Abstract Understanding landscape evolution on geological time scales has become increasingly important in the light of recent climate warming and intensified land use. Uranium isotopes ((234U/238U) activity ratios) can be used to reconstruct catchment-wide erosion from fine-grained detrital matter, as the lighter nuclide 234U is lost from grains Loss of 234U is mainly attributed to recoil of 234Th during α-decay of 238U. However, mobilisation of 234U is also controlled by preferential oxidation and leaching of 234U from detrital grains. Further considerations are required concerning the sediment mineralogy and uranium bound to authigenic or endogenic matter. Here, we extend the discussion about the controls on previously published (234U/238U) activity ratios and uranium concentrations of detrital matter along a 5.43 m-long, Late Glacial to Holocene sedimentary record from Lake Ohrid (North Macedonia, Albania). Lake Ohrid is chosen to study how erosion responds to anthropogenic disturbances and climate variability, which are common through the Late Pleistocene and Holocene in the Mediterranean Region. We compared uranium concentration and isotope data to redox-sensitive, mineralogical and biogeochemical proxies. Mineralogical and biogeochemical data show no control on uranium concentration and (234U/238U) activity ratios. Rock magnetic redox proxies indicate uranium mobilisation from detrital matter in more oxic environments. No correlation between (234U/238U) activity ratios and rock magnetic data is observed, which implies that the redox environment has no control on the isotope signal. Monte Carlo simulations reveal that post-depositional preferential mobilisation of 234U has only negligible impact on the calculated sediment residence times. Our model implies that pre-depositional leaching can results in shorter sediment residence times but low (234U/238U) activity ratios during cold and dry intervals imply that recoil is likely the main processes explaining loss of 234U from the detrital grain. This is explained by the time scales studied herein in (>10,000 years), during which preferential leaching is seen to be not significant.

中文翻译：

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对碎屑湖相沉积物中记录的 (234U/238U) 活度比的控制评估

摘要 鉴于近期气候变暖和土地利用的加剧，了解地质时间尺度上的景观演变变得越来越重要。铀同位素（（234U/238U）活度比）可用于从细粒碎屑物质重建流域范围内的侵蚀，因为较轻的核素 234U 从颗粒中损失 234U 的损失主要归因于 α 衰变期间 234Th 的反冲238U。然而，234U 的移动也受到 234U 从碎屑颗粒的优先氧化和浸出控制。需要进一步考虑沉积物矿物学和与自生或内生物质结合的铀。在这里，我们扩展了对先前公布的 (234U/238U) 活度比和碎屑物质铀浓度的控制的讨论，沿 5.43 m 长，奥赫里德湖（北马其顿，阿尔巴尼亚）的晚冰期至全新世沉积记录。选择奥赫里德湖来研究侵蚀如何对人为干扰和气候变化做出反应，这在地中海地区的晚更新世和全新世中很常见。我们将铀浓度和同位素数据与氧化还原敏感、矿物学和生物地球化学代理进行了比较。矿物学和生物地球化学数据显示对铀浓度和 (234U/238U) 活度比没有控制。岩石磁性氧化还原代理表明铀从更多含氧环境中的碎屑中动员。未观察到 (234U/238U) 活动比与岩石磁数据之间的相关性，这意味着氧化还原环境无法控制同位素信号。蒙特卡罗模拟表明，234U 的沉积后优先动员对计算的沉积物停留时间的影响可以忽略不计。我们的模型意味着沉积前浸出可以导致更短的沉积物停留时间，但在寒冷和干燥间隔期间的低 (234U/238U) 活动比意味着反冲可能是解释碎屑颗粒中 234U 损失的主要过程。这可以通过本文研究的时间尺度（> 10,000 年）来解释，在此期间优先浸出被认为不显着。我们的模型意味着沉积前浸出可以导致更短的沉积物停留时间，但在寒冷和干燥间隔期间的低 (234U/238U) 活动比意味着反冲可能是解释碎屑颗粒中 234U 损失的主要过程。这可以通过本文研究的时间尺度（> 10,000 年）来解释，在此期间优先浸出被认为不显着。我们的模型意味着沉积前浸出可以导致更短的沉积物停留时间，但在寒冷和干燥间隔期间的低 (234U/238U) 活动比意味着反冲可能是解释碎屑颗粒中 234U 损失的主要过程。这可以通过本文研究的时间尺度（> 10,000 年）来解释，在此期间优先浸出被认为不显着。