Modern stalagmite δ18O: Instrumental calibration and forward modelling
Modern stalagmite δ18O: Instrumental calibration and forward modelling
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DOI：
10.1016/j.gloplacha.2009.05.002
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发表时间：
2010-04
影响因子：
3.9
通讯作者：
A. Baker;C. Bradley
中科院分区：
文献类型：
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作者：
A. Baker;C. Bradley
石笋方解石的δ18O同位素组成通常包含气候信号，但难以用降雨或温度来解释。在冰期-间冰期和年代际采样分辨率上，石笋δ18O明显包含一个“一级”气候信号，其中温度和海洋/大气环流的变化幅度主导了δ18O信号。然而，在年-两年分辨率采样和间冰期，气候变化幅度较小，土壤、岩溶地下水和洞穴过程引入的δ18O变率可能给石笋δ18O记录的气候解释带来相当大的不确定性。本文讨论了两种量化石笋δ18O所含气候信号的方法。首先，综述了基于线性回归的石笋δ18O与仪器气候参数（如温度和降雨量）的关联方法。讨论了试图解释岩溶含水层内地下水混合的复杂线性回归方法的优缺点。其次，介绍了一种正演模拟方法，其中石笋δ18O由降雨δ18O、地表气候参数和简单的喀斯特水文模型模拟。以直布罗陀为例，后一种方法表明，1‰量级的石笋δ18O变化完全可以用喀斯特水文差异来解释。正演模拟表明，在洞穴内的石笋之间，或在均匀气候区内的洞穴之间，可能观察到类似的δ18O变化，并强调了试图使用δ18O作为古温度计的困难。
The δ18O isotopic composition of stalagmite calcite frequently contains a climate signal, but one that is difficult to interpret in terms of either rainfall or temperature. Over glacial–interglacial time periods and decadal sampling resolution, stalagmite δ18O clearly contains a ‘first order’ climate signal where the magnitude of changes in temperature and ocean/atmospheric circulation dominate the δ18O signature. However, at annual–biennial resolution sampling, and within interglacial periods, the magnitude of climate changes is smaller, and variability in δ18O introduced by soil, karst groundwater and cave processes can introduce considerable uncertainty into the climatic interpretation of stalagmite δ18O records. Here, two approaches that can quantify the climate signal contained with stalagmite δ18O are discussed. Firstly, linear regression based approaches are reviewed, which correlate stalagmite δ18O with instrumental climate parameters such as temperature and rainfall. The advantages and disadvantages of complex linear regression approaches that attempt to account for groundwater mixing within the karst aquifer are discussed. Secondly, a forward modelling approach is introduced, where stalagmite δ18O is modelled from rainfall δ18O, surface climate parameters and a simple karst hydrology model. Using a case study from Gibraltar, this latter approach demonstrates that between stalagmite variability in δ18O of the order of 1‰ can be explained solely by differences in karst hydrology. Forward modelling suggests that a similar variability in δ18O might be observed between stalagmites within a cave, or between caves within a homogenous climate region, and highlights the difficulty in attempting to use δ18O as a paleo-thermometer.