Model results of orbital forcing and solar activity during the Holocene in NetCDF format@en

In this study we investigate the impact of mid- and late Holocene orbital forcing and solar activity on variations of the oxygen isotopic composition in precipitation. The investigation is motivated by a recently published speleothem d18O record from the well-monitored Bunker Cave in Germany. The record reveals some high variability on multi-centennial to millennial scales that does not linearly correspond to orbital forcing. Our model study is based on a set of novel climate simulations performed with the atmosphere general circulation model ECHAM5-wiso enhanced by explicit water isotope diagnostics. From the performed model experiments, we derive the following major results: (1) the response of both orbital and solar forcing lead to changes in surface temperatures and d18O in precipitation with similar magnitudes during the mid- and late Holocene. (2) Past d18O anomalies correspond to changing temperatures in the orbital driven simulations. This does not hold true if an additional solar forcing is added. (3) Two orbital driven mid-Holocene experiments, simulating the mean climate state approximately 5000 and 6000 yr ago, yield very similar results. However, if an identical additional solar activity-induced forcing is added, the simulated changes of surface temperatures as well as d18O between both periods differ. We conclude from our simulation results that non-linear effects and feedbacks of the orbital and solar activity forcing substantially alter the d18O in precipitation pattern and its relation to temperature change.

本研究探讨了全新世（Holocene）中晚期轨道强迫（orbital forcing）与太阳活动（solar activity）对降水中氧同位素组成（oxygen isotopic composition）变化的影响。本研究的动机源自德国经全面监测的邦克洞穴（Bunker Cave）中最新发表的石笋（speleothem）d¹⁸O记录，该记录显示出百年至千年尺度上的显著波动，且其变化与轨道强迫并非线性相关。本研究的模拟实验基于一套全新的气候模拟方案，采用引入了显式水同位素诊断（water isotope diagnostics）模块的大气环流模式（Atmosphere General Circulation Model）ECHAM5-wiso完成。通过上述模型实验，我们得到以下核心结论：（1）在全新世中晚期，轨道强迫与太阳强迫对地表温度及降水中d¹⁸O的影响幅度相当；（2）在仅受轨道强迫的模拟实验中，过往的d¹⁸O异常与温度变化存在对应关系，但若额外叠加太阳强迫，则该对应关系不再成立；（3）两项仅受轨道强迫的全新世中期模拟实验——分别模拟约5000年和6000年前的平均气候状态——得到了高度相似的结果，但若为两项实验均施加相同的太阳活动诱导强迫，则两个模拟时段的地表温度与降水中d¹⁸O的变化均出现差异。基于上述模拟结果，我们得出结论：轨道强迫与太阳活动强迫的非线性效应及反馈过程，会显著改变降水中d¹⁸O的分布格局及其与温度变化的关联。