Behaviour of Sr, Ca, and Mg isotopes under variable hydrological conditions in high-relief large river systems
Behaviour of Sr, Ca, and Mg isotopes under variable hydrological conditions in high-relief large river systems
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DOI：
10.1016/j.gca.2023.01.003
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发表时间：
2023-02
影响因子：
5
通讯作者：
Bei Chen;Si‐Liang Li;Philip A. E. Pogge von Strandmann;David J. Wilson;J. Zhong;Tingting Ma;Jian Sun-Jian
中科院分区：
文献类型：
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作者：
Bei Chen;Si‐Liang Li;Philip A. E. Pogge von Strandmann;David J. Wilson;J. Zhong;Tingting Ma;Jian Sun-Jian
为了评估大型高起伏河流系统的化学风化过程对气候变化的响应，我们研究了青藏高原东南部的金沙江和雅砻江的放射性锶（87 Sr/86 Sr）和稳定钙（δ44/40 Ca）和镁（δ 26 Mg）同位素的季节变化。在低径流季节，与流量（Q）< 2000 m3/s，河流沃茨反映的Sr，Ca和Mg同位素特征的补给融水，与额外的同位素分馏信号的Ca和Mg有关的次生矿物沉淀，这可能意味着融水冲洗土壤溶液从土壤。在中等径流区间（2000 m3/s < Q < 4000 m3/s），金沙江沃茨的Sr、Ca、Mg同位素特征与源头沃茨相似，均受蒸发岩溶解作用的影响，而雅砻江受碳酸盐风化作用的影响大于硅酸盐风化作用。在这两条河流中，基岩溶解控制着河水沃茨的化学成分。在高径流季节（Q > 4000 m3/s），风暴产生快速的地表径流，将大量土壤转移到河流中，因此土壤风化在调节河流化学成分方面发挥着重要作用。此时，河流Ca和Sr同位素演化受次生矿物溶解和沉积物-水阳离子交换的影响。总体而言，这项研究突出了结合多种同位素系统（锶，钙，镁）的潜力，以跟踪在可变的水文条件下的水-岩相互作用的动态。
To assess how chemical weathering processes in large high-relief river systems respond to climatic variability, we studied seasonal changes in radiogenic strontium (87Sr/86Sr) and stable calcium (δ44/40Ca) and magnesium (δ26Mg) isotopes in the Jinsha and Yalong rivers, which drain the southeastern Tibetan Plateau. During the low-runoff season, with discharge (Q) < 2000 m3/s, the river waters reflect the Sr, Ca, and Mg isotope signatures of recharge meltwaters, with additional isotope fractionation signals for Ca and Mg related to secondary mineral precipitation, which might imply that meltwater flushes soil solutions from the soil. During medium-runoff intervals (2000 m3/s < Q < 4000 m3/s), the Sr, Ca, and Mg isotope signatures in the Jinsha river waters are similar to those of the headwaters, which are influenced by evaporite dissolution, while the Yalong is affected by greater carbonate weathering relative to silicate weathering. In both rivers, bedrock dissolution governs the chemical composition of the river waters. During the high-runoff season (Q > 4000 m3/s), storms generate rapid overland flow, which transfers large volumes of soil into the rivers, such that soil weathering plays an important role in regulating riverine chemical compositions. At these times, the riverine Ca and Sr isotope evolution is influenced by secondary mineral dissolution and sediment–water cation exchange. Overall, this study highlights the potential of combining multiple isotope systems (Sr, Ca, Mg) to trace the dynamics of water–rock interaction under variable hydrological conditions.