南海南沙海区沉积有机质分布特征及其指示意义  

Spatial distribution of organic matter in surface sediments from the Nansha sea area of the South China Sea and its implications for marine productivity and monsoon

作　　者：陈芬 黎刚[1,3] 朱小畏 颜文[1,2,3] CHEN Fen;LI Gang;ZHU Xiaowei;YAN Wen(Key Laboratory of Ocean and Marginal Sea Geology,South China Sea Institute of Oceanography,CAS,Guangzhou 510301,China;University of Chinese Academy of Sciences,Beijing 100049,China;South Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China)

机构地区：[1]中国科学院南海海洋研究所边缘海与大洋地质重点实验室,广州510301 [2]中国科学院大学,北京100049 [3]南方海洋科学与工程广东省实验室(广州),广州511458

出　　处：《海洋地质与第四纪地质》2023年第2期45-54,共10页Marine Geology & Quaternary Geology

基　　金：广东省基础与应用基础研究基金“南科1井珊瑚礁体生物标志物及其碳同位素组成分布特征及环境意义”(2022A1515012182);国家自然科学基金面上项目“末次冰期以来南海南部南海中层水的氧化性研究”(42176079),“末次盛冰期以来北阿拉伯海(莫克兰)低氧带的千年尺度变化及其控制机制研究”(41976062);国家自然科学基金项目“南科1井‘混色沉积夹层’的物质组成与微观组构及其成因机制研究”(41976063)。

摘　　要：对现在过程的研究可为了解过去沉积环境演变信息提供重要线索。对南海南沙广阔海域23个现代表层沉积物样品总有机碳(TOC)、总氮(TN)含量及同位素组成(δ13CTOC和δ15N)进行测试分析,以期通过沉积有机质的现代组成分布特征为反演其历史时空分布变化规律及其驱动机制提供参考。南沙海区表层沉积物TOC/TN(5.5~7.9,平均为6.5±0.6)和δ13CTOC(–21.9‰~–18.7‰,平均为–21.0‰±0.7‰)揭示了沉积有机质主要来自海源贡献;δ13CTOC与TOC和TOC/TN的相关性分析表明了TOC未受明显的早期成岩作用影响,因此表层沉积物TOC可用于反映现代上层海水生产力状况。南沙海区表层沉积物TOC(0.32%~0.97%,平均为0.67%±0.17%)呈现明显的西-东向分布差异,高值主要位于西部前缘地带,低值主要分布在东部海域。表层沉积物TOC的地理分布特征表明了西南夏季风对南沙海域表层海水生产力的主要调控作用—由夏季风产生的越南上升流和湄公河陆源输入带来的高通量营养盐促进了西部前缘海域浮游植物的勃发,而随着站位距离的增加其施肥效应越来越弱。表层沉积物TOC和TN的强相关性(R2=0.95)以及δ15N的空间分布特征暗示了南沙海域沉积物δ15N未受陆源河流影响,记录了上层海水δ15N信号,从而指示了相关的氮循环过程。The knowledge of modern hydrologic process provides important clues for marine palaeoenvironmental and palaeoclimatic evolution.Twenty-three surface sediment samples collected throughout the Nansha sea area of the South China Sea(SCS)were analyzed for sedimentary bulk parameters,including total organic carbon(TOC),total nitrogen(TN)and their isotopes(δ13CTOC andδ15N),in order to understand the controlling factors on the spatiotemporal variations of sedimentary organic matter(OM).Results show that the TOC/TN(5.5~7.9 in range and 6.5±0.6 on average)andδ13CTOC(–21.9‰~–18.7‰in range and–21.0‰±0.7‰on average)reflect the dominance of marine OM input to surface sediments in the Nansha sea area.Correlation analyses ofδ13CTOC vs TOC and vs TOC/TN indicate that sedimentary TOC was not significantly affected by early diagenesis,thereby TOC can be used as an effective tracer for surface productivity.The values of TOC(0.32%~0.97%in range and 0.67%±0.17%on average)show a descending trend from the western to eastern parts of the Nansha sea area,indicating clearly the importance of southwesterly summer monsoon in delivering rich nutrients from the productive Vietnam upwelling and Mekong delta.Moreover,strong correlation between TOC and TN(R2=0.95)and clear spatial distribution ofδ15N manifested the ability of bulkδ15N to reflect upper waterδ15N signal due to the minimal influence of riverine terrigenous inorganic N,thereby indicating the relevant nitrogen cycle process.

关 键 词：表层沉积物 有机质来源 海洋生产力 东亚季风 南沙海区 

分 类 号：P736.4[天文地球—海洋地质]