The sulfur cycle below the sulfate-methane transition of marine sediments
The sulfur cycle below the sulfate-methane transition of marine sediments
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DOI：
10.1016/j.gca.2018.07.027
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发表时间：
2018-10
影响因子：
5
通讯作者：
André Pellerin;G. Antler;H. Røy;A. Findlay;F. Beulig;Caroline Scholze;A. Turchyn;B. Jørgensen
中科院分区：
文献类型：
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作者：
André Pellerin;G. Antler;H. Røy;A. Findlay;F. Beulig;Caroline Scholze;A. Turchyn;B. Jørgensen
海洋沉积物中硫酸盐还原至硫酸盐-甲烷转变 (SMT) 以下的研究需要采取严格的预防措施，以避免海水硫酸盐或处理过程中硫化物氧化造成的硫酸盐污染。我们尝试了不同的孔隙水硫酸盐取样方法，发现对取样程序的修改将测量的硫酸盐浓度从数百微摩尔降低到十微摩尔或更低。我们在此建议对孔隙水采样进行一些关键修改，以避免污染或氧化伪影，例如在测量低于海洋沉积物 SMT 的极低硫酸盐浓度时。在奥胡斯湾的三个地点，低于 SMT 的硫酸盐浓度保持在 10 微摩尔左右。计算出的自由能变化 ΔGr 可用于如此低浓度的硫酸盐还原，介于 -17.9 和 -11.9kJmol−1 硫酸盐之间。这接近或低于之前计算的海洋沉积物中微生物硫酸盐还原的能量产量。这三个地点的特点是硫酸盐还原率可测量且差异很大，具体取决于 SMT 的深度和沉积年龄。我们的数据显示，尽管硫酸盐浓度较低，硫酸盐的消耗却低于 SMT。由于硫酸盐不会降低到更低的浓度，因此必须在 SMT 以下持续再生，最有可能是通过 Fe(III) 驱动的硫化物氧化与硫酸盐还原同时发生。我们得出的结论是，低亚 SMT 硫酸盐浓度在还原和生产之间处于稳定状态，并且由硫酸盐还原细菌的最小 ΔGr 要求进行热力学控制，而硫酸盐还原速率由硫化物氧化速率控制。这项研究涉及未受污染的孔隙水的一般取样，并提示了取芯和孔隙水提取引起的孔隙水污染水平较低的系统性问题。在 SMT 以下，可以检测到这种污染，但在 SMT 以上则不会被注意到。本研究中观察到的低水平污染可能会影响孔隙水中的其他低浓度或氧化还原敏感元素。
The study of sulfate reduction below the sulfate-methane transition (SMT) in marine sediments requires strict precautions to avoid sulfate contamination from seawater sulfate or from sulfide oxidation during handling. We experimented with different methods of sampling porewater sulfate and found that modifications to our sampling procedure reduced the measured sulfate concentrations from hundreds of micromolar to ten micromolar or less. We here recommend some key modifications to porewater sampling to avoid contamination or oxidation artifacts, for example when measuring very low sulfate concentrations below the SMT of marine sediments. At three sites in Aarhus Bay, the sulfate concentrations below the SMT remained around ten micromolar. The calculated free energy change, ΔGr, available for sulfate reduction by such low concentrations is between −17.9 and −11.9 kJ mol−1sulfate. This is near or below the energy yields that have previously been calculated for microbial sulfate reduction in marine sediments. The three sites are characterized by measurable and very different sulfate reduction rates depending on the depth and sediment age of the SMT. Our data show that sulfate is being consumed below the SMT in spite of the low sulfate concentrations. As sulfate is not drawn down to even lower concentrations, it must be continually regenerated below the SMT, most likely by Fe(III)-driven sulfide oxidation concurrent with the sulfate reduction. We conclude that the low sub-SMT sulfate concentrations are in steady state between reduction and production and are thermodynamically controlled by the minimum ΔGrrequirements by sulfate reducing bacteria while sulfate reduction rates are controlled by the rate of sulfide oxidation. This study deals with the general sampling of uncontaminated pore water and hints to a systemic problem with low levels of contamination in porewater induced by coring and pore water extraction. Below the SMT, this contamination could be detected but above the SMT it goes unnoticed. Low levels of contamination as observed in this study may affect other low concentration or redox-sensitive elements in pore water.