Dimensions of radiocarbon variability within sedimentary organic matter

Bao, R., McNichol, A. P., McIntyre, C. P. , Xu, L. and Eglinton, T. I. (2018) Dimensions of radiocarbon variability within sedimentary organic matter. Radiocarbon, 60(03), pp. 775-790. (doi: 10.1017/RDC.2018.22)

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Organic carbon (OC) radiocarbon (14C) signatures in marine surface sediments are highly variable and the causes of this heterogeneity remain ambiguous. Here, we present results from a detailed 14C-based investigation of an Arabian Sea sediment, including measurements on organic matter (OM) in bulk sediment, specific grain size fractions, and OC decomposition products from ramped-pyrolysis-oxidation (RPO). Our results show that 14C ages of OM increase with increasing grain size, suggesting that grain size is an important factor controlling the 14C heterogeneity in marine sediments. Analysis of RPO decomposition products from different grain size fractions reveals an overall increase in age of corresponding thermal fractions from finer to coarser fractions. We suggest that hydrodynamic properties of sediment grains exert the important control on the 14C age distribution of OM among grain size fractions. We propose a conceptual model to account for this dimensionality in 14C variability that invokes two predominant modes of OM preservation within different grain size fractions of Arabian Sea sediment: finer (<63 µm) fractions are influenced by OM-mineral grain aggregation processes, giving rise to relatively uniform 14C ages, whereas OM preserved in coarser (>63 µm) fractions includes materials encapsulated within microfossils and/or entrained fossil (14C-depleted) OC hosted in detrital mineral grains. Our findings highlight the value of RPO for assessment of 14C age variability in sedimentary OC, and for assessing mechanisms of OM preservation in aquatic sediments.

Item Type:Articles
Additional Information:This study was supported by Doc. Mobility fellowship (No. P1EZP2_159064) (R. B.) from the Swiss National Science Foundation (SNSF). This work was also supported by SNSF “CAPS-LOCK” project 200021_140850 (T. I. E.). Additional funding came from a U.S. National Science Foundation Cooperative Agreement (OCE 0753487).
Glasgow Author(s) Enlighten ID:Mcintyre, Dr Cameron
Authors: Bao, R., McNichol, A. P., McIntyre, C. P., Xu, L., and Eglinton, T. I.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Radiocarbon
Publisher:Cambridge University Press
ISSN (Online):1945-5755
Published Online:30 May 2018

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