Improving the understanding of changes in the mean and variability of climate variables as well as their interrelation is crucial for reliable climate change projections. Comparisons between general circulation models and paleoclimate archives using indirect proxies for temperature or precipitation have been used to test and validate the capability of climate models to represent climate changes. The oxygen isotopic ratio δ¹⁸O, a proxy for many different climate variables, is routinely measured in speleothem samples at decadal or higher resolution, and single specimens can cover full glacial–interglacial cycles. The calcium carbonate cave deposits are precisely dateable and provide well preserved (semi-)continuous albeit multivariate climate signals in the lower and mid-latitudes, where the measured δ¹⁸O in the mineral does not directly represent temperature or precipitation. Therefore, speleothems represent suitable archives to assess climate model abilities to simulate climate variability beyond the timescales covered by meteorological observations (10¹–10² years).Here, we present three transient isotope-enabled simulations from the Hadley Center Climate Model version 3 (iHadCM3) covering the last millennium (850–1850 CE) and compare them to a large global dataset of speleothem δ¹⁸O records from the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database version 2 (Comas-Bru et al., 2020b). We systematically evaluate offsets in mean and variance of simulated δ¹⁸O and test for the main climate drivers recorded in δ¹⁸O for individual records or regions.The time-mean spatial offsets between the simulated δ¹⁸O and the speleothem data are fairly small. However, using robust filters and spectral analysis, we show that the observed archive-based variability of δ¹⁸O is lower than simulated by iHadCM3 on decadal and higher on centennial timescales. Most of this difference can likely be attributed to the records' lower temporal resolution and averaging or smoothing processes affecting the δ¹⁸O signal, e.g., through soil water residence times. Using cross-correlation analyses at site level and modeled grid-box level, we find evidence for highly variable but generally low signal-to-noise ratios in the proxy data. This points to a high influence of cave-internal processes and regional climate particularities and could suggest low regional representativity of individual sites. Long-range strong positive correlations dominate the speleothem correlation network but are much weaker in the simulation. One reason for this could lie in a lack of long-term internal climate variability in these model simulations, which could be tested by repeating similar comparisons with other isotope-enabled climate models and paleoclimate databases.

中文翻译：

---

脾科记录和最近一个世纪的iHadCM3模型模拟中氧同位素特征的比较

加强对气候变量均值和变异性及其相互关系的认识，对于可靠的气候变化预测至关重要。使用温度或降水的间接代理进行的一般循环模型与古气候档案之间的比较已用于测试和验证气候模型代表气候变化的能力。氧同位素比率δ ¹⁸ ösaleothem样品通常以十年或更高的分辨率进行测量，它是许多不同气候变量的代名词，单个样品可以覆盖整个冰川-冰川间的周期。碳酸钙洞穴沉积物是精确dateable并提供保存完好（半）连续尽管在下和纬度，其中测量的多元气候信号δ ¹⁸ ö在矿物并不直接代表温度或沉淀。因此，speleothems代表了合适的档案库，用于评估气候模型模拟气象观测所涵盖的时间范围以外的气候变异性的能力（10 ¹ – 10 ² 年）。在这里，从哈德利中心气候模式版本3（iHadCM3）覆盖近千年（850-1850 CE），我们目前三种瞬态启用同位素模拟和把它们比作一个大的全球数据集的钟乳石δ ^18个Ø从记录Speleothem同位素合成与分析（SISAL）数据库版本2 （Comas-Bru等人，2020b）。我们系统评估的模拟在均值和方差的偏移δ ¹⁸ Ø和测试记录在主驱动气候δ ¹⁸ Ø对于模拟之间的个人记录或regions.The时间平均空间偏移δ ¹⁸ Ø而且脾脏数据非常小。然而，使用鲁棒过滤器和频谱分析，我们表明，所观察到的基于档案变异性δ ¹⁸ ö低于上十年模拟由iHadCM3和更高的上百年的时间尺度。大多数这种差异可能可以归因于记录降低时间分辨率和平均或平滑处理影响δ ¹⁸ Ø信号，例如通过土壤水停留时间。使用站点级别和建模的网格框级别的互相关分析，我们发现在代理数据中存在高度可变但信噪比通常较低的证据。这表明了洞穴内部过程和区域气候特殊性的巨大影响，并可能表明单个地点的区域代表性较低。远距离强正相关性支配着脾动脉相关性网络，但在仿真中却弱得多。原因之一可能是这些模型模拟中缺乏长期的内部气候变异性，可以通过与其他具有同位素功能的气候模型和古气候数据库重复类似的比较来进行测试。