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Weak impact of landscape parameters and rock lithology on Mg isotope composition of the Yenisey River and its tributaries
Chemical Geology ( IF 3.9 ) Pub Date : 2020-05-01 , DOI: 10.1016/j.chemgeo.2020.119547
Vasileios Mavromatis , Anatoly S. Prokushkin , Mikhail A. Korets , Jérôme Chmeleff , Stéphanie Mounic , Oleg S. Pokrovsky

Abstract Constraining the mechanisms controlling the riverine flux of major cations and their isotopes including that of Mg to the World Ocean is one of the challenges in Earth surface isotope geochemistry. In an attempt to identify the main factors affecting the Mg isotopic composition of large rivers including vegetation, climate and lithology of the watershed, we studied the largest, in terms of discharge, Siberian river, Yenisey, and 20 of its main tributaries, during spring flood, summer flow and winter. The working hypothesis was that the influence of bedrock composition is most pronounced in winter, when the soils are frozen and the rivers are fed by deep underground waters. Thus, we anticipated that the presence of permafrost will help to distinguish the impact of surface processes, linked to biological uptake and release, and deep soil/underground transport of Mg from mineral sources. In contrast to these expectations, no sizable differences in the Mg isotope composition of the river water (±0.1‰) for both the Yenisey tributaries and its main channel has been observed between the spring flood (May) and the winter (March) period. Those two periods are characterized by the differences of discharge and degree of lithological impact on element source in the river water. Regardless of the season, there was no straightforward control of lithology (relative abundance of carbonates, basalts, granites and sedimentary rocks) on δ26Mg in the main tributaries of the Yenisey river. Our findings suggest that the use of riverine Mg isotope signature for tracing weathering mechanisms and dominant lithological impact is not straightforward at the scale of large rivers whose watersheds present multiple lithologies, variable climatic conditions and vegetation types.

中文翻译:

景观参数和岩石岩性对叶尼塞河及其支流镁同位素组成的微弱影响

摘要 限制主要阳离子及其同位素(包括镁)向世界海洋的河流通量的控制机制是地球表面同位素地球化学的挑战之一。为了确定影响大河流镁同位素组成的主要因素,包括流域的植被、气候和岩性,我们研究了春季最大的西伯利亚河、叶尼塞河及其 20 条主要支流。洪水,夏季流量和冬季。工作假设是基岩成分的影响在冬季最为明显,此时土壤结冰,河流由深层地下水补给。因此,我们预计永久冻土的存在将有助于区分与生物吸收和释放相关的地表过程的影响,和矿物源中镁的深层土壤/地下运输。与这些预期相反,在春季洪水(5 月)和冬季(3 月)期间,叶尼塞支流及其主要河道的河水 Mg 同位素组成没有显着差异 (±0.1‰)。这两个时期的特点是流量不同,岩性对河水中元素源的影响程度不同。无论季节如何,叶尼塞河主要支流中的 δ26Mg 都没有直接控制岩性(碳酸盐、玄武岩、花岗岩和沉积岩的相对丰度)。
更新日期:2020-05-01
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