A reactive transport approach to modeling cave seepage water chemistry II: Elemental signatures
A reactive transport approach to modeling cave seepage water chemistry II: Elemental signatures
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DOI：
10.1016/j.gca.2021.06.040
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发表时间：
2021-07
影响因子：
5
通讯作者：
J. Oster;A. Covey;C. Lawrence;M. Giannetta;J. Druhan
中科院分区：
文献类型：
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作者：
J. Oster;A. Covey;C. Lawrence;M. Giannetta;J. Druhan
岩溶系统是有用的检查空间和时间的变化，在关键区的过程，因为他们提供了一个窗口，地下沃茨与植被，土壤，风化层，基岩在一系列的长度和时间尺度的相互作用。这些水文路径通常包括洞穴沉积物的沉淀，提供了气候和环境变化的长期档案。洞穴沉积物中的微量元素比值（Mg/Ca，Sr/Ca，Ba/Ca）有可能提供有关降雨和渗透的过去变化的信息，但对它们的控制可能是复杂的，它们的解释必须基于对现代洞穴系统的理解。在这里，我们整合的表面条件，基岩，土壤和滴水化学的蓝泉洞在美国田纳西州的反应传输模型CrunchTope，我们已经校准的岩溶系统，调查洞穴渗漏沃茨中的微量元素变化的主要控制观察。我们发现，测得的滴水Mg/Ca和Sr/Ca被捕获的模型内，通过变量的石灰岩溶解，其次是沉淀的次生方解石发生在洞穴内，而不是主机石灰岩。然而，强有力的空间控制滴水镁/钙和锶/钙可能反映渗流水相互作用与变量的成岩阶段的寄主岩石。与此相反，Ba/Ca值是一致的整个洞穴，并与有效降雨量而变化，这表明该参数可能是最一致的石灰石溶解和方解石沉淀之前的度量，可以作为一个代理降雨和渗透在这个洞穴系统。我们的研究结果强调了洞穴滴水沃茨的空间异质性评估的重要性，并概述了一种新的建模方法，用于确定滴水化学的主导控制，以支持古气候记录的解释。
Karst systems are useful for examining spatial and temporal variability in Critical Zone processes because they provide a window into the subsurface where waters have interacted with vegetation, soils, regolith, and bedrock across a range of length and timescales. These hydrologic pathways frequently include the precipitation of speleothems, which provide long-term archives of climate and environmental change. Trace element ratios in speleothems (Mg/Ca, Sr/Ca, Ba/Ca) have the potential to provide information about past changes in rainfall and infiltration, but controls on them can be complex and their interpretation must be based on an understanding of the modern cave system. Here we integrate observations of surface conditions, bedrock, soil, and drip water chemistry of Blue Spring Cave in Tennessee, USA with the reactive transport model CrunchTope, which we have calibrated for karst systems to investigate the primary controls on trace element variations in cave seepage waters. We find that measured drip water Mg/Ca and Sr/Ca are captured within the model through variable amounts of limestone dissolution followed by precipitation of secondary calcite that happens within the cave rather than the host limestone. However, strong spatial controls on drip water Mg/Ca and Sr/Ca likely reflect seepage water interactions with variable amounts of diagenetic phases in the host rock. In contrast, Ba/Ca values are consistent across the cave and vary with effective rainfall, suggesting that this parameter may be the most consistent metric for limestone dissolution and prior calcite precipitation and can act as a proxy for rainfall and infiltration in this cave system. Our findings emphasize the importance of evaluating spatial heterogeneity in cave drip waters and outline a novel modeling approach for determining the dominant controls on drip water chemistry in support of the interpretations of paleoclimate records.