Lithium isotopes in speleothems: Temperature-controlled variation in silicate weathering during glacial cycles
Lithium isotopes in speleothems: Temperature-controlled variation in silicate weathering during glacial cycles
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DOI：
10.1016/j.epsl.2017.04.014
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发表时间：
2017-07
影响因子：
5.3
通讯作者：
P. V. Strandmann;A. Vaks;M. Bar-Matthews;A. Ayalon;E. Jacob;G. Henderson
中科院分区：
文献类型：
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作者：
P. V. Strandmann;A. Vaks;M. Bar-Matthews;A. Ayalon;E. Jacob;G. Henderson
硅酸盐矿物的陆地化学风化是碳和其他元素全球循环的基本组成部分。过去的温度、降雨量、冰盖、海平面和物理侵蚀的变化被认为会影响风化作用，但这些控制随时间的相对影响仍然很少受到限制。如果过去风化的性质可以被限制在个别地点，这个问题就可以得到解决。在这项研究中，我们研究了利用洞穴沉积物作为硅酸盐风化代理锂同位素的本地记录器。我们分析了过去 200 ka 期间在以色列两个洞穴（Soreq 和 Tzavoa）以及上覆土壤和岩石中形成的洞穴中的 δ 7 Li 和 [Li]。这些土壤和岩石的淋滤和质量平衡表明，锂主要来自上覆风积硅酸盐土壤的风化。 Speleothem δ 7 Li 值在冰川期 (∼ 23‰) 普遍高于间冰期 (∼ 10‰)，这意味着间冰期硅酸盐风化更加一致（其中“一致”是指原生矿物溶解与次生矿物形成的比例较高）。这些记录提供了有关以色列控制风化过程的信息。考虑导致这种风化一致性变化的可能过程表明温度的主要作用，较高的温度会导致更多的一致性风化（较低的 δ 7 Li speleo）。在这些地点观察到的洞穴化石 δ 7 Li 与气候之间的密切关系表明，Li 同位素可能是了解其他地点对风化作用的当地控制的强大工具，并且可用于评估伴随气候变化的风化变化的分布，例如更新世冰川循环的分布。
Terrestrial chemical weathering of silicate minerals is a fundamental component of the global cycle of carbon and other elements. Past changes in temperature, rainfall, ice cover, sea-level and physical erosion are thought to affect weathering but the relative impact of these controls through time remains poorly constrained. This problem could be addressed if the nature of past weathering could be constrained at individual sites. In this study, we investigate the use of speleothems as local recorders of the silicate weathering proxy, Li isotopes. We analysed δ 7 Li and [Li] in speleothems that formed during the past 200 ka in two well-studied Israeli caves (Soreq and Tzavoa), as well as in the overlying soils and rocks. Leaching and mass balance of these soils and rocks show that Li is dominantly sourced from weathering of the overlying aeolian silicate soils. Speleothem δ 7 Li values are ubiquitously higher during glacials (∼ 23‰) than during interglacials (∼ 10‰), implying more congruent silicate weathering during interglacials (where “congruent” means a high ratio of primary mineral dissolution to secondary mineral formation). These records provide information on the processes controlling weathering in Israel. Consideration of possible processes causing this change of weathering congruency indicates a primary role for temperature, with higher temperatures causing more congruent weathering (lower δ 7 Li speleo). The strong relationship observed between speleothem δ 7 Li and climate at these locations suggests that Li isotopes may be a powerful tool with which to understand the local controls on weathering at other sites, and could be used to assess the distribution of weathering changes accompanying climate change, such as that of Pleistocene glacial cycles.