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High rates of rock organic carbon oxidation sustained as Andean sediment transits the Amazon foreland-floodplain

Dellinger, Mathieu; Hilton, Robert G.; Baronas, J. Jotautas; Torres, Mark A.; Burt, Emily I.; Clark, Kasey E.; Galy, Valier; Ccahuana Quispe, Adan Julian; West, A. Joshua

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Authors

Mathieu Dellinger

Robert G. Hilton

Mark A. Torres

Emily I. Burt

Kasey E. Clark

Valier Galy

Adan Julian Ccahuana Quispe

A. Joshua West



Abstract

The oxidation of organic carbon contained within sedimentary rocks (“petrogenic” carbon, or hereafter OCpetro) emits nearly as much CO2 as is released by volcanism, thereby playing a key role in the long-term global C budget. High erosion rates in mountains have been shown to increase OCpetro oxidation. However, these settings also export unweathered material that may continue to react in downstream floodplains. The relative importance of OCpetro oxidation in mountains versus floodplains remains difficult to assess as disparate methods have been used in the different environments. Here, we investigate the sources and fluxes of rhenium (Re) in the Rio Madre de Dios to quantify OCpetro oxidation from the Andes to the Amazon floodplain using a common approach. Dissolved rhenium concentrations (n = 131) range from 0.01 to 63 pmol L−1 and vary depending on lithology and geomorphic setting. We find that >75% of the dissolved Re derives from OCpetro oxidation and that this proportion increases downstream. We estimate that in the Andes, OCpetro oxidation releases 11.2+4.5/−2.8 tC km−2 y−1 of CO2, which corresponds to ~41% of the total OCpetro denudation (sum of oxidized and solid OCpetro). A Re mass balance across the Rio Madre de Dios shows that 46% of OCpetro oxidation takes place in the Andes, 14% in the foreland-lowlands, and 40% in the Andean-fed floodplains. This doubling of OCpetro oxidation flux downstream of the Andes demonstrates that, when present, floodplains can greatly increase OCpetro oxidation and CO2 release.

Citation

Dellinger, M., Hilton, R. G., Baronas, J. J., Torres, M. A., Burt, E. I., Clark, K. E., …West, A. J. (2023). High rates of rock organic carbon oxidation sustained as Andean sediment transits the Amazon foreland-floodplain. Proceedings of the National Academy of Sciences, 120(39), Article e2306343120. https://doi.org/10.1073/pnas.2306343120

Journal Article Type Article
Acceptance Date Aug 9, 2023
Online Publication Date Sep 19, 2023
Publication Date Sep 26, 2023
Deposit Date Nov 19, 2023
Publicly Available Date Nov 20, 2023
Journal Proceedings of the National Academy of Sciences
Print ISSN 0027-8424
Electronic ISSN 1091-6490
Publisher National Academy of Sciences
Peer Reviewed Peer Reviewed
Volume 120
Issue 39
Article Number e2306343120
DOI https://doi.org/10.1073/pnas.2306343120
Public URL https://durham-repository.worktribe.com/output/1944037

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