Rates of anaerobic oxidation of methane and authigenic carbonate mineralization in methane-rich deep-sea sediments inferred from models and geochemical profiles
Rates of anaerobic oxidation of methane and authigenic carbonate mineralization in methane-rich deep-sea sediments inferred from models and geochemical profiles
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DOI：
10.1016/j.epsl.2007.10.056
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发表时间：
2008-02
影响因子：
5.3
通讯作者：
W. Ussler;C. Paull
中科院分区：
文献类型：
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作者：
W. Ussler;C. Paull
从墨西哥湾北方（北纬28°04.00′，西经89°43.15′）水深647 m处富含甲烷的沉积物中采集的10.5 m长的巨型重力岩心中获得的孔隙水化学数据，以前所未有的详细程度确定了海底下梯度。该岩心穿透了海底下300厘米处的硫酸盐-甲烷界面（SMI）。在SMI，溶解无机碳（DIC）浓度达到最大值（13.5 mM），孔隙水δ 13 C DIC（−63.2‰ PDB）和δ 13 C甲烷（−89.5‰ PDB）值最负。SMI孔隙水硫酸盐几乎耗尽，甲烷浓度急剧上升，同时出现气泡结构沉积物，细粒甲烷衍生自生碳酸盐结核和胶结物是常见的。DIC浓度和同位素值的尖峰集中在SMI表明，DIC是由甲烷厌氧氧化（AOM）在一个狭窄的区域内以SMI为中心。详细的硫酸盐和DIC浓度剖面以及DIC δ 13 C值使得能够构建地球化学模型，以探索AOM形成DIC的速率及其对孔隙水DIC δ 13 C值的影响。模型结果与测得的DIC浓度和δ 13 C同位素分布密切匹配，表明甲烷碳向DIC的微生物转化在地质学上是迅速的，AOM发生在SMI的当前位置。在现今SMI之下发现的自生碳酸盐的同位素值（δ 13 C =−60.2±0.7‰ PDB，440立方英尺/平方英尺）与在以前SMI的位置通过AOM从甲烷衍生碳酸盐碳的结果一致。这些观测和模型结果表明，AOM发生的速率将产生观测到的配置文件，并开始沉淀甲烷衍生的碳酸盐发生在几个世纪的时间尺度。模型结果还表明，所需的时间产生的自生水泥是一个数量级大于AOM产生所观察到的DIC配置文件。DIC生产AOM的代谢率推断从建模的地球化学配置文件比较有利，从实验室微生物培养和放射性标记的示踪剂实验获得的速率数据。
Pore water chemical data obtained from a 10.5-m long giant gravity core collected in methane-rich sediments from 647 m water depth in the northern Gulf of Mexico (N 28°04.00′ W 89°43.15′) defines sub-bottom gradients in unprecedented detail. This core penetrated the sulfate-methane interface (SMI) at ∼300 cm below the seafloor (cmbsf). At the SMI dissolved inorganic carbon (DIC) concentrations reach a maximum (13.5 mM) and pore water δ13C DIC (−63.2‰ PDB) and δ13C methane (−89.5‰ PDB) values are most negative. Below the SMI pore water sulfate is nearly depleted, methane concentrations rise sharply with simultaneous occurrence of a bubble-textured sediment, and fine-grained methane-derived authigenic carbonate nodules and cements are common. The sharp peaks in DIC concentration and isotope values centered at the SMI indicate that DIC is being produced by anaerobic oxidation of methane (AOM) within a narrow zone centered at the SMI. The detailed sulfate and DIC concentration profiles, and DIC δ13C values have enabled geochemical models to be constructed that explore the rate of DIC formation by AOM and its effect on pore water DIC δ13C values. Model results closely match measured DIC concentration and δ13C isotope profiles and indicate that microbiological conversion of methane carbon to DIC is rapid in geologic terms and that AOM is occurring at the present position of the SMI. Isotope values for authigenic carbonate found immediately below the present-day SMI (δ13C=−60.2±0.7‰ PDB at 440 cmbsf) are consistent with derivation of the carbonate carbon from methane via AOM at the former location of a SMI. These observations and model results suggest that AOM is occurring at rates that would generate the observed profiles and begin the precipitation of methane-derived carbonate occur on time-scales of centuries. Model results also show that the time needed to produce the resulting authigenic cements is an order of magnitude greater than that for AOM to produce the observed DIC profiles. The metabolic rates for DIC production by AOM inferred from modeling the geochemical profiles compare favorably with available rate data obtained from laboratory microbial incubations and radiolabeled tracer experiments.