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River discharge influences on particulate organic carbon age structure in the Mississippi/Atchafalaya River System
Author(s) -
Rosenheim Brad E.,
Roe Kimberly M.,
Roberts Brian J.,
Kolker Alexander S.,
Allison Mead A.,
Johannesson Karen H.
Publication year - 2013
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/gbc.20018
Subject(s) - radiocarbon dating , discharge , total organic carbon , environmental science , hydrology (agriculture) , delta , sediment , particulates , drainage basin , river delta , mars exploration program , carbon fibers , geology , environmental chemistry , geomorphology , geography , chemistry , paleontology , physics , materials science , cartography , geotechnical engineering , organic chemistry , aerospace engineering , astronomy , composite number , engineering , composite material
Applying ramped pyrolysis radiocarbon analysis to suspended river sediments, we generate radiocarbon ( 14 C) age spectra for particulate organic carbon (POC) from the lower Mississippi‐Atchafalaya River system (MARS) to better understand a major river system's role in carbon transport. Ramped pyrolysis 14 C analysis generates age distributions of bulk carbon based on thermochemical stability of different organic components. Our results indicate higher proportions of older material in the POC during higher discharge. Ages increase throughout the high‐discharge age spectra, indicating that no single component of the POC is responsible for the overall age increases observed. Instead, older material is contributed across the POC age spectrum and unrelated to increased bedload suspension. In this comparison of 2 spring discharges, less than half of the POC transported during higher discharge is less than 1000 14 C years in age, constraining of the role of the MARS as a flux of atmospheric CO 2 toward longer‐term sedimentary sinks in the Mississippi delta and the Gulf of Mexico. The results suggest that delta‐building processes benefit disproportionately from high discharge events carrying larger amounts of sediment because these events involve both a higher proportion of millennially‐aged carbon from floodplain exchange of POC and a potentially higher proportion of petrogenic carbon (30‐530% increase). Overall, an internally consistent picture of PO 14 C age distributions from a major river system emerges, as differences in space and time are small compared to the range of ages of POC sources in such a large basin.