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| Titel |
Sr isotopic characteristics in two small watersheds draining silicate and carbonate rocks: implication for studies on seawater Sr isotopic evolution |
| VerfasserIn |
W. H. Wu, H. B. Zheng, J. H. Cao, J. D. Yang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 2 ; Nr. 18, no. 2 (2014-02-13), S.559-573 |
| Datensatznummer |
250120277
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| Publikation (Nr.) |
 copernicus.org/hess-18-559-2014.pdf |
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| Zusammenfassung |
We systematically investigated the Sr isotopic characteristics of a small
silicate watershed, the Xishui River a tributary of the Yangtze River, and a
small carbonate watershed, the Guijiang River a tributary of the Pearl River.
The results show that the two rivers have uncommon Sr isotopic
characteristics compared with most small watersheds. Specifically, the
silicate watershed (Xishui River) has relatively high Sr concentrations
(0.468 to 1.70 μmol L−1 in summer and 1.30 to 3.17 μmol L−1 in winter,
respectively) and low 87Sr/86Sr ratios (0.708686 to 0.709148 in
summer and 0.708515 to 0.709305 in winter). The carbonate watershed
(Guijiang River) has low Sr concentrations (0.124 to 1.098 μmol L−1) and
high 87Sr/86Sr ratios (0.710558 to 0.724605).
As the 87Sr/86Sr ratios in the Xishui River are lower than those
in seawater, the 87Sr/86Sr ratio of seawater will decrease after
the river water is transported to the oceans. Previous studies have also
shown that some basaltic watersheds with extremely high chemical weathering
rates reduced the seawater Sr isotope ratios. In other words, river
catchments with high silicate weathering rates do not certainly transport
highly radiogenic Sr into oceans. Therefore, the use of the variations in
the seawater 87Sr/86Sr ratio to indicate the continental
silicate weathering intensity may be questionable.
In the Guijiang River catchment, the 87Sr/86Sr ratios of carbonate
rocks and other sources (rainwater, domestic and industrial waste water, and
agricultural fertilizer) are lower than 0.71. In comparison, some
non-carbonate components, such as sand rocks, mud rocks, and shales, have
relatively high Sr isotopic compositions. Moreover, granites accounted for
only 5% of the drainage area have extremely high 87Sr/86Sr
ratios with an average of greater than 0.8. Therefore, a few silicate
components in carbonate rocks obviously increase the Sr isotopic
compositions of the river water. |
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