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
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
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贝加尔湖库库伊泥火山连续采样的天然气水合物水，加上孔隙水和底层水同位素和离子特征：水合物形成水的不明确的深层来源
DOI：
10.1007/s00367-014-0364-4
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发表时间：
2014
影响因子：
2.1
通讯作者：
Marc De Batist
中科院分区：
文献类型：
--
作者：
Minami;Hirotsugu;Akihiro Hachikubo;Hirotoshi Sakagami;Satoshi Yamashita;Yusuke Soramoto;Tsuyoshi Kotake;Nobuo Takahashi;Hitoshi Shoji;Tatyana Pogodaeva;Oleg Khlystov;Andrey Khabuev;Lieven Naudts;Marc De Batist
研究了贝加尔湖Kukuy K-9泥火山（MV）三个重力岩心（165-193 cm长）中天然气水合物（GH）的同位素和离子组成。在封闭的玻璃室中，在6小时内逐步解离来自St 6 GC 4岩心（143-165 cm岩心深度间隔）的大量GH样品，并分析了11个连续收集的解离GH水馏分。它们的氢和氧同位素组成，以及Cl-和HCO 3-的浓度基本上保持不变，随着时间的推移，除了在第一个50分钟收集的馏分部分偏离这一模式。馏分#1具有显著更高的Cl-浓度，类似于在该岩心中的主要含GH层段上方（135-142 cm岩心深度）取样的孔隙水。然而，像随后的馏分，HCO 3-浓度显着低于孔隙水。对于GH水馏分#2至#11，基本恒定的HCO 3-/Cl-比305与井下孔隙水HCO 3-/Cl-比63-99显著不同。显然，环境孔隙水可能粘附在大量GH样品上的提取GH水的污染令人满意地限制在GH解离的初始阶段。水合物形成水的氢和氧同位素组成估计使用提取GH水的同位素组成结合已知的GH和GH形成水之间的同位素分馏因子。在St 6 GC 4取芯点，δD值为−126 ‰至−133‰，δ 18 O值为−15.7 ‰至−16.7‰，这与周围孔隙水（δD值为−123‰，δ 18 O值为−15.6‰）和湖底水（δD值为−121‰，δ 18 O值为−15.8‰）的相应特征部分不同，表明GH不是由这些沃茨形成的。该核心中角砾岩的观测结果表明可能存在深层水源，与邻近Kukuy K-2 MV的已发表热测量结果一致。相比之下，Kukuy K-9 MV的St 6 GC 4岩心以及相邻岩心GC 2和GC 3的孔隙沃茨既没有显示出这种来源的同位素证据，也没有显示出这种来源的离子证据（例如，硫酸盐浓度升高）。这些发现限制生长激素的形成，以更早的时间，但根深蒂固的水合物形成水的来源仍然是模糊的。关键的深水源特征可能长期受到抑制，值得进一步关注，特别是在扩散和（或）平流以及甲烷厌氧氧化方面。
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 δD of −126 to −133‰ and δ18O of −15.7 to −16.7‰ differed partly from the corresponding signatures of ambient pore water (δD of −123‰, δ18O of −15.6‰) and of lake bottom water (δD of −121‰, δ18O of −15.8‰) 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.