening of key deep-water source signatures deserves further attention, notably in terms of diffusion and/or advection, as well as anaerobic oxidation of methane.},
  author       = {Minami, Hirotsugu and Hachikubo, Akihiro and Sakagami, Hirotoshi and Yamashita, Satoshi and Soramoto, Yusuke and Kotake, Tsuyoshi and Takahashi, Nobuo and Shoji, Hitoshi and Pogodaeva, Tatyana and Khlystov, Oleg and Khabuev, Andrey and Naudts, Lieven and De Batist, Marc},
  issn         = {0276-0460},
  journal      = {GEO-MARINE LETTERS},
  keywords     = {METHANE PLUMES,ANAEROBIC OXIDATION,BLAKE RIDGE,SEDIMENTS,ANOMALIES,SIBERIA,DESTABILIZATION,FRACTIONATION,DISSOCIATION,SUBSURFACE},
  language     = {eng},
  number       = {2-3},
  pages        = {241--251},
  title        = {Sequentially sampled gas hydrate water, coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano, Lake Baikal: ambiguous deep-rooted source of hydrate-forming water},
  url          = {http://dx.doi.org/10.1007/s00367-014-0364-4},
  volume       = {34},
  year         = {2014},
}

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