Ice-rich permafrost has been subject to abrupt thaw and thermokarst formation in the past and is vulnerable to current global warming. The ice-rich permafrost domain includes Yedoma sediments that have never thawed since deposition during the late Pleistocene and Alas sediments that were formed by previous thermokarst processes during the Lateglacial and Holocene warming. Permafrost thaw unlocks organic carbon (OC) and minerals from these deposits and exposes OC to mineralization. A portion of the OC can be associated with iron (Fe), a redox-sensitive element acting as a trap for OC. Post-depositional thaw processes may have induced changes in redox conditions in these deposits and thereby affected Fe distribution and interactions between OC and Fe, with knock-on effects on the role that Fe plays in mediating present day OC mineralization. To test this hypothesis, we measured Fe concentrations and proportion of Fe oxides and Fe complexed with OC in unthawed Yedoma and previously thawed Alas deposits. Total Fe concentrations were determined on 1292 sediment samples from the Yedoma domain using portable X-ray fluorescence; these concentrations were corrected for trueness using a calibration based on a subset of 144 samples measured by inductively coupled plasma optical emission spectrometry after alkaline fusion (R² = 0.95). The total Fe concentration is stable with depth in Yedoma deposits, but we observe a depletion or accumulation of total Fe in Alas deposits, which experienced previous thaw and/or flooding events. Selective Fe extractions targeting reactive forms of Fe on unthawed and previously thawed deposits highlight that about 25% of the total Fe is present as reactive species, either as crystalline or amorphous oxides, or complexed with OC, with no significant difference in proportions of reactive Fe between Yedoma and Alas deposits. These results suggest that redox driven processes during past thermokarst formation impact the present-day distribution of total Fe, and thereby the total amount of reactive Fe in Alas versus Yedoma deposits. This study highlights that ongoing thermokarst lake formation and drainage dynamics in the Arctic influences reactive Fe distribution and thereby interactions between Fe and OC, OC mineralization rates, and greenhouse gas emissions.

中文翻译：

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Yedoma 域热岩溶过程中的铁重新分布

富含冰的永久冻土在过去经历过突然融化和热岩溶形成，并且容易受到当前全球变暖的影响。富含冰的永久冻土域包括自晚更新世沉积以来从未解冻的 Yedoma 沉积物和由晚冰期和全新世变暖期间先前热岩溶过程形成的 Alas 沉积物。永久冻土融化从这些沉积物中释放出有机碳 (OC) 和矿物质，并使 OC 暴露于矿化中。一部分 OC 可以与铁 (Fe) 相关联，铁是一种氧化还原敏感元素，用作 OC 的陷阱。沉积后解冻过程可能导致这些矿床中氧化还原条件发生变化，从而影响 Fe 分布以及 OC 和 Fe 之间的相互作用，对 Fe 在介导当今 OC 矿化中的作用产生连锁反应。为了验证这一假设，我们测量了未解冻的 Yedoma 和先前解冻的 Alas 矿床中的 Fe 浓度和 Fe 氧化物以及与 OC 复合的 Fe 的比例。使用便携式 X 射线荧光对来自 Yedoma 区域的 1292 个沉积物样品进行测定；使用基于碱聚变后电感耦合等离子体发射光谱法测量的 144 个样品子集（R² = 0.95）的校准，对这些浓度进行了正确性校正。Yedoma 矿床的总铁浓度随深度而稳定，但我们观察到 Alas 矿床中总铁的消耗或积累，这些矿床经历了先前的解冻和/或洪水事件。针对未解冻和先前解冻沉积物上反应性形式的 Fe 的选择性 Fe 提取突出显示，总 Fe 的约 25% 以反应性物质的形式存在，以结晶或非晶氧化物形式存在，或与 OC 复合，反应性 Fe 的比例没有显着差异Yedoma 和 Alas 矿床之间。这些结果表明，过去热岩溶形成过程中的氧化还原驱动过程会影响当今总铁的分布，从而影响 Alas 与 Yedoma 矿床中反应性铁的总量。这项研究强调，北极持续的热岩溶湖形成和排水动力学影响反应性 Fe 分布，从而影响 Fe 和 OC、OC 矿化率和温室气体排放之间的相互作用。Yedoma 和 Alas 矿床之间活性铁的比例没有显着差异。这些结果表明，过去热岩溶形成过程中的氧化还原驱动过程会影响当今总铁的分布，从而影响 Alas 与 Yedoma 矿床中反应性铁的总量。这项研究强调，北极持续的热岩溶湖形成和排水动力学影响反应性 Fe 分布，从而影响 Fe 和 OC、OC 矿化率和温室气体排放之间的相互作用。Yedoma 和 Alas 矿床之间活性铁的比例没有显着差异。这些结果表明，过去热岩溶形成过程中的氧化还原驱动过程会影响当今总铁的分布，从而影响 Alas 与 Yedoma 矿床中反应性铁的总量。这项研究强调，北极持续的热岩溶湖形成和排水动力学影响反应性 Fe 分布，从而影响 Fe 和 OC、OC 矿化率和温室气体排放之间的相互作用。