Recently developed methane clumped isotope techniques provides fresh and novel insights into methane biogeochemistry, which have been unobtainable through other techniques such as conventional stable isotope determinations and molecular composition measurements of hydrocarbons. Nonetheless, the governing processes and mechanisms which control the clumped isotope signatures (Δ¹³CH₃D and Δ¹²CH₂D₂) of natural methane samples remain an active area of investigation. Here, we present paired clumped isotope measurements in methane hydrate, which is a major methane reservoir widely distributed along the continental margins and which plays an important role in the global carbon cycle and climate system. Our study aims to shed new light into the fundamental processes of methane clumped isotope effects and their potential to answer fundamental questions regarding the source and migration of methane found in naturally occurring gas hydrate accumulations.

Gas hydrate samples were recovered from five shallow marine sediment sites on the eastern margin of the Japan Sea and most of them present Δ¹³CH₃D and Δ¹²CH₂D₂ temperatures ranging from ∼15 to ∼170 °C that apparently match expected methane formation temperatures. The distribution of these clumped isotope signatures along the equilibrium line is best explained by the mixing effect of equilibrated thermogenic methane formed at temperatures of 165±15 °C and biogenic methane equilibrated at 1-2 °C, which may result from slow methanogenesis, anaerobic oxidation of methane (AOM), or their combination. The influences of gas migration/diffusion, hydrate formation and dissociation on Δ¹³CH₃D and Δ¹²CH₂D₂ values are insignificant. By combining clumped isotope results with other traditional approaches, a thermogenic and two microbial end-members as well as their isotopic compositions were identified and the relative contribution of each end-member was also quantified. The results not only demonstrate the applicability of methane clumped isotope data to identify potential end-members in natural methane samples, but also reveal that more traditional carbon isotope approaches may significantly underestimate the fraction of thermogenic methane present in global gas hydrate reservoirs. Improvements in the accuracy of source apportionment enable us to better understand the formation history and mechanisms of gas hydrate accumulation, as well as the role played by gas hydrate dissociation in past geological events. The estimated formation temperatures of thermogenic end-member can be further applied in reconstruction of the paleo geothermal gradient at the time when the thermogenic methane was formed at marine sedimentary environment.

最近开发的甲烷聚集同位素技术提供了对甲烷生物地球化学的新鲜和新颖的见解，这是通过其他技术无法获得的，例如传统的稳定同位素测定和碳氢化合物的分子组成测量。尽管如此，控制聚集同位素特征（Δ ¹³ CH ₃ D 和Δ ¹² CH ₂ D ₂) 的天然甲烷样品仍然是一个活跃的研究领域。在这里，我们介绍了甲烷水合物的成对成簇同位素测量，甲烷水合物是一个主要的甲烷储层，广泛分布于大陆边缘，在全球碳循环和气候系统中起着重要作用。我们的研究旨在揭示甲烷聚集同位素效应的基本过程及其在回答天然天然气水合物聚集中发现的甲烷来源和迁移的基本问题的潜力。

从日本海东缘的五个浅海沉积地点回收了天然气水合物样品，其中大部分的 Δ ¹³ CH ₃ D 和 Δ ¹² CH ₂ D ₂温度范围从 ~15 到 ~170 °C，显然与预期相符甲烷形成温度。这些聚集的同位素特征沿平衡线的分布最好通过在 165±15 °C 温度下形成的平衡产热甲烷和在 1-2 °C 平衡的生物甲烷的混合效应来解释，这可能是由于缓慢的产甲烷作用、厌氧甲烷氧化 (AOM) 或其组合。气体运移/扩散、水合物形成和解离对Δ ¹³ CH的影响₃ D 和 Δ ¹² CH ₂ D ₂值是微不足道的。通过将成簇同位素结果与其他传统方法相结合，确定了一种产热和两种微生物端元及其同位素组成，并量化了每个端元的相对贡献。结果不仅证明了甲烷成簇同位素数据在识别天然甲烷样品中潜在的末端成员方面的适用性，而且还揭示了更传统的碳同位素方法可能会大大低估全球天然气水合物储层中存在的热成因甲烷的比例。源解析精度的提高使我们能够更好地了解天然气水合物的形成历史和成藏机制，以及天然气水合物分解在过去地质事件中所起的作用。