|Alternative Title||Geochemical Characteristics of the Sediments and Bottom Seawater near Hydrothermal fields , Mid-Okinawa Trough|
|Place of Conferral||北京|
|Keyword||冲绳海槽中部 原位气体测量 热液喷口 沉积物|
|Abstract||本文通过搭载于无人遥控潜水器ROV上的多种原位实测传感器（甲烷传感器、二氧化碳传感器及CTD等），对冲绳海槽中部热液活动区Iheya North和CLAM区近海底水体相关特征进行了研究，首次分析了不同活跃程度的热液区喷口附近海水水体中溶解甲烷和二氧化碳的水体特征。同时，结合ROV上拍摄的视频资料和研究区水体温度分布特征，初步讨论了温度对热液区生物聚集的影响。此外，通过搭载于ROV上的浅表层Push Core取样器首次获取距离热液喷口仅35 m的热液区沉积物样品。通过分析得出近喷口热液沉积物独特的的地球化学特征。|
Iheya North热液区远离热液口（正常海水）的近海底水体中甲烷和二氧化碳气体浓度为0μmol/l和400 ppm。黑烟囱喷口附近甲烷和二氧化碳浓度达到最高值，分别为8μmol/l和12000 ppm。不过，在低温溢流区附近甲烷和二氧化碳浓度相比黑烟囱喷口区减小，保持在2μmol/l和4000 ppm左右。尽管如此，低温溢流区二氧化碳浓度亦是正常海水中二氧化碳浓度的10倍之多。CLAM热液区没有正在喷发的黑烟囱，仅在热液生物曾经大量聚集区检测到最高浓度为2200ppm的二氧化碳。该区二氧化碳浓度仅仅是Iheya North区二氧化碳浓度的六分之一。由于前人主要通过对热液流体性质展开相关研究，发现冲绳海槽热液区气体的富集特点。本文首次通过海底原位气体传感器对热液区周围海水水体中溶解气体浓度的检测验证了冲绳海槽热液喷口喷发大量甲烷和二氧化碳气体，并且高出传统气相色谱法检测浓度至少四个数量级。
浅表层沉积物相关的地球化学特征表明，本次研究样品主要组分主要为SO3, ZnO 和 Fe2O3，与正常海底沉积物中以Al2O3, SiO2 和 CaO为主要成分的沉积物明显不同。此外，元素的相关分析表明锶、汞和银可以作为热液特征组分。一些微量元素如Cu, Pb, Zn, As, Sb, Hg, Se, Ag, Ba, Mo 和 Cd在近喷口热液沉积物中也高度富集。元素的因子分析进一步反映热液沉积物来源主要是热液源。锶同位素比值进一步表明Iheya North热液区具有较弱的沉积物/流体相互作用。
|Other Abstract||With the application of the in situ sensors (carbon dioxide sensors, methane sensors and CTD) carried by ROV (Remotely Operated Vehicle), properties of bottom seawater were revealed in Iheya North and CLAM hydrothermal fields in mid-Okinawa Trough. Besides, it is also the first time to have a comprehensive analysis of methane and carbon dioxide dissolved in seawater near different activity hydrothermal fields. At the meanwhile, the control factors of hydrothermal faunas assemblage were priliminary discussed combined with video materials and distribution characteristics of seawater temperatures. On the other hand, the surface hydrothermal sediments were first collected by push core mounted on ROV, and the distance between hydrothermal vent and sampled site were only about 35 m. However, previous sampled sediments collected by grab had a long distance to hydrothemral vent. Therefore, unique geochemical characteristics of near hydrothermal vents were indicated through analysis.|
The results of methane and carbon dioxide concentration dissolved in seawater far from hydrothermal vent ( normal seawater) were 0 μmol/l and 400 ppm, respectively. However, the counterparts near black smoker reach up to 8μmol/l and 12000 ppm, which are relative higher than those near low-temperature diffusive oriface, with the concentrations of 2 μmol/l and 4000 ppm. In spite of this, it is still ten times higher than normal seawater in terms of concentrations of carbon dioxide. The other studied hydrothermal field- CLAM, was featured by dead chimneys, and there was no vigourously venting black smoker observed during this research. There was no methane detected, and only carbon dioxide was found near dying hydrothermal fauna assemblage, the maximum concentraion was 2200 ppm. As previous scholars focused more on hydrothermal fluids, and proved the enrichment of carbon dioxide and methane in hydrothermal fluids. However, little attention was paid on seawater near hydrothermal vents. In this research, carbon dioxide and methane gas dissolved in seawater were first detected by in situ sensors, and has at least four magnitude greater than traditional gas chromatograph due to the vicinity to sampled seawater.
The geochemical characteristics of surface hydrothermal sediments indicated that major components are SO3, ZnO and Fe2O3, which shows an obvious distinction to normal seafloor sediments. The latter is characterized by Al2O3, SiO2 and CaO. In addition, the related analysis reflects Sr, Hg and Ag are the hydrothermal indicators. Some minor elements like Cu, Pb, Zn, As, Sb, Hg, Se, Ag, Ba, Mo and Cd are also highly enriched in hydrothermal sediments. What is more, the R-mode factor analysis further shows the collected sediments are mainly from hydrothermal input, terrestrial input and biogenous input. It is also suggested weak interactions between sediments/hydrothermal fluids by strontium ratios.
|胡倩男. 冲绳海槽中部热液区近海底水体及沉积物地球化学特征[D]. 北京. 中国科学院大学,2016.|
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