Calcium isotopes tracing secondary mineral formation in the high-relief Yalong River Basin, Southeast Tibetan Plateau.
Calcium isotopes tracing secondary mineral formation in the high-relief Yalong River Basin, Southeast Tibetan Plateau.
复制标题
钙同位素追踪青藏高原东南部高地貌雅砻江盆地次生矿物形成。
DOI：
10.1016/j.scitotenv.2022.154315
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Chen BB
中科院分区：
文献类型：
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作者：
Chen BB
钙是全球碳循环中的关键元素，因为它在通过硅酸盐风化和碳酸盐形成的碳封存中起作用。在这里，我们应用钙（δ44/40 Ca）和锶（87 Sr/86 Sr）同位素来探索这样的化学风化过程中的河流系统排水的各种地质和气候环境：雅砻江，中国，及其支流。这条河发源于青藏高原，是中国长江的上游之一。雅砻江溶解负荷的Ca同位素组成范围为0.60‰ ~ 1.02‰（相对于NIST标准SRM 915 a）。高原和低地河流的δ44/40 Ca值较高，山区河流的δ44/40 Ca值较低。河流溶解的δ44/40 Ca值、Sr/Ca比值和方解石饱和度指数之间的相关性表明，次生碳酸盐的沉淀控制了该河流系统大部分地区的Ca同位素组成和碳转化。然而，这种相关性在低地支流中并不存在，在那里，δ44/40 Ca和锂（Li）同位素之间的关系反而表明了地形和气候的控制，通过次生粘土矿物的形成。具体而言，低地地区的大雨降低了土壤溶液的pH值，从而抑制了次生碳酸盐的沉淀。此外，平坦的地形和厚的土壤增加了水-岩相互作用的时间，这有利于形成次生粘土矿物，优先纳入较轻的Ca同位素。总的来说，这项研究突出了稳定的钙同位素的潜力，当与其他同位素系统（如锶和锂同位素）结合使用时，量化在大型河流流域的次生矿物形成过程。
Calcium is a critical element in the global carbon cycle due to its role in carbon sequestration via silicate weathering and carbonate formation. Here we apply calcium (δ44/40Ca) and strontium (87Sr/86Sr) isotopes to explore such chemical weathering processes in a river system draining a diverse range of geologic and climatic environments: the Yalong River, China, and its tributaries. This river originates on the Tibetan Plateau and represents one of the upper reaches of the Changjiang River, China. The Ca isotopic composition of the dissolved load of the Yalong River ranges from 0.60‰ to 1.02‰ (relative to the NIST standard SRM 915a). Higher δ44/40Ca values were found in the plateau and lowland rivers, with lower values in the mountainous rivers. Correlations between riverine dissolved δ44/40Ca values, Sr/Ca ratios, and calcite saturation index indicate that the precipitation of secondary carbonates governs the Ca isotopic composition and carbon transformation in most of this river system. However, such correlations are not seen in the lowland tributaries, where the relationship between δ44/40Ca and lithium (Li) isotopes instead suggests a control by topography and climate, via secondary clay mineral formation. Specifically, heavy rainfall in the lowland regions lowers the pH of the soil solution, which inhibits the precipitation of secondary carbonates. In addition, the flat terrain and thick soils increase the time for water-rock interaction, which favours the formation of secondary clay minerals that preferentially incorporate the lighter Ca isotopes. Overall, this study highlights the potential of stable Ca isotopes, when used in combination with other isotope systems (e.g. Sr and Li isotopes), to quantify secondary mineral formation processes in large river basins.