On the Origin of Aged Sedimentary Organic Matter Along a River‐Shelf‐Deep Ocean Transect

TitleOn the Origin of Aged Sedimentary Organic Matter Along a River‐Shelf‐Deep Ocean Transect
Publication TypeJournal Article
Year of Publication2019
AuthorsBao, R, Zhao, M, McNichol, A, Wu, Y, Guo, X, Haghipour, N, Eglinton, TI
JournalJournal of Geophysical Research: Biogeosciences
Pagination2582 - 2594
Date PublishedJun-08-2021
KeywordsCarbon cycle, hydrodynamic processes, organic carbon, radiocarbon, sediments

To assess the influences of carbon sources and transport processes on the C-14 age of organic matter (OM) in continental margin sediments, we examined a suite of samples collected along a river-shelf-deep ocean transect in the East China Sea (ECS). Ramped pyrolysis-oxidiation was conducted on suspended particulate matter in the Yangtze River and on surface sediments from the ECS shelf and northern Okinawa Trough. C-14 ages were determined on OM decomposition products within different temperature windows. These measurements suggest that extensive amounts of pre-old (i.e., millennial age) organic carbon (OC) are subject to degradation within and beyond the Yangtze River Delta, and this process is accompanied by an exchange of terrestrial and marine OM. These results, combined with fatty acid concentration data, suggest that both the nature and extent of OM preservation/degradation as well as the modes of transport influence the C-14 ages of sedimentary OM. Additionally, we find that the age of (thermally) refractory OC increases during across-shelf transport and that the age offset between the lowest and highest temperature OC decomposition fractions also increases along the shelf-to-trough transect. Amplified interfraction spread or C-14 heterogeneity is the greatest in the Okinawa Trough. Aged sedimentary OM across the transect may be a consequence of several reasons including fossil OC input, selective degradation of younger OC, hydrodynamic sorting processes, and aging during lateral transport. Consequently, each of them should be considered in assessing the C-14 results of sedimentary OM and its implications for the carbon cycle and interpretation of sedimentary records.

URL https://doi.org/10.1029/2019JG005107