Quantitative analytical method for methane hydrates in marine sediments

2003年开展了由北美理工学院(日本)、全俄罗斯海洋地质和矿产研究所(俄罗斯)、V.I.Il‘ichev太平洋海洋学研究所(俄罗斯)、湖泊研究所SB Ras(俄罗斯)、基尔大学莱布尼茨海洋科学研究所(德国)、根特大学(比利时)勒纳德海洋地质中心和韩国极地研究所(韩国)组织的CHOS(鄂霍次克海碳氢水合物积累)合作项目，目的是在鄂霍次克海进行天然气水合物研究。核心采样区位于库页岛近海。在鄂霍次克海830~960m水深范围内，利用重力和水合物探测仪从鄂霍次克海海底提取了含天然气水合物和不含天然气水合物的海洋沉积物，并用KIT公司设计和建造的压榨机采集了孔隙水样。用离子色谱法(硫酸盐和氯化物)、电感耦合等离子体原子发射光谱分析(钠和镁)和火焰原子吸收光谱分析(钾和钙)对孔隙水中硫酸盐、钠等离子进行了测定，发现含天然气水合物沉积物的硫酸盐浓度随深度迅速下降，约为1 mm，约为0.4mbsf，而不含天然气水合物的沉积物，硫酸盐浓度约为3mbsf。由于硫酸盐浓度由于与上升流甲烷的化学反应而降低，海底以下的硫酸盐含量剖面可以提供有关上升流甲烷通量和甲烷水合物形成活动的信息。

The CHAOS (hydro-Carbon Hydrate Accumulations in the Okhotsk Sea) cooperative project organized by Kitami Institute of Technology (KIT, Japan), All Russia Research Institute for Geology and Mineral Resources of the Ocean (Russia), V.I.Il'ichev Pacific Oceanological Institute FEB RAS (Russia), Limnological Institute SB RAS (Russia), Leibniz Institute of Marine Sciences at Kiel University (Germany), Renard center of Marine Geology, Ghent University (Belgium) and Korea Polar Research Institute (Korea)with the aim of the natural gas hydrate study at the Okhotsk Sea was conducted in 2003. The core sampling areas were located offshore Sakhalin Island. The gas hydrate-bearing and gas hydrate-free marine sediments were retrieved from the bottom of the Okhotsk Sea at water depths between 830 and 960 m by using gravity and hydro-corers.The pore water samples were obtained by a squeezer designed and constructed at KIT. Determination of ions such as sulfate, sodium etc. in the pore water was carried out by ion chromatography (sulfate and chloride), inductively coupled plasma atomic emission spectrometry (sodium and magnesium) and flame atomic absorption spectrometry (potassium and calcium).It was found that the sulfate concentration decreased rapidly with depth to ca. 1 mM at about 0.4 mbsf for the gas hydrate-bearing sediments whereas the depth was about 3 mbsf for the sediments without gas hydrate. Since sulfate concentration decreases due to chemical reactions with upwelling methane, sulfate content profile below sea floor can provide information about upwelling methane flux and methane hydrates formation activity.