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The fate of fluvially-deposited organic carbon during transient floodplain storage

Scheingross, J.S. and Repasch, M.N. and Hovius, N. and Sachse, D. and Lupker, M. and Fuchs, M. and Halevy, I. and Gröcke, D.R. and Golombek, N.Y. and Haghipour, N. and Eglinton, T.I. and Orfeo, O. and Schleicher, A.M. (2021) 'The fate of fluvially-deposited organic carbon during transient floodplain storage.', Earth and Planetary Science Letters, 561 . p. 116822.

Abstract

CO2 release from particulate organic carbon (POC) oxidation during fluvial transit can influence climate over a range of timescales. Identifying the mechanistic controls on such carbon fluxes requires determining where POC oxidation occurs in river systems. While field data show POC oxidation and replacement moving downstream in lowland rivers, flume studies show that oxidation during active fluvial transport is limited. This suggests that most fluvial POC oxidation occurs during transient floodplain storage, but this idea has yet to be tested. Here, we isolate the influence of floodplain storage time on POC oxidation by exploiting a chronosequence of floodplain deposits above the modern groundwater table in the Rio Bermejo, Argentina. Measurements from 15 floodplain cores with depositional ages from 1 y to 20 ky show a progressive POC concentration decrease and 13C-enrichment with increasing time spent in floodplain storage. These results from the Rio Bermejo indicate that over 80% of fluvially-deposited POC can be oxidized over millennial timescales in aerated floodplains. Furthermore, POC in the oldest floodplain cores is more 14C-enriched than expected based on the independently-dated floodplain ages, indicating that a portion of this oxidized POC is replaced by autochthonous POC produced primarily by floodplain vegetation. We suggest floodplain storage timescales control the extent of oxidation of fluvially-deposited POC, and may play a prominent role in determining if rivers are significant atmospheric CO2 sources.

Item Type:Article
Full text:Publisher-imposed embargo until 24 February 2022.
(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives 4.0.
File format - PDF
(2373Kb)
Full text:Publisher-imposed embargo until 24 February 2022.
(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives 4.0.
File format - PDF (Supplementary information)
(2639Kb)
Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.epsl.2021.116822
Publisher statement:© 2021 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Date accepted:11 February 2021
Date deposited:12 May 2021
Date of first online publication:24 February 2021
Date first made open access:24 February 2022

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