南海北部陆坡沉积物"Ba峰"及其天然气水合物分解指示意义

孟宪伟; 张俊; 夏鹏

南海北部陆坡沉积物"Ba峰"及其天然气水合物分解指示意义

国家海洋局第一海洋研究所,山东青岛 266061

基金项目: 国家自然科学基金(40776033)；天然气水合物环境效应研究项目(118-03)。

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- 收稿日期: 2013-01-23

Barium fronts in core sediments from northern slope of the South China Sea and its implication for decomposition of gas hydrate

First Institute of Oceanography,State Oceanic Administration,Qingdao 266061,China

摘要

摘要: 深海，特别是天然气水合物区的沉积物-孔隙水体系中，Ba循环受到孔隙水中的硫酸盐(SO²₄^-)和甲烷(CH₄)之间的氧化还原反应的强烈制约。沉积物中"Ba峰"的存在体现了SO^2-₄亏损的长时间累积效应，并与海平面变化制约下的天然气水合物分解有关。南海北部陆坡ODP1146站钻孔上部深度185 m沉积物中发育了4个"Ba峰"，其中发育于深度约58 m的"Ba峰"(F3)与当前SO^2-₄-CH₄反应界面(SMI)深度一致，推断其他3个"Ba峰"(F1、F2和F4)对应的SMI深度分别约为24 m、46 m和84 m。"Ba峰"最大峰值与沉积物Cl通量减小和冰期-间冰期转换带的对应性表明：在冰期，海平面大幅度降低诱发的浅水区(如东沙群岛附近)天然气水合物的分解持续释放了低盐度、高浓度CH₄流体，其中部分流体迁移至ODP1146站所在的陆坡区沉积物中，导致了间隙水中SO^2-₄的持续亏损和自生Ba的长时间累积，结果在冰期-间冰期转换阶段形成显著的"Ba峰";同时，部分逸散于大气中的CH₄加快了冰期的结束。在距今约50万年的冰期-间冰期旋回制约下的海平面周期性变化过程中，南海北部浅水区天然气水合物分解释放的低盐度和高浓度CH₄流体也间歇地迁移至深水陆坡沉积区，导致了多个"Ba峰"的形成和沉积埋藏。"Ba峰"可以用于评价历史时期南海北部陆坡天然气水合物分解释放甲烷通量的变化。
- 南海北部陆坡 /
- Ba循环 /
- Ba峰 /
- 甲烷水合物分解 /
- 冰期-间冰期旋回
Abstract: Barium cycling in deep-sea sediments,especially those of the areas where gas hydrate occurs,is controlled by redox between sulfate and methane within a sediment-interstitial water system. "Barium fronts" occurring in deep-sea sediments,therefore,are generally related to decomposition of gas hydrate. 4 "Barium fronts" were recognised from sediments of upper section (0-185 m). Each of them exactly corresponded to sulfate-methane interface,decrease in chlorin flux and glacial-interglacial transition,indicating that during glacial ages,gas hydrate in shallow regions,such as Dongsha Archipelago seabed would decompose due to decease in sea level stands,releasing fluids lower salinity and higher methane concentration. Some of the released fluid would laterally migrate into ODP1146 site,resulting in sulfate depletion to zero and excess barium accumulation to maximum at glacial terminations; meanwhile,some of the released fluid would migrate into air,accelerating glacial age end due to greenhouse effect of methane. Impacted by glacial-interglacial cycles over the past 500 ka,the fluids with lower salinity and higher methane,released by decomposition of gas hydrate from shallow areas,such as Dongsha archipelago,would vary in oscillatory way,resulting in burying of multiple "barium fronts" in sediments. The "barium fronts" can be used as a proxy for assesment of variation in methane flux released by decomposition of gas hydrate.
- northern slope of the South China Sea /
- barium cycling /
- barium front /
- decomposition of gas hydrate /
- glacial-interglacial cycle

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参考文献(26)

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