Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
Department of Earth Sciences, University of Toronto, Toronto, ON, Canada.
Nat Commun. 2024 Oct 23;15(1):9130. doi: 10.1038/s41467-024-53438-4.
The deep continental crust represents a vast potential habitat for microbial life where its activity remains poorly constrained. Organic acids like acetate are common in these ecosystems, but their role in the subsurface carbon cycle - including the mechanism and rate of their turnover - is still unclear. Here, we develop an isotope-exchange 'clock' based on the abiotic equilibration of H-isotopes between acetate and water, which can be used to define the maximum in situ acetate residence time. We apply this technique to the fracture fluids in Birchtree and Kidd Creek mines within the Canadian Precambrian crust. At both sites, we find that acetate residence times are <1 million years and calculated a rate of turnover that could theoretically support microbial life. However, radiolytic water-rock reactions could also contribute to acetate production and degradation, a process that would have global relevance for the deep biosphere. More broadly, our study demonstrates the utility of isotope-exchange clocks in determining residence times of biomolecules with possible applications to other environments.
深部大陆地壳代表了微生物生命的巨大潜在栖息地，但其活动仍受到很大限制。在这些生态系统中，乙酸等有机酸很常见，但它们在地下碳循环中的作用——包括它们转化的机制和速率——仍不清楚。在这里，我们开发了一种基于乙酸和水之间 H 同位素非生物平衡的同位素交换“时钟”，可用于定义原位乙酸居留时间的最大值。我们将该技术应用于加拿大前寒武纪地壳中的 Birchtree 和 Kidd Creek 矿的裂缝流体中。在这两个地点，我们发现乙酸居留时间<100 万年，计算出的周转率理论上可以支持微生物生命。然而，放射分解水-岩反应也可能有助于乙酸的产生和降解，这一过程对深部生物圈具有全球意义。更广泛地说，我们的研究表明，同位素交换时钟在确定生物分子居留时间方面具有实用性，可能适用于其他环境。
