Simulated oxygen isotopes in cave drip water and speleothem calcite in European caves
Simulated oxygen isotopes in cave drip water and speleothem calcite in European caves
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DOI：
10.5194/cp-8-1781-2012
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发表时间：
2012-11
影响因子：
4.3
通讯作者：
A. Wackerbarth;P. Langebroek;M. Werner;Gerrit Lohmann;S. Riechelmann;A. Borsato;A. Mangini
中科院分区：
文献类型：
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作者：
A. Wackerbarth;P. Langebroek;M. Werner;Gerrit Lohmann;S. Riechelmann;A. Borsato;A. Mangini
石笋稳定氧同位素（δ 18o）记录的解译仍然是石笋研究的复杂任务之一。在这里，我们提出了一种新的基于模型的方法，我们将一个描述从雨水到洞穴方解石的δ 18o过程和变化的模型（氧同位素滴水和石笋模型- ODSM）与最先进的大气环流模型的结果相结合，该模型得到了显式同位素诊断（ECHAM5-wiso）的增强。该方法既不针对气候，也不针对洞穴，可以综合评估不同气候变量（如温度和降水量）对滴水和洞穴方解石同位素组成的影响。首先，我们利用来自欧洲不同地理区域的七个洞穴的观测数据，在当今气候条件下应用和评估了这种新方法。每个洞穴都提供了滴水和洞穴方解石的δ 18o测量值，我们将其与模拟同位素值进行比较。在7个溶洞中，有6个溶洞中滴水和溶洞方解石的δ 18o模拟值与观测值吻合较好。其余洞穴的不匹配可能是由于洞穴系统的复杂性造成的，超出了我们的洞穴模型所包含的参数化。然后，我们利用ECHAM5-wiso的6 ka模拟结果，通过强迫ODSM来研究洞穴系统对全新世中期（距今6000年，6 ka）气候条件的响应。对于一组12个欧洲洞穴，我们比较了模拟的中全新世与现代洞穴中方解石δ 18o的差异与现有测量值。我们表明，欧洲的总体变化被很好地模拟了。然而，发现了局部差异，这可能是由于模型分辨率太低，影响蒸散发的复杂的局部土壤-大气相互作用或洞穴特定因素（如非平衡分馏过程）造成的。中全新世实验表明，该方法具有在大空间（区域到全球）尺度上分析δ 18o变化的潜力。模拟和实测的欧洲石笋样品的δ 18o值表明，在此之前6 ka，北大西洋涛动存在强烈的正模态，这得到了各自模拟气候参数的支持。
Interpreting stable oxygen isotope (δ 18 O) records from stalagmites is still one of the complex tasks in speleothem research. Here, we present a novel model-based approach, where we force a model describing the processes and modifications of δ 18 O from rain water to speleothem calcite (Oxygen isotope Drip water and Stalagmite Model – ODSM) with the results of a state-of-the-art atmospheric general circulation model enhanced by explicit isotope diagnostics (ECHAM5-wiso). The approach is neither climate nor cave-specific and allows an integrated assessment of the influence of different varying climate variables, e.g. temperature and precipitation amount, on the isotopic composition of drip water and speleothem calcite. First, we apply and evaluate this new approach under present-day climate conditions using observational data from seven caves from different geographical regions in Europe. Each of these caves provides measured δ 18 O values of drip water and speleothem calcite to which we compare our simulated isotope values. For six of the seven caves modeled δ 18 O values of drip water and speleothem calcite are in good agreement with observed values. The mismatch of the remaining caves might be caused by the complexity of the cave system, beyond the parameterizations included in our cave model. We then examine the response of the cave system to mid-Holocene (6000 yr before present, 6 ka) climate conditions by forcing the ODSM with ECHAM5-wiso results from 6 ka simulations. For a set of twelve European caves, we compare the modeled mid-Holocene-to-modern difference in speleothem calcite δ 18 O to available measurements. We show that the general European changes are simulated well. However, local discrepancies are found, and might be explained either by a too low model resolution, complex local soil-atmosphere interactions affecting evapotranspiration or by cave specific factors such as non-equilibrium fractionation processes. The mid-Holocene experiment pronounces the potential of the presented approach to analyse δ 18 O variations on a spatially large (regional to global) scale. Modelled as well as measured European δ 18 O values of stalagmite samples suggest the presence of a strong, positive mode of the North Atlantic Oscillation at 6 ka before present, which is supported by the respective modelled climate parameters.