Abstract Although the oxygen isotope composition (δ18O) of calcite (δ18Ocalcite) and, to a lesser extent, diatom silica (δ18Odiatom) are widely used tracers of past hydroclimates (especially temperature and surface water hydrology), the degree to which these two hosts simultaneously acquire their isotope signals in modern lacustrine environments, or how these are altered during initial sedimentation, is poorly understood. Here, we present a unique dataset from a natural limnological laboratory to explore these issues. This study compares oxygen and hydrogen isotope data (δ18O, δ2H) of contemporary lake water samples at ~2-weekly intervals over a 2-year period (2010–12) with matching collections of diatoms (δ18Odiatom) and calcite (δ18Ocalcite) from sediment traps (at 10 m and 25 m) at Rostherne Mere (maximum depth 30 m), a well-monitored, eutrophic, seasonally stratified monomictic lake in the UK. The epilimnion shows a seasonal pattern of rising temperature and summer evaporative enrichment in 18O, and while there is a temperature imprint in both δ18Odiatom and δ18Ocalcite, there is significant inter-annual variability in both of these signals. The interpretation of δ18Odiatom and δ18Ocalcite values is complicated due to in-lake processes (e.g. non-equilibrium calcite precipitation, especially in spring, leading to significant 18Ocalcite depletion), and for δ18Odiatom, by post-mortem, depositional and possibly dissolution or diagenetic effects. For 2010 and 2011 respectively, there is a strong temperature dependence of δ18Ocalcite and δ18Odiatom in fresh trap material, with the fractionation slope for δ18Odiatom of ca. −0.2‰/°C, in agreement with several other studies. The δ18Odiatom data indicate the initiation of rapid post-mortem secondary alteration of fresh diatom silica (within ~6 months), with some trap material undergoing partial maturation in situ. Diatom δ18O of the trap material is also influenced by resuspension of diatom frustules from surface sediments (notably in summer 2011), with the net effect seen as an enrichment of deep-trap 18Odiatom by about +0.7‰ relative to shallow-trap values. Contact with anoxic water and anaerobic bacteria are potentially key to initiating this silica maturation process, as deep-trap samples that were removed prior to anoxia developing do not show enrichment. Dissolution (perhaps enhanced by anaerobic bacterial communities) may also be responsible for changes to δ18Odiatom that lead to increasing, but potentially predictable, error in inferred temperatures using this proxy. High resolution, multi-year monitoring can shed light on the complex dynamics affecting δ18Odiatom and δ18Ocalcite and supports the careful use of sedimentary δ18Odiatom and δ18Ocalcite as containing valuable hydroclimatic signals especially at a multi-annual resolution, although there remain substantial challenges to developing a reliable geothermometer on paired δ18Odiatom and δ18Ocalcite. In particular, δ18Odiatom needs cautious interpretation where silica post-mortem secondary alteration is incomplete and diatom preservation is not perfect, and we recommend dissolution be routinely assessed on diatom samples used for isotopic analyses.

中文翻译：

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了解当代温度信号通过碳酸盐和硅藻二氧化硅中的氧同位素配对比转移到湖泊沉积物中：问题和潜力

摘要 虽然方解石 (δ18Ocalcite) 的氧同位素组成 (δ18O) 和在较小程度上硅藻 (δ18Odiatom) 是过去水文气候（尤其是温度和地表水水文）的广泛使用的示踪剂，但这两种物质同时存在的程度在现代湖泊环境中获取它们的同位素信号，或者这些在初始沉积过程中是如何改变的，我们知之甚少。在这里，我们提供了一个来自天然湖沼学实验室的独特数据集来探索这些问题。本研究比较了 2 年（2010-12 年）内每两周一次的当代湖水样本的氧和氢同位素数据（δ18O、δ2H）与沉积物中的硅藻（δ18Odiatom）和方解石（δ18Ocalcite）的匹配集合位于 Rostherne Mere（最大深度 30 m）的陷阱（10 m 和 25 m），监控良好，英国的富营养化、季节性分层的单体湖。表层显示出 18O 温度升高和夏季蒸发富集的季节性模式，虽然 δ18O 硅藻和 δ18O 方解石都有温度印记，但这两种信号都存在显着的年际变化。由于湖内过程（例如非平衡方解石沉淀，特别是在春季，导致 18O 方解石显着耗竭），δ18Odiatom 和 δ18O方解石值的解释很复杂，而对于 δ18Odiatom，由于死后、沉积和可能的溶解或成岩作用. 分别在 2010 年和 2011 年，新鲜捕集材料中的 δ18O 方解石和 δ18O 硅藻具有很强的温度依赖性，δ18O 硅藻的分馏斜率约为 −0.2‰/°C，与其他几项研究一致。δ18Odiatom 数据表明新鲜硅藻二氧化硅在死后迅速发生二次改变（约 6 个月内），一些捕集材料在原位进行部分成熟。圈闭材料的硅藻 δ18O 还受到表层沉积物中硅藻壳再悬浮的影响（特别是在 2011 年夏季），净效应被视为深圈闭 18O 硅藻相对于浅圈圈值增加了约 +0.7‰。与缺氧水和厌氧细菌接触可能是启动此二氧化硅成熟过程的关键，因为在缺氧形成之前去除的深阱样品没有显示富集。溶解（可能由厌氧细菌群落增强）也可能导致 δ18Odiatom 的变化，导致增加，但可能是可预测的，使用此代理推断温度的错误。高分辨率、多年监测可以揭示影响 δ18O 硅藻和 δ18O 方解石的复杂动力学，并支持谨慎使用沉积 δ18O 硅藻和 δ18O 方解石，因为它们包含有价值的水文气候信号，尤其是在多年分辨率下，尽管开发可靠的水文气候仍然存在巨大挑战δ18Odiatom 和 δ18Ocalcite 上的地温计。特别是，δ18O 硅藻需要谨慎解释，其中二氧化硅死后二次蚀变不完整且硅藻保存不完美，我们建议对用于同位素分析的硅藻样品进行常规评估。多年监测可以揭示影响 δ18O 硅藻和 δ18O 方解石的复杂动力学，并支持谨慎使用沉积 δ18O 硅藻和 δ18O 方解石，因为它们包含有价值的水文气候信号，尤其是在多年分辨率下，尽管在配对上开发可靠的地温计仍然存在重大挑战δ18O硅藻和δ18O方解石。特别是，δ18O 硅藻需要谨慎解释，其中二氧化硅死后二次蚀变不完整且硅藻保存不完美，我们建议对用于同位素分析的硅藻样品进行常规评估。多年监测可以揭示影响 δ18O 硅藻和 δ18O 方解石的复杂动力学，并支持谨慎使用沉积 δ18O 硅藻和 δ18O 方解石，因为它们包含有价值的水文气候信号，尤其是在多年分辨率下，尽管在配对上开发可靠的地温计仍然存在重大挑战δ18O硅藻和δ18O方解石。特别是，δ18O 硅藻需要谨慎解释，其中二氧化硅死后二次蚀变不完整且硅藻保存不完美，我们建议对用于同位素分析的硅藻样品进行常规评估。尽管在配对的 δ18O 硅藻和 δ18O 方解石上开发可靠的地温计仍然存在巨大挑战。特别是，δ18O 硅藻需要谨慎解释，其中二氧化硅死后二次蚀变不完整且硅藻保存不完美，我们建议对用于同位素分析的硅藻样品进行常规评估。尽管在配对的 δ18O 硅藻和 δ18O 方解石上开发可靠的地温计仍然存在巨大挑战。特别是，δ18O 硅藻需要谨慎解释，其中二氧化硅死后二次蚀变不完整且硅藻保存不完美，我们建议对用于同位素分析的硅藻样品进行常规评估。