The impact of diffusive transport of methane on pore-water and sediment geochemistry constrained by authigenic enrichments of carbon, sulfur, and trace elements: A case study from the Shenhu area of the South China Sea
The impact of diffusive transport of methane on pore-water and sediment geochemistry constrained by authigenic enrichments of carbon, sulfur, and trace elements: A case study from the Shenhu area of the South China Sea
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碳、硫和微量元素自生富集约束下甲烷扩散迁移对孔隙水和沉积物地球化学的影响——以南海神狐海域为例
DOI：
10.1016/j.chemgeo.2020.119805
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发表时间：
2020-10
期刊：
影响因子：
3.9
通讯作者：
Duofu Chen
中科院分区：
文献类型：
--
作者：
Yu Hu;Dong Feng;Jörn Peckmann;Shanggui Gong;Qianyong Liang;Hongbin Wang;Duofu Chen
硫酸盐驱动的甲烷厌氧氧化（SD-AOM）控制甲烷从海洋沉积物释放到海洋。沉积物中的各种自生沉淀物已被广泛用于识别过去发生的SD-AOM。然而，缺乏对这些沉淀物形成条件的系统评价，有时会阻碍在过去以甲烷扩散输送为特征的环境中识别SD-AOM。研究了南海神狐海域甲烷向上扩散影响点孔隙水和沉积物的碳、硫和微量元素地球化学特征。根据硫酸盐和甲烷浓度，这里的硫酸盐-甲烷过渡带（SMTZ）位于海底以下约7.6 m处。硫酸盐δ34S与δ18O值的斜率与甲烷扩散输运相一致。孔隙水种类的浓度和同位素剖面表明溶质是扩散输送而不是平流输送。根据硫酸盐δ34S值推断，硫酸盐还原作用增强，与本地赋存相对丰富、富34s的硫化铁矿物一致。根据硫化铁矿物的数量和目前硫酸盐的扩散通量，估计在SMTZ周围产生自生硫化铁所需的时间为~1.1 ka。沉积物中未发现自生碳酸盐、钡（Ba）和钼（Mo）富集。这一观察结果与孔水中钙、镁、钡和钼的电流通量太低而不能进行自生富集的计算是一致的。低通量主要受扩散控制，有利于富34s硫化铁矿物的形成。与受平流渗流影响的沉积物不同，观察到的富集模式预计在现代和古代大陆边缘沉积物中普遍存在，并可能有助于识别地质记录中过去的甲烷富带和上覆的SD-AOM带作为甲烷汇。
Sulfate-driven anaerobic oxidation of methane (SD-AOM) controls methane release from marine sediments to the ocean. A variety of authigenic precipitates within sediments has been widely used to identify past occurrences of SD-AOM. However, the lack of a systematic evaluation of the formation conditions of these precipitates sometimes impedes the recognition of SD-AOM in past environments characterized by diffusive transport of methane. Carbon, sulfur, and trace element geochemistry of pore-water and sediments was investigated at a site affected by upward methane diffusion in the Shenhu area of the South China Sea. Here, the sulfate-methane transition zone (SMTZ) is located ~7.6 m below the seafloor based on sulfate and methane concentrations. The slope of δ34S vs. δ18O values of sulfate is consistent with diffusive transport of methane. Concentration and isotope profiles of pore-water species point to diffusive rather than advective transport of solutes. Enhanced sulfate reduction inferred from δ34S values of sulfate agrees with the local occurrence of relatively abundant,34S-enriched iron sulfide minerals. The time required to produce the observed authigenic iron sulfides around the SMTZ is estimated to be ~1.1 ka based on the amount of iron sulfide minerals and the present diffusive flux of sulfate. No enrichment of authigenic carbonate, barium (Ba), and molybdenum (Mo) was detected in the studied sediments. This observation is consistent with the calculation that the current fluxes of pore-water calcium, magnesium, Ba, and Mo are too low to allow for authigenic enrichments. The low fluxes are largely controlled by diffusion, which facilitates the formation of34S-enriched iron sulfide minerals. The observed enrichment patterns – unlike those of sediments affected by advective seepage – are expected to be prevalent in modern and ancient continental-margin sediments, and may contribute to the identification of past methane-rich zones and overlying SD-AOM zones as sinks for methane in the geological record.
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影响因子：
3.7
作者：
A. Peketi;A. Mazumdar;H. M. Joao;D. J. Patil;A. Usapkar;P. Dewangan
通讯作者：
A. Peketi;A. Mazumdar;H. M. Joao;D. J. Patil;A. Usapkar;P. Dewangan
影响因子：
5.3
作者：
W. Ussler;C. Paull
通讯作者：
W. Ussler;C. Paull
影响因子：
5
作者：
Brunner, B;Bernasconi, SM;Schroth, MH
通讯作者：
Schroth, MH
影响因子：
2.9
作者：
Kerstin Nöthen;S. Kasten
通讯作者：
Kerstin Nöthen;S. Kasten
影响因子：
3.7
作者：
A. Peketi;A. Mazumdar (corresponding author);R. K. Joshi;D. J. Patil;P. L. Srinivas;A. M. Dayal
通讯作者：
A. Peketi;A. Mazumdar (corresponding author);R. K. Joshi;D. J. Patil;P. L. Srinivas;A. M. Dayal