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Title: High rates of rock organic carbon oxidation sustained as Andean sediment transits the Amazon foreland-floodplain
The oxidation of organic carbon contained within sedimentary rocks (“petrogenic” carbon, or hereafter OCpetro) emits nearly as much CO2as 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 OCpetrooxidation. However, these settings also export unweathered material that may continue to react in downstream floodplains. The relative importance of OCpetrooxidation 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 OCpetrooxidation from the Andes to the Amazon floodplain using a common approach. Dissolved rhenium concentrations (n = 131) range from 0.01 to 63 pmol L−1and vary depending on lithology and geomorphic setting. We find that >75% of the dissolved Re derives from OCpetrooxidation and that this proportion increases downstream. We estimate that in the Andes, OCpetrooxidation releases 11.2+4.5/−2.8tC km−2y−1of CO2, which corresponds to ~41% of the total OCpetrodenudation (sum of oxidized and solid OCpetro). A Re mass balance across the Rio Madre de Dios shows that 46% of OCpetrooxidation takes place in the Andes, 14% in the foreland-lowlands, and 40% in the Andean-fed floodplains. This doubling of OCpetrooxidation flux downstream of the Andes demonstrates that, when present, floodplains can greatly increase OCpetrooxidation and CO2release.  more » « less
Award ID(s):
1851309
PAR ID:
10587669
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Publisher / Repository:
PNAS
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
120
Issue:
39
ISSN:
0027-8424
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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