Understanding the transfer of contemporary temperature signals into lake sediments via paired oxygen isotope ratios in carbonates and diatom silica: Problems and potential
Understanding the transfer of contemporary temperature signals into lake sediments via paired oxygen isotope ratios in carbonates and diatom silica: Problems and potential
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了解通过碳酸盐和硅藻二氧化硅中成对的氧同位素比率将当代温度信号转移到湖泊沉积物中：问题和潜力
DOI：
10.1016/j.chemgeo.2020.119705
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发表时间：
2020
期刊：
影响因子：
3.9
通讯作者：
Ryves D
中科院分区：
文献类型：
--
作者：
Ryves D
虽然方解石(δ18O)的氧同位素组成(δ18O)和硅藻二氧化硅(δ18O)在较小程度上是过去水文气候(特别是温度和地表水水文)的示踪剂，但这两个宿主在现代湖泊环境中同时获得同位素信号的程度，或者这些信号在初始沉积过程中是如何变化的，人们了解得很少。在这里，我们提出了一个独特的数据集，从一个自然湖泊实验室来探索这些问题。这项研究比较了两年期间(2010年至2012年)每两周一次的当代湖水样本的氧和氢同位素数据(δ18O，δ2H)，以及来自罗斯梅尔(最大深度30米)沉积物陷阱(10米和25米)的硅藻(δ180硅藻)和方解石(δ180方解石)的配对收集。罗斯梅尔是一个监测良好的、富营养化的、季节性分层的单体湖泊。18O的温度升高和夏季蒸发富集具有季节特征，虽然δ18O硅藻土和δ18O方解石中都有温度印记，但这两个信号都存在显著的年际变化。由于湖内过程(例如方解石的非平衡沉淀，特别是在春季，导致180O的钙质耗竭)，以及对δ180型硅藻的身体、沉积以及可能的溶解或成岩作用的影响，对δ180型硅藻和δ180型硅藻的解释复杂。2010年和2011年，新鲜捕集材料中δ180和δ180硅藻的温度依赖性很强，δ180硅藻的分馏斜率约为−0.2‰/°C，这与其他几项研究一致。δ~(18)硅藻数据表明，新鲜硅藻硅质在死后(~6个月内)开始快速二次蚀变，部分圈闭物质在原地经历了部分成熟。圈闭材料中的硅藻δ18O还受到表层沉积物中硅藻树枝的再悬浮的影响(2011年夏季尤为明显)，净影响被视为深层圈闭18O的富集量比浅层圈闭的值高出约0.7‰。与缺氧水和厌氧细菌的接触可能是启动这一二氧化硅成熟过程的关键，因为在缺氧形成之前移除的深陷阱样品没有显示出浓缩。溶解(可能受到厌氧细菌群落的促进)也可能是δ180硅藻变化的原因，这些变化导致使用该试剂推断温度的误差增加，但可能是可预测的。高分辨率的多年监测可以揭示影响δ180硅藻和δ180解石的复杂动力学，并支持谨慎使用包含有价值的水文气候信号的沉积δ180硅藻和δ180解石，特别是在多年分辨率下，尽管在成对的δ180硅藻和δ180方解石上开发可靠的地质温度计仍然存在巨大挑战。特别是，在硅质死后次生蚀变不完整和硅藻保存不完善的情况下，需要谨慎解释δ180硅藻，我们建议对用于同位素分析的硅藻样品进行常规的溶解评估。
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 in18O, and while there is a temperature imprint in both δ18Odiatomand δ18Ocalcite, there is significant inter-annual variability in both of these signals. The interpretation of δ18Odiatomand δ18Ocalcitevalues is complicated due to in-lake processes (e.g. non-equilibrium calcite precipitation, especially in spring, leading to significant18Ocalcitedepletion), 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 δ18Ocalciteand δ18Odiatomin fresh trap material, with the fractionation slope for δ18Odiatomof ca. −0.2‰/°C, in agreement with several other studies. The δ18Odiatomdata 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-trap18Odiatomby 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 δ18Odiatomthat 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 δ18Odiatomand δ18Ocalciteand supports the careful use of sedimentary δ18Odiatomand δ18Ocalciteas containing valuable hydroclimatic signals especially at a multi-annual resolution, although there remain substantial challenges to developing a reliable geothermometer on paired δ18Odiatomand δ18Ocalcite. In particular, δ18Odiatomneeds 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.
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发表时间：
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