南海神狐海域水合物发育区浅表层沉积物甲烷周转定量模拟  

Quantitative assessment of methane turnover in shallow surface sediments of hydrate-bearing areas in Shenhu area of South China Sea

作　　者：胡廷苍 张艳平 胡钰[1] 罗敏[1] 陈多福[1] HU Tingcang;ZHANG Yanping;HU Yu;LUO Min;CHEN Duofu(Shanghai Engineering Research Center of Hadal Science and Technology,College of Marine Sciences,Shanghai Ocean University,Shanghai 201306,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]深渊科学与技术研究中心,上海海洋大学海洋科学学院,上海201306 [2]同位素地球化学国家重点实验室,中国科学院广州地球化学研究所,广州510640

出　　处：《海洋地质与第四纪地质》2020年第3期99-108,共10页Marine Geology & Quaternary Geology

基　　金：国家重点研究发展计划冷泉重点项目“中国海域冷泉系统演变过程及其机制”(2018YFC0310003);国家自然科学基金项目“南海北部冷泉和天然气水合物发育区海底浅表层沉积物碳循环数值模拟”(41730528);“冲绳海槽海底冷泉-热液系统相互作用及资源效应”(91858208)。

摘　　要：在天然气水合物发育区海底沉积物中甲烷厌氧氧化作用(AOM)是碳循环的重要组成部分。通过定量计算表层沉积物中甲烷迁移转化通量,可以更准确评估甲烷来源碳对沉积物碳库和海洋深部碳库影响。本文利用反应―运移模型对采集于南海神狐水合物发育区两个站位(SH-W19-PC、SH-W23-PC)采集的孔隙水SO42-、溶解无机碳(DIC)、Ca2+剖面进行拟合,同时对DIC碳同位素进行分析,确定近海底沉积物中的碳循环。研究显示两个站位孔隙水中SO42-和Ca2+浓度在剖面上随深度呈线性减少,DIC浓度随深度逐渐增加,其δ13CDIC值随深度逐渐降低至约-25‰,表明两个站位存在一定程度的AOM。模拟计算两个站位沉积物孔隙水溶解甲烷向上的通量分别为25.9和18.4 mmol·m^-2 a^-1,AOM作用产生的DIC分别占其总DIC量的70.7%和60%。由沉积物向海水中释放的DIC通量占DIC汇的约60%。因此,在天然气水合物发育区向海底渗漏甲烷大部分以DIC的形式进入上覆海水,这些具有极负碳同位素值的甲烷来源的DIC可能对局部深海碳库产生一定的影响。Anaerobic oxidation of methane(AOM)is an important process in the carbon cycle in marine sediments,especially in hydratebearing areas.By quantifying the pattern of methane migration and conversion flux in surface sediments,we can assess the impact of carbon,derived from methane,onto sediment carbon pool and deep ocean carbon pool more accurately.In this research,the reaction-migration model is used to fit the SO4^2−,dissolved inorganic carbon(DIC),and Ca2+concentration of pore water and the carbon isotope of DIC is analyzed simultaneously at SH-W19-PC and SH-W23-PC Station,which are two typical hydrate-bearing areas in the Shenhu area of South China Sea.The analyzed results reveal that,the concentrations of SO42−and Ca2+in the pore water of the two stations decrease linearly with depth,while the DIC concentration increases with depth.And theδ13CDIC value of the DIC in the pore water is near-25‰,indicating methane activity in these two stations.The numerical results show that the flux of dissolved methane in the pore water of the two stations are 25.9 mmol·m^−2 a^−1 and 18.4 mmol·m^−2 a^−1,respectively.And the content of DIC produced by AOM accounts for 70.7%and 60%of the total DIC content.In addition,the DIC flux released from sediment to seawater is about 60%of the DIC sink.Therefore,methane leaking from the cold seep area and hydratebearing area enters the overlying seawater partly in the form of DIC.These methane-derived DIC with extremely negative carbon isotope values may have a certain impact on the local deep sea carbon pool.

关 键 词：天然气水合物发育区 甲烷周转 反应―运移模型 DIC源汇 碳循环 南海 

分 类 号：P736.4[天文地球—海洋地质] P738[天文地球—海洋科学]