Temperature and the oxygen isotopic composition (δ¹⁸O) of meteoric water are both important palaeoclimatic variables, but separating their influences on proxies such as the δ¹⁸O 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 °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.

大气水的温度和氧同位素组成 (δ ¹⁸ O) 都是重要的古气候变量，但将它们对诸如 δ ¹⁸等代理变量的影响分开湖碳酸盐中的 O 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该间隔成为对一种将摇蚊幼虫头部胶囊的氧同位素分析与共生的内生碳酸盐相结合的新方法的极好测试。我们将此方法应用于来自 Hawes Water（英格兰西北部）的晚冰川湖沉积物序列。摇蚊头部胶囊中的氧同位素值在晚冰期期间显示出明显的变化，类似于内源碳酸盐的氧同位素记录。然而，基于配对同位素值和摇蚊和方解石屈服值之间的分馏的夏季温度重建在 -20 和 -4 °C 之间，这是不现实的，远低于基于同一地点摇蚊组合的重建。使用热解气相色谱质谱法确定的数量有限的化石摇蚊幼虫头部胶囊样品的组成表明存在脂肪族地质聚合物，这表明头部胶囊的成岩改变系统地使同位素衍生的温度估计值存在偏差。然而，两个来源的同位素记录中的相似趋势表明古气候信号仍然保留。表明头部胶囊的成岩作用已经系统地偏向了同位素衍生的温度估计。然而，两个来源的同位素记录中的相似趋势表明古气候信号仍然保留。表明头部胶囊的成岩作用已经系统地偏向了同位素衍生的温度估计。然而，两个来源的同位素记录中的相似趋势表明古气候信号仍然保留。