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    Ca isotope constraints on chemical weathering processes: evidence from headwater in the Changjiang River, China

    Chen, B. and Li, S. and Pogge von Strandmann, Philip and Sun, J. and Zhong, J. and Li, C. and Ma, T. and Xu, S. and Liu, C. (2019) Ca isotope constraints on chemical weathering processes: evidence from headwater in the Changjiang River, China. Chemical Geology 531 , p. 119341. ISSN 0009-2541.

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    Abstract

    This study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds. We chose to study the Jinsha River, which originates from the Tibetan Plateau and also is in the upper reaches of the Changjiang River. Analysis of hydrochemistry, radiogenic strontium isotope and stable calcium isotopes were conducted of the Jinsha River water samples, which were collected along its mainstream and main tributaries in the summer. The results show that the water chemistry of the mainstream waters is dominated by evaporite weathering, which have low 87Sr/86Sr values (0.7098–0.7108) and wide range of Sr contents (2.70–9.35 μmol/L). In contrast, tributaries of the Jinsha River have higher 87Sr/86Sr (0.7090–0.7157) and lower Sr contents (∼1 μmol/L). Moreover, the Ca isotopic compositions in the mainstream (0.87–1.11‰) are heavier than the tributaries (0.68–0.88‰) and could not be fully explained by the conventional mixing of different sources. We suggest that secondary carbonate precipitation fractionates Ca isotopes in the Jinsha River, and fractionation factors are between 0.99935 and 0.99963. At least 66% of Ca was removed in the mainstream of the Jinsha River through secondary mineral precipitation, and the average value is ∼35% in the tributaries. The results highlight that evaporite weathering results in more carbonate precipitation influencing Ca transportation and cycling in the riverine system constrained by stable Ca isotopic compositions and water chemistry.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): Ca isotopes, Chemical weathering, Secondary carbonate precipitation, Isotope fractionation, Tibetan plateau
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Philip Pogge Von Strandmann
    Date Deposited: 25 Nov 2019 15:32
    Last Modified: 26 Nov 2019 03:35
    URI: http://eprints.bbk.ac.uk/id/eprint/30038

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