Pore-water dissolved inorganic carbon sources and cycling in the shallow sediments of the Haima cold seeps, South China Sea
Pore-water dissolved inorganic carbon sources and cycling in the shallow sediments of the Haima cold seeps, South China Sea
复制标题
南海海马冷泉浅层沉积物孔隙水溶解无机碳源及其循环
DOI：
10.1016/j.jseaes.2020.104495
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发表时间：
2020-10-01
影响因子：
3
通讯作者：
Wang, Yiqing
中科院分区：
文献类型：
--
作者：
Liu, Weining;Wu, Zijun;Wang, Yiqing
孔隙水的地球化学组成提供了海底冷泉活动和沉积物中甲烷碳的生物地球化学过程的信息。在本研究中，通过载人潜水器在活动的海马冷泉中心和边缘以及附近的背景场地采集了6个沉积物推进岩芯。测定了各沉积物柱样中SO42-、Ca~(2+)、Mg~(2+)、Sr~(2+)、NH_4~(4+)、溶解无机碳(DIC)和三角洲C-13-DIC的孔隙水组成。硫酸盐-甲烷过渡带(SMTZ)的极浅层表明，浅层沉积物中存在高甲烷通量和显著的厌氧甲烷氧化(AOM)活动。反应输运模拟结果表明，AOM和有机碎屑硫酸盐还原(OSR)消耗硫酸盐的相对贡献率在HM-2-6站点分别为84.1%和15.9%，在HM-3-3站点分别为94.6%和5.4%。此外，在中心位置HM-2-6(-45.67‰)和HM-3-3(-53.87‰)的极低的C-13-DIC值指示外部甲烷来源的DIC。根据三角洲C-13质量平衡，我们量化了HM-2-6和HM-3-3的有机质降解产生的孔隙水DIC和AOM的比例分别为24.7%和65.3%，9.3%和80.7%。孔隙水DIC浓度的增加会导致碳酸盐的析出。锶/钙与镁/钙比值图解表明，该区沉积物中的碳酸盐相以高镁方解石为主。我们的研究表明，AOM可以作为主要的生物地球化学过程，通过将甲烷衍生的碳结合到溶解和固体无机碳相中，显著影响海马冷渗区浅层沉积物中的DIC循环。
Pore-water geochemical compositions provide the insights into seafloor cold seep activities and biogeochemical processes of methane-derived carbon in sediments. In this study, six sediment push cores were collected by manned submersible at the center and edge of the active Haima cold seeps, and a nearby background site. Pore-water compositions of the SO42-, Ca2+, Mg2+, Sr2+, NH4+, dissolved inorganic carbon (DIC), and delta C-13-DIC at each sediments core were measured. The very shallow depths of sulfate-methane transition zone (SMTZ) suggest that high methane flux and significant anaerobic oxidation of methane (AOM) activities occur in the shallow sediments. Reaction-transport modelling results show that the relative contributions of AOM and organoclastic sulfate reduction (OSR) consuming sulfate are 84.1% and 15.9% at site HM-2-6, and 94.6% and 5.4% at site HM-3-3, respectively. Furthermore, extremely low delta C-13-DIC values at the central sites HM-2-6 (-45.67 parts per thousand) and HM-3-3 (-53.87 parts per thousand) indicate an external methane-derived DIC. Based on the delta C-13 mass balance, we quantify the proportions of pore-water DIC derived from organic matter degradation and AOM as 24.7% and 65.3% at site HM-2-6, and 9.3% and 80.7% at site HM-3-3, respectively. An increase in pore-water DIC concentration leads to carbonate precipitation. Plots of Sr/Ca vs. Mg/Ca ratios reveal that the carbonate phases in sediments are dominantly high Mg-calcite in this region. Our study demonstrates that AOM can serve as a dominant biogeochemical process through incorporation of methane-derived carbon into dissolved and solid inorganic carbon phases, significantly influencing DIC cycling within the shallow sediments of the Haima cold seep area.