Abstract This study applies a combined isotope and doubly-substituted isotopologue (‘clumped’) methane approach to samples collected over a 9-year long-term experiment at the Kidd Creek scientific observatory located 2.4 and 2.9 km depth below surface, combined with previously published data from 2.1 km below surface. The observatory is located in a fractured rock system within Kidd Creek Mine in Timmins, Ontario, Canada, situated within a 2.7 Ga Volcanogenic Massive Sulphide (VMS) deposit on the Canadian Shield. Isotope and isotopologue methane data suggest a temporal variation in the various sources of methane within the fracture fluids system between 2.1 and 2.9 km below surface. Predominantly abiogenic methane is identified in samples collected from the deepest level of the mine (2.9 km). Comparing new data from the 2.4 km level with previous data from 2.1 km suggests addition of a small component of microbially-generated methane to the fracture water systems at 2.4 km. The temporal evolution of the methane isotopologue signatures suggest an additional process is occurring within these waters. Specifically, methane in samples from 2.4 km (and some from 2.9 km) approach low-temperature thermodynamic equilibrium in clumped isotopologue space, which is not consistent with kinetically-controlled methane production (either microbial or abiogenic). Anaerobic Oxidation of Methane (AOM) during microbial methanotrophy is shown to be the most likely process to drive such re-equilibration via isotopic bond re-ordering. This study provides an unprecedented high-resolution temporal record over more than a decade for methane in a deep subsurface crystalline environment and demonstrates the advantages of clumped isotopologue studies to identify multiple processes controlling the methane cycle in these systems including both abiotic and biotic methane production and methanotrophy.

中文翻译：

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高分辨率、长期同位素和同位素变化确定了深层地下碳循环中甲烷的来源和汇

摘要 本研究对位于地表以下 2.4 和 2.9 公里深度的 Kidd Creek 科学天文台进行 9 年长期实验收集的样品应用组合同位素和双取代同位素体（“聚集”）甲烷方法，并结合先前发表的来自地表以下 2.1 公里的数据。该天文台位于加拿大安大略省蒂明斯的 Kidd Creek 矿的裂隙岩石系统中，位于加拿大地盾上的 2.7 Ga 火山大块硫化物 (VMS) 矿床内。同位素和同位素体甲烷数据表明，地表以下 2.1 至 2.9 公里之间的压裂流体系统内的各种甲烷来源存在时间变化。在从矿井最深处（2.9 公里）收集的样本中确定了主要是非生物成因的甲烷。比较来自 2 的新数据。4 公里的水平以及 2.1 公里的先前数据表明，在 2.4 公里处的裂缝水系统中添加了一小部分微生物产生的甲烷。甲烷同位素体特征的时间演变表明，这些水域中正在发生一个额外的过程。具体而言，来自 2.4 公里（和一些来自 2.9 公里）的样品中的甲烷在聚集同位素空间中接近低温热力学平衡，这与动力学控制的甲烷生产（微生物或非生物成因）不一致。微生物甲烷营养过程中的甲烷厌氧氧化 (AOM) 被证明是最有可能通过同位素键重新排序来驱动这种重新平衡的过程。