K isotopes as a tracer for continental weathering and geological K cycling

The causal effects among uplift, climate, and continental weathering cannot be fully addressed using presently available geochemical proxies. However, stable potassium (K) isotopes can potentially overcome the limitations of existing isotopic proxies. Here we report on a systematic investigation of...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 116; no. 18; pp. 8740 - 8745
Main Authors Li, Weiqiang, Beard, Brian L., Raymo, Maureen E., Chen, Jun
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 30.04.2019
Subjects
Aqueous solutions
Basins
Cycles
Drainage
Drainage basins
Fluxes
Isotope composition
Isotopes
Lithology
Mass balance
Modelling
Organic chemistry
Physical Sciences
Rivers
Runoff
Seawater
Sediment load
Sediments
Tributaries
Uplift
Weathering
rivers
fractionation
K isotopes
K cycling
continental weathering
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Summary:The causal effects among uplift, climate, and continental weathering cannot be fully addressed using presently available geochemical proxies. However, stable potassium (K) isotopes can potentially overcome the limitations of existing isotopic proxies. Here we report on a systematic investigation of K isotopes in dissolved load and sediments from major rivers and their tributaries in China, which have drainage basins with varied climate, lithology, and topography. Our results show that during silicate weathering, heavy K isotopes are preferentially partitioned into aqueous solutions. Moreover, δ 41K values of riverine dissolved load vary remarkably and correlate negatively with the chemical weathering intensity of the drainage basin. This correlation allows an estimate of the average K isotope composition of global riverine runoff (δ 41K = −0.22‰), as well as modeling of the global K cycle based on mass balance calculations. Modeling incorporating K isotope mass balance better constrains estimated K fluxes for modern global K cycling, and the results show that the δ 41K value of seawater is sensitive to continental weathering intensity changes. Thus, it is possible to use the δ 41K record of paleo-seawater to infer continental weathering intensity through Earth’s history.
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Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved March 22, 2019 (received for review June 30, 2018)
Author contributions: S.L., W.L., Y.C., and J.C. designed research; S.L., W.L., and X.W. performed research; W.L. and B.L.B. contributed new reagents/analytic tools; S.L., W.L., B.L.B., and M.E.R. analyzed data; and S.L. and W.L. wrote the paper.
ISSN:0027-8424
1091-6490
1091-6490
DOI:10.1073/pnas.1811282116