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C/N, δ13C and δ15N as paleoenvironmental proxies The analysis of organic matter (OM) from modern and paleoenvironmental settings has contributed to the understanding of the carbon biogeochemical cycle at a variety of spatial and temporal scales. Specifically, the concentrations of carbon (C) and nitrogen (N), from which the C/N ratio is derived, and stable C and N isotopes (12C/13C, quoted as δ13C relative to Vienna Pee Dee Belemnite (V-PDB) and; 14N/15N, quoted as δ15N relative to N2-AIR) of OM have been used to understand processes from biological productivity through to paleoenvironmental interpretations. For example, C/N ratios are widely used as an indicator of OM origin (C/N < 10 interpreted as aquatic; C/N > 20 as terrestrial source) and δ13C can be used to, among other things, understand broad-scale changes in vegetation type (e.g., photosynthetic pathways; C3 and C4 plant types; Smith and Epstein, 1971; Meyers, 1997; 2003; Sharpe, 2007). δ15N has also been used to investigate OM origin (Thornton and McManus, 1994; Meyers, 1997; Hu et al., 2006), but is more commonly used to understand nitrate utilization, denitrification and N deposition in aquatic systems (e.g., Altabet et al., 1995). These interpretations are based on the assumption that we can reliably determine C/N, δ13C and δ15N values in OM.

Evidence for bias in C/N, δ13C and δ15N values of aquatic and terrestrial organic materials due to acid pre-treatment methods