南海东沙海域晚更新世以来天然气水合物分解/释放规模的分子有机地球化学记录及环境效应

High attention and wide acceptance has paid to gas hydrate for it is taken as one of the most important energy sources in the 21st century．Yet it is more important and significant to full understand the gas hydrates dissociation and its relationship with the climatic and environmental change in geological time for the exploration and exploitation of gas hydrate. Promising gas hydrate deposits were confirmed in Dongsha Area, the South China Sea (SCS) during the latest integrated investigation. However, little is known about the sedimentary records of gas hydrates dissociation in geological time, especially the anaerobic oxidation of methane (AOM) processes and their lipid biomarkers. .This research is focused on the compositions of molecular biomarkers related to AOM and the paleoenvironmental reconstruction in Dongsha Area, the South China Sea since Late Pleistocene. Several aspects will be involved, including: (1) the quantitative and qualitative research of AOM-related biomarkers in the core sediment will performed, which could provide the information on the time and/or depth that gas hydrates dissociated in the past. (2) The composition and distribution of glycerol dialkyl glycerol tetraethers (GDGTs) in the core sediment will be investigated, which could provide the information on the biological sources of GDGTs. GDGT-based methane index will be calculated and the relative scale of gas hydrates dissociation would be evaluated. (3) The long-chain ketones will be studied and the UK’ 37‒SST will be reconstructed for the same core sediment. All these achievements would enable us to judge and evaluate the relationship between the gas hydrates dissociation and the paleoenvironmental change in the SCS since Late Pleistocene.

天然气水合物作为21世纪重要能源已受到广泛认可和高度关注，详细了解地质历史时期海洋水合物分解/释放的沉积记录及其与气候环境变化的关系，对于海洋水合物资源的勘探和开采有着重要的理论实际意义。我国南海东沙海域是天然气水合物有利远景区，但关于地质历史时期天然气水合物分解的沉积记录系统研究还非常缺乏。本项目将通过分子有机地球化学手段，对东沙海域柱状沉积物进行高分辨率分子标志化合物研究。重点①对与甲烷厌氧氧化(AOM)相关的特征生物标志化合物进行定性、定量研究，以判断晚更新世以来本海域发生水合物分解的具体层位 (或时间)。②对沉积记录的GDGTs 进行定性、定量研究，分析其组成和源输入特征，计算甲烷指数 (MI)，以判断水合物分解的相对规模。③长链烯酮分析，通过UK’ 37指标重建晚更新世以来本海域的表层水体温度，在此基础之上探讨该地区晚更新世以来气候/环境演化与天然气水合物分解/释放之间的关系。

天然气水合物作为21世纪的重要能源已受到广泛认可和高度关注，详细了解地质历史时期海洋水合物分解/释放的沉积记录及其与气候环境变化的关系，对于海洋水合物资源的勘探和开采有着重要的理论实际意义。我国南海东沙海域是天然气水合物有利远景区，但关于地质历史时期天然气水合物分解的沉积记录系统研究还非常缺乏。本项研究通过对在东沙海区获取的3根柱状沉积物进行高分辨率分子标志化合物的定性和定量研究, 计算了甲烷指数 (MI), 获得了该海区自50.0 kaBP以来水合物分解/释放的具体层位和相对规模的记录; 利用有机地球化学指标重建了50.0 kaBP以来该海区的表层水体温度的变化历史。结果发现,地质历史时期东沙海区小范围的水合物分解/释放并没有导致整个海区的表层水体温度明显升高, 该海区50.0 kaBP以来表层水体温度的变化还主要受控于冰期/间冰期旋回等气候事件。