Modelling fractionation of stable isotopes in stalagmites
Modelling fractionation of stable isotopes in stalagmites
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DOI：
10.1016/j.gca.2009.09.010
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发表时间：
2009-12-15
影响因子：
5
通讯作者：
Mangini, Augusto
中科院分区：
文献类型：
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作者：
Muehlinghuas, Christian;Scholz, Denis;Mangini, Augusto
高分辨率三角洲C-13和三角洲O-18剖面记录在精确定年的洞穴沉积物中，是广泛使用的过去气候的代用指标。δ C-13和δ O-18都依赖于几种与气候有关的效应，包括气象过程、洞穴上方土壤区发生的过程和石笋表面溶液层发生的同位素分馏过程。在这里，我们使用石笋同位素和生长模型模拟后者，并确定洞穴方解石中稳定同位素值与洞穴参数（如温度，滴水间隔，水p（CO2）和描述溶液层和撞击液滴之间混合过程的混合系数。13的值被建模为瑞利蒸馏过程，并显示出显着的依赖于在石笋表面上的溶液的停留时间和滴液间隔，分别。相比之下，δ O-18值的演变也受到溶液中的碳酸氢盐和滴水之间的缓冲反应的影响，该缓冲反应将碳酸氢盐的δ O-18值推向滴水和方解石之间平衡同位素分馏的预期值。这减弱了Δ O-18值对滴注间隔的依赖性。然而，δ O-18的温度依赖性比δ C-13更明显，并且在与平衡条件下分馏所预期的类似范围内，我们还研究了δ C-13和δ O-18值沿沿着单个生长层的同位素富集，因此，预期的斜率为亨迪测试。结果表明，只有在不平衡条件下发生同位素分馏时，才有可能进行正亨迪检验。然而，阴性亨迪检验并不排除同位素分馏发生在不平衡条件下。不平衡分馏的更可靠指标是δ C-13值沿单个生长层沿着富集。(C)2009爱思唯尔有限公司保留所有权利。
High resolution delta C-13 and delta O-18 profiles recorded in precisely dated spelcothems are widely used proxies for the climate of the past. Both delta C-13 and delta O-18 depend oil several climate related effects including meteorological processes, processes occurring in the soil zone above the cave and isotope fractionation processes occurring in the Solution layer on the stalagmite surface. Here we model the latter using a stalagmite isotope and growth model and determine the relationship between the stable isotope Values in speleothem calcite and cave parameters, such as temperature, drip interval, water p(CO2) and a mixing coefficient describing mixing processes between the solution layer and the impinging drop.The evolution of delta C-13 values is modelled as a Rayleigh distillation process and shows a pronounced dependence on the residence time of the solution on the stalagmite surface and the drip interval, respectively. The evolution of delta O-18 values, in contrast, is also influenced by buffering reactions between the bicarbonate in the solution and the drip water driving the delta O-18 value of the bicarbonate towards the value expected for equilibrium isotope fractionation between drip water and calcite. This attenuates the dependence of the delta O-18 values on drip interval. The temperature dependence of delta O-18, however, is more pronounced than for delta C-13 and in a similar range as expected for fractionation under equilibrium conditions.We also investigate the isotopic enrichment of the delta C-13 and delta O-18 values along individual growth layers and, thus, the slopes expected for Hendy tests. The results show that a positive Hendy test is only possible if isotope fractionation occurred under disequilibrium conditions. However, a negative Hendy test does not exclude that isotope fractionation occurred under disequilibrium conditions. A more reliable indicator for disequilibrium fractionation is the enrichment of the delta C-13 values along an individual growth layer. (C) 2009 Elsevier Ltd. All rights reserved.