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Published August 15, 2017 | Published + Supplemental Material
Journal Article Open

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

Abstract

Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO_2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO_2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO_2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO_2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O_2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

Additional Information

© 2017 National Academy of Sciences. Edited by Thure E. Cerling, University of Utah, Salt Lake City, UT, and approved July 5, 2017 (received for review February 21, 2017). Published online before print July 31, 2017. We thank three reviewers for constructive comments. M.A.T. was supported by a University of Southern California College Merit Fellowship and a Caltech Texaco Postdoctoral Fellowship, N.M. by a Deutscher Akademischer Austauschdienst exchange fellowship, J.H. by the German Science Foundation (DFG-project HA4472/6-1 and the Cluster of Excellence "CliSAP," EXC177, Universität Hamburg) and Bundesministerium für Bildung und Forschung Project PALMOD (Ref 01LP1506C), and A.J.W. by National Science Foundation Grant EAR-1455352. Requests for access to the GloRiCh database should be addressed to J. Hartmann at geo@hattes.de. Author contributions: N.M., J.H., and A.J.W. designed research; M.A.T., N.M., and J.H. performed research; M.A.T. and J.F.A. contributed new reagents/analytic tools; M.A.T., N.M., J.H., J.F.A., and A.J.W. analyzed data; and M.A.T. and A.J.W. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702953114/-/DCSupplemental.

Attached Files

Published - PNAS-2017-Torres-8716-21.pdf

Supplemental Material - pnas.1702953114.sapp.pdf

Supplemental Material - pnas.1702953114.sd01.xlsx

Supplemental Material - pnas.1702953114.sd02.xlsx

Supplemental Material - pnas.1702953114.sd03.xlsx

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August 22, 2023
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