Climate reconstruction from paired oxygen-isotope analyses of chironomid larval head capsules and endogenic carbonate (Hawes Water, UK) - Potential and problems
Climate reconstruction from paired oxygen-isotope analyses of chironomid larval head capsules and endogenic carbonate (Hawes Water, UK) - Potential and problems
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DOI：
10.1016/j.quascirev.2021.107160
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发表时间：
2021-09-02
影响因子：
4
通讯作者：
Thomas, Zoe
中科院分区：
文献类型：
--
作者：
Lombino, Alex;Atkinson, Tim;Thomas, Zoe
温度和大气水的氧同位素组成 (δ O-18) 都是重要的古气候变量，但分离它们对诸如碳酸盐湖的 δ O-18 等替代物的影响通常是有问题的。已知在晚冰期期间北部中纬度地区发生的巨大温度变化使得该区间成为将摇蚊幼虫头部胶囊的氧同位素分析与共生内源碳酸盐相结合的新方法的绝佳测试。我们将这种方法应用于来自霍斯沃特（英格兰西北部）的晚冰期湖泊沉积物序列。摇蚊头囊中的氧同位素值在晚冰期期间表现出明显的变化，与内源碳酸盐的氧同位素记录相似。然而，基于配对同位素值以及摇蚊和方解石之间的分馏的夏季温度重建产生-20至-4℃之间的值，这是不现实的，并且远远低于基于同一地点的摇蚊组合的重建。使用热解气相色谱质谱法测定的有限数量的摇蚊幼虫头部胶囊化石样本的成分表明存在脂肪族地质聚合物，这表明头部胶囊的成岩作用系统地偏差了同位素衍生的温度估计。然而，两个来源的同位素记录的类似趋势表明古气候信号仍然保留下来。 (C) 2021 作者。由爱思唯尔有限公司出版
Temperature and the oxygen isotopic composition (delta O-18) of meteoric water are both important palaeoclimatic variables, but separating their influences on proxies such as the delta O-18 of lake carbonates is often problematic. The large temperature variations that are known to have occurred in the northern mid-latitudes during the Late Glacial make this interval an excellent test for a novel approach that combines oxygen-isotope analyses of chironomid larval head capsules with co-occurring endogenic carbonate. We apply this approach to a Late Glacial lake sediment sequence from Hawes Water (NW England). Oxygen-isotope values in chironomid head capsules show marked variations during the Late Glacial that are similar to the oxygen isotope record from endogenic carbonate. However, summer temperature reconstructions based on the paired isotope values and fractionation between chironomids and calcite yield values between -20 and -4 degrees C, which are unrealistic and far lower than reconstructions based on chironomid assemblages at the same site. The composition of a limited number of samples of fossil chironomid larval head capsules determined using Pyrolysis gas-chromatography mass spectrometry indicates the presence of aliphatic geopolymers, suggesting that diagenetic alteration of the head capsules has systematically biased the isotope-derived temperature estimates. However, a similar trend in the isotope records of the two sources suggests that a palaeoclimate signal is still preserved. (C) 2021 The Authors. Published by Elsevier Ltd.