Lake Dynamics Modulate the Air Temperature Variability Recorded by Sedimentary Aquatic Biomarkers: A Holocene Case Study From Western Greenland
Lake Dynamics Modulate the Air Temperature Variability Recorded by Sedimentary Aquatic Biomarkers: A Holocene Case Study From Western Greenland
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DOI：
10.1029/2022jg007106
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发表时间：
2023-06
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影响因子：
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通讯作者：
A. Cluett;E. Thomas;N. McKay;O. Cowling;I. Castañeda;C. Morrill
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作者：
A. Cluett;E. Thomas;N. McKay;O. Cowling;I. Castañeda;C. Morrill
定量温度重建湖泊有机地球化学代理，包括支链甘油二烷基甘油四醚（brGDGT）和烯酮提供了关键的制约过去的大陆气候。然而，从代理的气温估计可能会受到季节性空气和水温之间关系的非平稳性的影响，这是一个尚未在强季节性高纬度环境中研究的因素。我们对brGDGT和烯酮通过全新世在相同样品上测量的底层分析与基于格陵兰西部湖泊热力学湖泊模型模拟的前向建模代理值进行了配对。测量的brGDGT分布表明，稳定的本地（水生）生产压倒了外来输入的大多数样本，证明使用湖泊模型来解释温度驱动的变化。烯酮的传统校准（仅在5500年BP后检测到）表明比brGDGT的传统校准大得多的温度变化。代理测量值与正演模拟值的比较表明，brGDGT分布的变化单调地反映了多年夏季气温的变化，尽管无冰季节的长度减弱了气温对水温的影响。烯酮变化的驱动因素仍然不太清楚;潜在的影响包括代理生产的季节性变化或对特定年份的偏差，这两个因素都是相关季节窗口期间水-空气温度敏感性的非线性。我们证明，由于在代理合成窗口期间空气-水温度敏感性的差异，隐含的温度变化在代理之间可能存在很大差异，而不需要在湖泊或当地气候中进行阈值行为，并建议未来的研究将湖泊建模纳入约束这种不确定性。
Quantitative temperature reconstructions from lacustrine organic geochemical proxies including branched glycerol dialkyl glycerol tetraethers (brGDGTs) and alkenones provide key constraints on past continental climates. However, estimation of air temperatures from proxies can be impacted by non‐stationarity in the relationships between seasonal air and water temperatures, a factor not yet examined in strongly seasonal high‐latitude settings. We pair downcore analyses of brGDGTs and alkenones measured on the same samples through the Holocene with forward‐modeled proxy values based on thermodynamic lake model simulations for a western Greenland lake. The measured brGDGT distributions suggest that stable autochthonous (aquatic) production overpowers allochthonous inputs for most samples, justifying the use of the lake model to interpret temperature‐driven changes. Conventional calibration of alkenones (detected only after 5.5 thousand years BP) suggests substantially larger temperature variations than conventional calibration of brGDGTs. Comparison of proxy measurements to forward‐modeled values suggests variations in brGDGT distributions monotonically reflect multi‐decadal summer air temperatures changes, although the length of the ice‐free season dampens the influence of air temperatures on water temperatures. Drivers of alkenone variability remain less clear; potential influences include small changes in the seasonality of proxy production or biases toward specific years, both underlain by non‐linearity in water‐air temperature sensitivity during relevant seasonal windows. We demonstrate that implied temperature variability can differ substantially between proxies because of differences in air‐water temperature sensitivity during windows of proxy synthesis without necessitating threshold behavior in the lake or local climate, and recommend that future studies incorporate lake modeling to constrain this uncertainty.