Anaerobic oxidation of methane and trace-element geochemistry in microbial mat-covered sediments related to methane seepage, northeastern Japan Sea
Anaerobic oxidation of methane and trace-element geochemistry in microbial mat-covered sediments related to methane seepage, northeastern Japan Sea
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DOI：
10.1016/j.chemgeo.2022.121093
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发表时间：
2022-09
期刊：
影响因子：
3.9
通讯作者：
Y. Ota;M. Suzumura;A. Tsukasaki;A. Suzuki;K. Yamaoka;M. Asada;M. Satoh
中科院分区：
文献类型：
--
作者：
Y. Ota;M. Suzumura;A. Tsukasaki;A. Suzuki;K. Yamaoka;M. Asada;M. Satoh
我们评估了与日本海东部坂田小丘（称为坂田小丘）甲烷渗漏相关的地球化学特征的空间变异性，包括微量元素循环。通过遥控车辆进行的海底观测以及通过光学测绘设备对坂田丘周围的环境进行可视化显示，丘顶部凹陷处的沉积物上覆盖着大片白色和灰色的微生物垫。推芯样品是在微生物垫内部和外部几米处以及含天然气水合物区域外部采集的。对于这些岩心，分析了间隙硫酸根离子 (SO42−) 浓度、沉积物总有机碳、总硫 (TS) 和微量元素含量以及散装碳酸盐矿物 δ13C。在微生物垫下方的整个岩心样本以及微生物垫外 10 cm 深度以下的沉积物中，TS 含量显着高于参考位点的 TS 含量，并且大块碳酸盐矿物 δ13C 呈强负值（-20‰ 至 -40‰）。这些结果表明，缺氧沉积物中硫化物矿物和自生碳酸盐的形成是通过甲烷的微生物厌氧氧化（AOM）与硫酸盐还原相结合而形成的。尽管微生物垫内部收集的沉积物中间隙水 SO42− 浓度快速线性下降支持 AOM 的发生，但微生物垫外部 SO42− 浓度没有下降，这可能是由于微生物垫内部的甲烷气体向上流量高于微生物垫外部的上升流量。 Sakata Knoll 受 AOM 影响的沉积物的特点是 Mo 和 As 富集，与 TS 含量和自生铁组分密切相关，并且自生 Mo 相对于 U 强烈富集，这表明 Mo/U 比高于海水。这些观察结果表明，Mo 和 As 通过水柱中吸附 Mo 和 As 的铁-锰羟基氧化物颗粒的沉淀，有效地从水柱转移到 Sakata Knoll 受 AOM 影响的硫化物沉积物中。
We evaluated the spatial variability of geochemical features, including trace-element cycles, associated with methane seepage in a knoll off Sakata (called Sakata Knoll) in the eastern Japan Sea. Seafloor observations from a remotely operated vehicle and environmental visualization around Sakata Knoll by an optical mapping device revealed large patches of white and gray microbial mats covering sediment in the depression on the top of the knoll. Push core samples were collected inside and a few meters outside microbial mats, and outside the gas hydrate-bearing areas. For these cores, the interstitial sulfate ion (SO42−) concentrations, sedimentary total organic carbon, total sulfur (TS), and trace-element contents, and bulk carbonate minerals δ13C were analyzed. In the entire core samples below the microbial mats and in sediments below 10 cm depth outside microbial mats, TS contents were substantially higher than those at the reference site, and bulk carbonate minerals δ13C was strongly negative (−20‰ to −40‰). These results imply that the formations of sulfide minerals and authigenic carbonates occur in the anoxic sediments via microbial anaerobic oxidation of methane (AOM) coupled with sulfate reduction. Although a rapid and linear decrease of interstitial water SO42−concentration in the sediments collected inside microbial mats supports the occurrence of AOM, there is no fall in SO42−concentration outside microbial mats, which may be explained by the higher upward flow of methane gas inside than outside the mats. The AOM-impacted sediments at Sakata Knoll were characterized by enrichments in Mo and As that were well correlated with TS contents and the authigenic iron fraction, and by strong enrichment of authigenic Mo relative to U, indicated by higher Mo/U ratios than those of seawater. These observations suggest that Mo and As are effectively transferred from the water column to AOM-impacted sulfidic sediments at Sakata Knoll via precipitation of particulate iron–manganese oxyhydroxides in the water column that have adsorbed Mo and As.