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In groundwater-fed fen peatlands, the surface biomass decays rapidly and, as a result, highly humified peat is formed. A high degree of humification constrains palaeoecological studies because reliable identification of plant remains is hampered. Organic geochemistry techniques as a means of identifying historical plant communities have been successfully applied to bog peat. The method has also been applied to fen peat, but without reference to the composition of fen plants. We have applied selected organic geochemistry methods to determine the composition of the neutral lipid fractions from 12 living fen plants, to investigate the potential for the distributions to characterize and separate different fen plants and plant groups. Our results show correspondence with previous studies, e.g. C23 and C25n-alkanes dominating Sphagnum spp. and C27 to C31 alkanes dominating vascular plants. However, we also found similarities in n-alkane distributions between Sphagnum spp. and the below ground parts of some vascular plants. We tested the efficiency of different n-alkane ratios to separate species and plant groups. The ratios used for bog studies (e.g. n-C23/n-C25 and n-C23/n-C29) did not work as consistently for fen plants. Some differences in sterol distribution were found between vascular plants and mosses; in general vascular plants had a higher concentration of sterols. When distributions of n-alkanes, n-alkane ratios and sterols were all included as variables, redundancy analysis (RDA) separated different plant groups into their own clusters. Our results imply that the pattern for bog biomarkers cannot directly be applied to fen environments. Nevertheless, they encourage further testing to determine whether or not the identification of plant groups, plants or plant parts from highly humified peat is possible by applying fen species-specific biomarker proxies.

Peat cores provide decadal to centennial records of climatic and environmental change, including evidence for human/environment interaction. Existing palaeoenvironmental proxies (macrofossils, pollen, humification, testate amoebae, lipid composition) require multiple laboratory preparation steps and may be subject to differential preservation that can limit production of a continuous time series. The potential for pyrolysis gas-chromatography–mass-spectrometry (Py–GC–MS) to be applied to bulk peat samples is investigated here. The only preparatory step required was freeze drying. Analysis of a range of important peat-forming plants demonstrates that Sphagnum moss species are unique in containing the pyrolysis product of sphagnum acid, 4-isopropenylphenol. In contrast, non-Sphagnum species are rich in lignin pyrolysis products, which are absent from Sphagnum. The presence of these pyrolysis markers is reflected in bulk peat composition and tested here using archives from Bolton Fell Moss and Butterburn Flow (UK), Kontolanrahka (Finland) and Bissendorfer Moor (Germany). A ratio between 4-isopropenylphenol and two lignin pyrolysis products is proposed as a proxy for total Sphagnum input to peat archives and shows potential for use as a rapid screening tool for characterising bulk peat composition before more intensive analysis.

In order to develop new tools in the reconstruction of microbiological processes in ancient continental settings, we determined the concentration of archaeol and sn -2-hydroxyarchaeol in four Holocene ombrotrophic peatlands, spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal water table, archaeol and sn -2-hydroxyarchaeol concentration markedly increased at all four sites, again consistent with an anaerobic source, but differed strongly among sites. The differences apparently reflect a combination of vegetation – ericaceous and graminoid plants as opposed to Sphagnum spp. and other mosses lacking root systems – and temperature influence on methanogenesis. In particular, low ether lipid concentrations in Finland probably reflect the lack of vascular vegetation possessing well-developed root systems, together with low mean annual temperature. Similarly low concentrations of archaeol and sn -2-hydroxyarchaeol in a German bog likely result from winter temperatures below 0 °C and a relatively shorter growing season. The occurrence of sn -2-hydroxyarchaeol is limited to a narrow and shallow depth range, indicating that it is poorly preserved, but archaeol persists throughout the cores. Decoupling the concentration of archaeol and the more labile sn -2-hydroxyarchaeol below ca. 50 cm suggests that the former records fossil biomass rather than living biomass. If so, then downcore variation in archaeol concentration likely reflects past changes in methane cycling, and archaeol, pending further developmental research, could serve as a new tool for reconstruction of past peatland biogeochemistry.

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.

Long chain alkenones and photosynthetic pigment derivatives (chlorins) are commonly employed biomarkers in the reconstruction of past sea surface temperatures (SSTs) and organic carbon export from the surface to the deep ocean. For these studies, marine sediment samples are often available which have been air dried or freeze-dried, given that these are common methods for removing water from sediments prior to microfossil analysis. We compared both drying procedures by analysing samples from two sediment cores (ODP 1087, southeast Atlantic and M36/2-MC435, North Atlantic). We found that significant losses of chlorins (>25%) and alkenones (up to 75%) occur with air-drying relative to freeze-drying. Changes in the composition of pigments are also likely. The alkenone unsaturation index U 37 K ′ is sensitive to the drying method, showing an increase of up to 0.02 units relative to freeze-drying. However, this represents a maximum increase in SST estimates of only 0.5 °C. The tests suggest that freeze dried samples, rather than air dried sediments, should preferably be used to determine the sedimentary concentration of biomarkers. However, if chlorins are the main target compounds, wet extraction with acetone of sediment results in ca. 12% higher yield than the extraction of freeze-dried sediments with acetone/water.