Lipid biomarker, δ13C and plant macrofossil stratigraphy of a Scottish montane peat bog over the last two millennia

Seven horizons of a peat core covering the last 2000 years from Moine Mhor, a blanket bog in the Cairngorm Mountains, Scotland have been examined for the carbon number distributions of the long-chain hydrocarbon, alcohol and acid components using gas chromatography (GC) and gas chromatography—mass spectrometry (GC—MS). Compound specific δ13C values for individual n-alkanes were obtained, using gas chromatography—isotope ratio mass spectrometry (GC—irms). The lipid biomarker distributions and the δ13C values have been compared with those of eleven species of living plant dominant at the contemporary surface of the bog. The observed lipid stratigraphy shows only partial agreement with that calculated using macrofossil abundance data and the lipid distributions for the living taxa, a result which reflects the inherent uncertainties in both the lipid biomarker and the macrofossil approaches to palaeoenvironmental stratigraphy. The carbon isotope values for the individual n-alkanes of the plants (−27.6 to −36.6‰) and of the peat layers (−29 to −31.7‰) are as expected for the C3 photosynthetic pathway. However, the n-alkanes from the surface samples were more depleted (by 2‰) in 13C than those from the rest of the core, a negative shift which may, in part, reflect the shift (−1.2‰) in δ13C estimated for CO2 in a pre-industrialised to an industrialised atmosphere.