Dataset Information

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

ABSTRACT: 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, ?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 (?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 ?⁴¹K value of seawater is sensitive to continental weathering intensity changes. Thus, it is possible to use the ?⁴¹K record of paleo-seawater to infer continental weathering intensity through Earth's history.

SUBMITTER: Li S

PROVIDER: S-EPMC6500156 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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

Li Shilei S Li Weiqiang W Beard Brian L BL Raymo Maureen E ME Wang Xiaomin X Chen Yang Y Chen Jun J

Proceedings of the National Academy of Sciences of the United States of America 20190415 18

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 sil ...[more]

PMID: 30988182

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Project description:Hydrogen isotope (?2H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with ?13C and ?15N analyses to evaluate complex trophic relationships in aquatic systems. However, ?2H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix-equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, ?2H (and ?15N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007-2010, and were assessed for the effects of species, feeding habits, and ambient water ?2H values. After lipid removal, we used comparative equilibration to calibrate muscle ?2H values to nonexchangeable ?2H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic ?2H enrichment by comparing ?2H values with ?15N values. Our results showed a significant logarithmic correlation between fork length and ?2H values, and no strong relationships between ?15N and ?2H. This suggests the so-called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for ?2H enrichment. We evaluated the importance of water in controlling ?2H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The ?2H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using ?2H measurements.

Dataset Information

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

Publications

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

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