Modelling the δ18O value of cave drip water and speleothem calcite
Modelling the δ18O value of cave drip water and speleothem calcite
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DOI：
10.1016/j.epsl.2010.09.019
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发表时间：
2010-11
影响因子：
5.3
通讯作者：
A. Wackerbarth;D. Scholz;J. Fohlmeister;A. Mangini
中科院分区：
文献类型：
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作者：
A. Wackerbarth;D. Scholz;J. Fohlmeister;A. Mangini
近年来，在洞穴中记录的稳定同位素信号为了解过去的气候变化提供了重要的见解。然而，由于稳定同位素信号受到各种过程的影响，对年平均温度和降水量的定量重建仍然很困难。本文建立了一个滴落水模型，揭示了这些气候参数对洞穴滴落水氧同位素信号的影响。在模型中，通过与冬季降水量和冬季气温的相关性，建立了降水δ18O值与年平均气温的相关性。将该模型应用于德国西部的两个洞穴，揭示了冬季降雨对该地区洞穴滴水氧同位素组成的强烈影响。假设滴水和方解石之间的同位素分馏平衡，我们提供了一个有关洞穴方解石δ18O值与年平均地表温度的函数。该函数表明温度与溶洞方解石的δ18O值之间存在明显的反相关关系，这在中欧和北欧的几个溶洞中已有报道。通过对该函数的逆应用，我们从德国西部阿塔和邦克洞两个石笋的δ18O信号中初步重建了6 ~ 1.5ka的平均温度。所得的温度曲线对冬季降水量与冬季温度的相关性值非常敏感。由于这种相关性在过去可能不是恒定的，因此重建的温度曲线具有很大的不确定性。
Stable isotope signals recorded in speleothems have provided important insights about past climate variability in recent years. Quantitative reconstruction of mean annual temperature and the amount of precipitation, however, remains difficult because the stable isotope signals are influenced by various processes. Here we present a drip water model, which shows how these climate parameters affect the oxygen isotope signal of cave drip water. In the model the dependence of the δ18O value of drip water on mean annual temperature is established by correlation to the amount of winter precipitation and winter temperature. Application of the model to two caves in western Germany reveals a strong influence of winter rainfall on the oxygen isotope composition of cave drip water in this region. Assuming equilibrium isotope fractionation between drip water and calcite, we provide a function relating the δ18O value of speleothem calcite to mean annual surface temperature. This function shows a clear anticorrelation between temperature and the δ18O value of speleothem calcite, which has been previously reported for several caves in central and northern Europe. By inverse application of this function, we tentatively reconstruct average temperatures for the period between 6 and 1.5ka from the δ18O signals of two stalagmites from Atta and Bunker Cave (western Germany). The resulting temperature curves are very sensitive to the value used for the correlation between the amount of winter precipitation and winter temperature. Since this correlation was probably not constant in the past, the reconstructed temperature curves are associated with substantial uncertainty.