Abstract
Comeya peatland is located in Picos de Europa National Park (N. Spain) at 851m above sea level, representing the continuous postglacial infill of a hollow (growth rate=0.4mm/yr) during the last 15,000cal.yrBP. Three intervals can be distinguished in the profile: the bottom one, with ash content close to 90%, which is previous to the peatland installation in the area and is followed by an interval with oscillating ash content (30–60%) probably related to alluvial fan sedimentation. The uppermost one corresponds to the peat deposit with ash content generally close to 10%. The present day vegetation consists of Sphagnum species with herbaceous plants and heathers. The study comprises the analysis of some biomarkers with potential as palaeoenvironmental proxies quantified by gas chromatography/mass spectrometry, supported by bulk δ13C and δ15N isotopic. The biomarker assemblage is dominated by the n-alkanes and methyl-ketones with medium-to-high molecular weight and odd number of carbons. The biomarker ratios indicate an enrichment in Sphagnum characteristic compounds at 120–250cm (3150–6350cal.yrBP) reflecting more humid conditions. This episode coincides with higher C/N atomic ratio, higher values of δ13C and lower of δ15N. The wetter conditions of this interval are also shown by the depleted δD values of the n-alkane, particularly those related with mosses as (n-C23 and n-C25) and the enriched δ13C values of both n-alkanes and methyl-ketones.Segregation of δ13C values has been observed for homologues series in Comeya peat with medium molecular weight n-alkanes typical of mosses living in waterlogged environments, being enriched in δ13C values compared with higher molecular weight n-alkanes typical of woody and herbaceous plants of drier habitats. This study has shown a slight enrichment of δ13C values of methyl-ketones compared to n-alkanes, the differences being not conclusive to support a common or different origin for both compound classes.
Highlights
The high preservation rate of organic matter in peatlands and the association of the type of vegetation with the climate conditions linked to the palaeohydrological conditions make peat records appropriate for its use as palaeoarchives (Barber, 1993)
The present study provides further inside into the isotopic composition of n-alkanes and methyl-ketones in the Comeya peat profile allowing to follow the isotopic fractionation in relation to the compound chain length and to the depth of the profile
The uncertainty is greater in the interval between 322 and 580 where a large scatter of values is obtained. This interval corresponds to a great variation in ash contents indicating significant input of allocthonous material to the hollow infill
Summary
The high preservation rate of organic matter in peatlands and the association of the type of vegetation with the climate conditions linked to the palaeohydrological conditions make peat records appropriate for its use as palaeoarchives (Barber, 1993). The organic geochemistry of the peats in this area have received significant attention in recent years showing alternating humid and dry periods (Ortiz et al, 2010; López-Dias et al, 2013b) strong influence of the local hydrology (Ortiz et al, 2016) and the abundance of some specific compounds such as medium molecular weight n-methylketones (Ortiz et al, 2011; López-Dias et al, 2013a; López-Dias et al, 2010a and 2010b; Schellekens et al, 2015) for which the origin is still controversial Among these studies, only that of López-Dias et al (2013a) on Roñanzas peat contains values for 13C composition of n-alkanes and n-methylketones. The present study provides further inside into the isotopic composition of n-alkanes and methyl-ketones in the Comeya peat profile allowing to follow the isotopic fractionation in relation to the compound chain length and to the depth of the profile
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