Conservative composition of n-alkane biomarkers in Sphagnum species : implications for palaeoclimate reconstruction in ombrotrophic peat bogs.

Abstract

The n-alkane distributions from total lipid extracts of ten modern Sphagnum moss species, collected from a suite of ombrotrophic bogs across Europe, were determined using gas chromatography/mass spectrometry (GC/MS). n-Alkane distributions are reported for the first time for Sphagnum balticum, S. majus, S. angustifolium and S. lindbergii, which are all dominated by C23 with the exception of S. lindbergii, which exhibits a bimodal distribution with C23 and C31 as the major homologues. The distributions for individual species generally agree with published compositions, confirming the conservative nature of the n-alkane compositions, which provide a basis for differentiating the n-C23 and n-C25 dominated species. Investigations of the variation in n-C23/n-C25 and n-C23/n-C31 ratios of Sphagnum species, using the new and published n-alkane distributions, reveal that intra-species variation is generally minor. Critically, the distributions and ratios for most species do not vary among the sites studied, suggesting that they are conservative tracers for a given species, despite differences in growth conditions. In contrast, inter-species variation exists, allowing differentiation of individual Sphagnum species based on vegetation biomarkers, specifically the C25n-alkane in S. fuscum and the n-C23/n-C25 ratio. Biomarker stratigraphic analysis of a 150 cm peat core (Kontolanrahka Bog, Finland) reveal shifts in the n-C23/n-C25 ratio, which track changes in the abundance of S. fuscum in the macrofossil record. This supports the application of n-alkane biomarkers in peat archives for tracking past shifts in individual Sphagnum species abundance. This will be particularly important where fossil plant remains are highly degraded in, or absent from, peat records.