Lithium as a Silicate Weathering Proxy: Problems and Perspectives |
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| Authors: | Junyeon Yoon |
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| Institution: | (1) School of Earth and Environmental Sciences, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul, 151-742, Republic of Korea;(2) Present address: Department of Geological Sciences, University of Texas, Austin, TX 78712, USA |
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| Abstract: | The lithium concentration of the dissolved load from the Lena River, together with major element chemistry and GIS-based area
and runoff data demonstrate the importance of evaporites in controlling dissolved Li in river waters. Eighty-four percent
of the Li in the dissolved load of upper Lena tributaries comes from evaporites in these drainage basins. Altogether, at least
~20% of the total Li flux of the Lena River originates from this source. This finding has important implications for using
lithium as a proxy for silicate weathering. The Li flux and the 87Sr/86Sr ratio are compared in order to address a difference between the two silicate weathering rate proxies. The proposed controls
on the dissolved δ7Li values in rivers (kinetic vs. equilibrium isotopic fractionation; Rayleigh-type preferential extraction of the heavy isotope)
(Huh et al., Earth Planet Sci Lett 194:189–199, 2001) are evaluated using data from both the Siberian rivers and the Orinoco
River. Neither of the proposed mechanisms satisfactorily explains the comprehensive data set. Instead, a ‘mineralogy-specific
view’ that emphasizes the difference in the secondary mineralogy (i.e., fractionation factor) is presented as a potential
rationalization in the form of the refined Rayleigh-type extraction. |
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