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  • 1
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    Radiocarbon constraint on relict organic carbon contributions to Ross Sea sediments (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q04012, doi:10.1029/2005GC001097.
    Description: We estimate the relative contribution of relict organic matter to the acid-insoluble organic carbon (AIOC) fraction of surface sediments from Ross Sea, Antarctica, on the basis of 14C abundance. The bulk isotopic characteristics of AIOC can largely be explained by simple two-source models of modern and relict organic carbon, when samples are grouped according to two geographical regions, namely, southwestern and south central Ross Sea. This spatial variability in relict organic carbon could be controlled by proximity to the edge of the Ross Ice Shelf and ice drainage areas. Radiocarbon abundance in the AIOC is potentially an excellent tool to estimate the contribution of relict organic carbon in the Antarctic margin sediments.
    Description: This work was partly supported by a grant from Japan Society for the Promotion of Science to N.O.
    Keywords: Ross Sea ; Radiocarbon ; Sediment ; Organic carbon
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    The radiocarbon age of organic carbon in marine surface sediments (2010)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 74 (2010): 6788-6800, doi:10.1016/j.gca.2010.09.001.
    Description: Long-term carbon cycling and climate change are strongly dependent on organic carbon (OC) burial in marine sediments. Radiocarbon (14C) has been widely used to constrain the sources, sinks, and processing of sedimentary OC. To elucidate the dominant controls on the radiocarbon content of total organic carbon (14CTOC) accumulating in surface sediments we construct a box model that predicts 14CTOC in the sediment mixed layer (measured as fraction modern, Fm). Our model defines three distinct OC pools (“degradable,” “semi-labile,” and “refractory”) and assumes that 14CTOC flux to sediments is exclusively derived from surface ocean primary productivity, and hence follows a “generic” surface ocean dissolved inorganic carbon (DIC) bomb curve. Model predictions are compared to a set of 75 surface sediment samples, which span a wide geographic range and reflect diverse water column and depositional conditions, and for which sedimentation rate and mixed layer depth are well characterized. Our model overestimates the Fm value for a majority (65%) of these sites, especially at shallow water depths and for sites characterized by depleted δ13CTOC values. The model is most sensitive to sedimentation rate and mixed-layer depth. Therefore, slight changes to these parameters can lead to a match between modeled and measured Fm values at many sites. Because of model sensitivity, slight changes in sedimentation rate and mixed layer depth can allow predictions to match measured Fm at many sites. Yet, in some cases, we find that measured Fm values cannot be simulated without large and unrealistic changes to sedimentation rate and mixed layer depth. These results point to sources of pre-aged OC to surface sediments and implicate soil-derived terrestrial OC, reworked marine OC, and/or anthropogenic carbon as important components of the organic matter present in surface sediments. This approach provides a valuable framework within which to explore controls on sedimentary organic matter composition and carbon burial over a range of spatial and temporal scales.
    Description: This work was supported by NSF grants OCE-0526389 (W. Martin), OCE-0851350 and OCE-0402533 (T. Eglinton), as well as WHOI Senior Scientist Chair and Independent Study Award funds (T. Eglinton).
    Keywords: Radiocarbon ; C-14 ; Organic carbon ; Marine sediments ; Box model ; Global carbon cycle
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 3
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    Spatiotemporal variation of the quality, origin, and age of particulate organic matter transported by the Yangtze River (Changjiang) (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 123 (2018): 2908-2921, doi:10.1029/2017JG004285.
    Description: Information on the age dynamics of particulate organic matter (POM) in large river systems is currently sparse and represents an important knowledge gap in our understanding of the global carbon cycle. Here we examine variations in organic geochemical characteristics of suspended sediments from the Changjiang (Yangtze River) system collected between 1997 and 2010. Higher particulate organic carbon content (POC%) values were observed in the middle reach, especially after 2003, and are attributed to the increase of in situ (aquatic) primary production associated with decreased total suspended matter concentrations. Corresponding Δ14C values from depth profiles taken in 2009 and 2010 indicate spatial and temporal variations in POC sources within the basin. Two isotopic mass balance approaches were explored to quantitatively apportion different sources of Changjiang POM. Results indicate that contributions of biomass and pre‐aged soil organic matter are dominant, regardless of hydrological conditions, with soil‐derived organic carbon comprising 17–56% of POC based on a Monte Carlo three‐end‐member mixing model. In contrast, binary mixing model calculations suggest that up to 80% of POC (2009 samples only) derived from biospheric sources. The emplacement of the Three Gorges Dam and resulting trapping of sediment from the upper reach of the watershed resulted in a modification of POM 14C ages in the reservoir. With the resulting decline in sediment load and increase in the proportion of modern POC in the lower reach, these changes in POM flux and composition of the Changjiang have significant implications for downstream carbon cycle processes.
    Description: Natural Science Foundation of China Grant Numbers: 41530960, 41276081
    Description: 2019-03-15
    Keywords: Organic carbon ; Changjiang ; Radiocarbon ; Suspended particulate matter ; Three Gorges Dam
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Influence of hydraulic connectivity on carbon burial efficiency in Mackenzie Delta lake sediments (2021)
    American Geophysical Union
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    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Lattaud, J., Broder, L., Haghipour, N., Rickli, J., Giosan, L., & Eglinton, T., I. Influence of hydraulic connectivity on carbon burial efficiency in Mackenzie Delta lake sediments. Journal of Geophysical Research: Biogeosciences, 126(3), (2021): e2020JG006054, https://doi.org/10.1029/2020JG006054.
    Description: The Arctic is undergoing accelerated changes in response to ongoing modifications to the climate system, and there is a need for local to regional scale records of past climate variability in order to put these changes into context. The Mackenzie Delta region in northern Canada is populated by numerous small shallow lakes. They are classified as no-, low-, and high-closure (NC, LC, and HC, respectively) lakes, reflecting varying degrees of connection to the river main stem, and have different sedimentation characteristics. This study examines sedimentological (mineral surface area, grain size), carbon isotopic (bulk and molecular-level) and inorganic isotopic (neodymium) characteristics of sediment cores from three lakes representing each class. We find that HC lake sediments exhibit strikingly different properties from the other lake sediments. Specifically, they are characterized by higher organic carbon loadings per unit mineral surface area and with relatively minor influence from allochthonous, petrogenic (rock-derived) organic carbon. In contrast, LC and NC lakes have the potential to record basin-scale climatic changes at a high resolution by virtue of enhanced detrital sedimentation. Overall the delta lakes have the capacity to bury about 2 MtC year−1, with little changes in the last 200 years. However, in the (near) future, an increased number of high closure lakes might change the carbon burial efficiency of the Mackenzie Delta as they seem to retain less carbon than NC and LC lakes.
    Description: J. Lattaud was funded by a Rubicon grant (019.183EN.002) from NWO, Netherlands Organization for scientific research.
    Keywords: Bulk radiocarbon ; Carbon isotopes ; Mackenzie Delta ; Mineral loading ; N-alkanes
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    On the origin of aged sedimentary organic matter along a river-shelf-deep ocean transect (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 124(8), (2019): 2582-2594, doi: 10.1029/2019JG005107.
    Description: To assess the influences of carbon sources and transport processes on the 14C 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. 14C 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 14C 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 14C 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 14C results of sedimentary OM and its implications for the carbon cycle and interpretation of sedimentary records.
    Description: This study was supported by Doc. Mobility Fellowship (P1EZP2_159064; R. B.) from the Swiss National Science Foundation (SNSF). This study was also supported by SNF “CAPS‐LOCK” project 200021_140850 (T. I. E.), by the National Natural Science Foundation of China (NSFC; grants 41520104009 and 41630966, M. Z.), and by the “111” project (B13030). We are grateful for support of the NOSAMS staff in the execution of this project. We also appreciate the assistance from Yushuang Zhang (Ocean University of China) at NOSAMS and members of the Laboratory for Ion Beam Physics at ETH Zurich for AMS measurements. We acknowledge Lei Xing, Haidong Zhang, Guodong Song, Meng Yu, Yonghao Jia, and Shanshan Duan (Ocean University of China) for sampling assistance on the cruises. Assistance at sea by the crews of R/V Dongfanghong II and R/V Hakuhu Maru is also acknowledged. Readers can access or find the data from figures and tables in the supporting information.
    Keywords: Radiocarbon ; Carbon cycle ; Sediments ; Organic carbon ; Hydrodynamic processes
    Repository Name: Woods Hole Open Access Server
    Type: Article
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