Study of methane metabolic cycle of microorganisms in marine sediment core using natural level radiocarbon analysis

本研究旨在开发各种评估技术，以澄清海洋沉积物中与甲烷水合物有关的生物标志物信号及其信号强度，无论这些信号是沉积物中活微生物新产生的，还是现场的甲烷源碳。首先，开发了一种石墨化技术，可以对碳含量低于100 μg的小样品进行精确的放射性碳测量。微尺度放射性碳分析技术的发展对有机地球化学等各个研究领域的深入研究具有重要意义。利用该方法，对近年来发现含有大量甲烷水合物的洋潮陆坡沉积物柱状岩心进行了34 kyr浮游生物和底栖有孔虫碳同位素记录的研究。此外，为了研究有孔虫碳同位素信号与海底甲烷释放的关系，结合上覆水柱和表层沉积物中氧化-缺氧界面中甲烷营养细菌的历史活动，分析了生物标志物组成及其碳同位素。为了分析海洋沉积物岩心中微生物群落和微生物RNA，我们改进并开发了以木苏湾沉积物为研究对象的DNA/RNA同时提取方法。在沉积物岩心中鉴定出与产甲烷菌和养甲烷菌相关的部分16S rDNA序列。

This research was executed to develop various evaluation techniques for clarifying biomarker signals and their signal strength left for marine sediments concerning about methane hydrate, whether these signal had been newly generated by living microorganisms in the sediment or they were methane origin carbon on the site. At first, a graphitization technique for making precise and accurate radiocarbon measurements on small samples containing less than 100 μg of carbon was developed. The development of a microscale radiocarbon analysis technique is very important for advanced research in various fields of study, especially organic geochemistry. Using this method, the piston cores from the continental slope sediments in the Oyashio current region, which recently is found to bear immense amounts of methane hydrate, have been investigated about planktonic and benthic foraminiferal carbon isotope records during the past 34 kyr. Moreover, in order to investigate relation with foraminifera carbon isotopic signal and methane release from the seafloor, biomarker compositions and their carbon isotope have been analyzed in the light of the past activity of methanotrophic bacteria in the oxic-anoxic interface in the overlying water column and/or surface sediment. To analysis for microbial communities and microbial RNA in marine sediment core, we modified and developed DNA/RNA simultaneous extraction method using the Mutsu-bay sediments. We identified several partial sequences of 16S rDNA related to methanogens and methanotrophs in the sediment cores.