Chocolate Pots hot spring (CP) is an Fe-rich, circumneutral-pH geothermal spring in Yellowstone National Park. Relic hydrothermal systems have been identified on Mars, and modern hydrothermal environments such as CP are useful for gaining insight into potential pathways for generation of biosignatures of ancient microbial life on Earth and Mars. Fe isotope fractionation is recognized as a signature of dissimilatory microbial iron oxide reduction (DIR) in both the rock record and modern sedimentary environments. Previous studies in CP have demonstrated the presence of DIR in vent pool deposits and show aqueous-/solid-phase Fe isotope variations along the hot spring flow path that may be linked to this process. In this study, we examined the geochemistry and stable Fe isotopic composition of spring water and sediment core samples collected from the vent pool and along the flow path, with the goal of evaluating whether Fe isotopes can serve as a signature of past or present DIR activity. Bulk sediment Fe redox speciation confirmed that DIR is active within the hot spring vent pool sediments (but not in more distal deposits), and the observed Fe isotope fractionation between Fe(II) and Fe(III) is consistent with previous studies of DIR-driven Fe isotope fractionation. However, modeling of sediment Fe isotope distributions indicates that DIR does not produce a unique Fe isotopic signature of DIR in the vent pool environment. Because of rapid chemical and isotopic communication between the vent pool fluid and sediment, sorption of Fe(II) to Fe(III) oxides would produce an isotopic signature similar to DIR despite DIR-driven generation of large quantities of isotopically light solid-associated Fe(II). The possibility exists, however, for preservation of specific DIR-derived Fe(II) minerals such as siderite (which is present in the vent pool deposits), whose isotopic composition could serve as a long-term signature of DIR in relic hot spring environments.

中文翻译：

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黄石国家公园巧克力罐温泉异化微生物铁还原的地球化学和稳定铁同位素分析。

Chocolate Pots 温泉 (CP) 是黄石国家公园内富含铁、pH 值呈中性的地热温泉。已在火星上发现了遗迹热液系统，而现代热液环境（如 CP）可用于深入了解地球和火星上古代微生物生命生物特征产生的潜在途径。Fe同位素分馏被认为是岩石记录和现代沉积环境中异化微生物氧化铁还原（DIR）的标志。先前在 CP 中的研究已经证明了排放池沉积物中 DIR 的存在，并表明沿着温泉流动路径的水相/固相 Fe 同位素变化可能与此过程有关。在这项研究中，我们检查了从通风池和沿流动路径收集的泉水和沉积物核心样本的地球化学和稳定的 Fe 同位素组成，目的是评估 Fe 同位素是否可以作为过去或现在 DIR 活动的特征。大量沉积物 Fe 氧化还原形态证实 DIR 在温泉喷口池沉积物中是活跃的（但不是在更远的沉积物中），并且观察到的 Fe(II) 和 Fe(III) 之间的 Fe 同位素分馏与先前的 DIR 研究一致驱动铁同位素分馏。然而，沉积物 Fe 同位素分布的建模表明，DIR 在通风池环境中不会产生 DIR 的独特 Fe 同位素特征。由于排放池流体和沉积物之间的快速化学和同位素交流，Fe(II) 吸附到 Fe(III) 氧化物会产生类似于 DIR 的同位素特征，尽管 DIR 驱动产生了大量同位素轻固体相关的 Fe(II)。然而，存在保存特定 DIR 衍生的 Fe(II) 矿物的可能性，例如菱铁矿（存在于喷口池沉积物中），其同位素组成可以作为遗迹温泉环境中 DIR 的长期特征.