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There is a known bias in C/N, δ 13 C and δ 15 N values of organic matter (OM) due to preanalysis acid treatment methods. We report here, for the first time, the results of a preanalysis acid treatment method comparison of measured C/N, δ 13 C and δ 15 N values in bulk 16 OM from a sedimentary sequence of samples to illustrate this bias. Here we show that acid 17 treatment significantly reduces the accuracy (between method biases) and precision (within 18 method bias) of C/N, δ 13 C and δ 15 N values of OM, suggesting a differential response of sample OM between methods and sample horizons, and in some cases inefficient removal of 20 inorganic carbon. We show that different methods can significantly influence environmental 21 interpretation in some of our sample horizons (i.e. interpretation of aquatic vs. terrestrial OM 22 source; C 3 vs. C 4 vegetation). Specifically, there are unpredictable and non-linear differences between methods for C/N values in the range of ~ 1-100; δ 13 C values in the range of 0.2-6.8 ‰ and; δ 15 Nvalues in the range of 0.3-0.7 ‰. Importantly, these ranges are mostly much greater than the instrument precision (defined as the standard deviation of replicate analysis of standard reference materials; for this study, ± 0.5 for C/N values, ± 0.1 ‰ for δ 13 C values and; ± 0.1 ‰ for δ 15 N). The accuracy and precision of measured C/N, δ 13 C and δ 15 N values of bulk OM is not just dependent upon environmental variability, but on acid pretreatment, residual inorganic carbon and organic matter state and composition. Collectively, this makes the correlation between samples prepared in different ways, including those from down core reconstructions, highly questionable.

We examined the use of δ13C, TOC and C/N geochemistry of sedimentary organic matter to reconstruct former sea levels and paleoenvironments in the absence of suitable microfossil data. The modern distribution of δ13C, TOC and C/N of 33 vegetation and 74 surface sediment samples collected from four coastal wetlands in the Thames Estuary and Norfolk, UK are described. The δ13C, TOC and C/N geochemistry of sediments varied in relation to the input of in situ vascular vegetation versus allochthonous particulate organic matter and algae, which was controlled primarily by tidal inundation. We reviewed published and unpublished studies to produce an English database of vegetation (n = 257) and sediment (n = 132) δ13C, TOC and C/N geochemistry. Four elevation‐dependent environments in the database had statistically distinct δ13C, TOC and C/N values: (1) tidal flat/low marsh (δ13C: −24.9 ± 1.2‰; TOC: 3.6 ± 1.7%; C/N: 9.9 ± 0.8); (2) middle marsh/high (δ13C: −26.2 ± 1.0‰; TOC: 9.8 ± 6.7%; C/N: 12.1 ± 1.8); (3) reed swamp (δ13C: −27.9 ± 0.7‰: TOC: 36.5 ± 11.5%; C/N: 13.9 ± 1.2); and (4) fen carr (δ13C: −29.0 ± 0.6‰; TOC: 41.6 ± 5.7%; C/N: 17.4 ± 3.1). The δ13C, TOC and C/N geochemistry database was applied to a Holocene sediment core collected from the Thames Estuary to produce three new sea‐level index points and one limiting date, illustrating the utility of δ13C, TOC and C/N values to reconstruct Holocene relative sea levels. Copyright © 2015 John Wiley & Sons, Ltd.