Abstract
This study deals with the palaeohydrological information obtained from lipids composition and vegetal tissue preservation of two peat cores from Asturias, North Spain. The two profiles differ in the type of peatland (raised bog in La Borbolla and blanket bog in Buelna) and the type of organic matter being more bryophytic in the raised bog and more herbaceous in the blanket bog. The peatlands are located close to the coast on impermeable, old flat erosion surfaces which favoured peat accumulation within a distance of 3.5km from each other. The accumulation rate varied between 0.05 and 0.07mm/yr and the records extend from around 9000 to 2500cal.yrBP.The main differences between the two peat sites can be summarized as follows: the raised bog has lower mineral matter content and H/C atomic ratio and higher C/N ratio and extraction yields compared to the blanket bog. It has also a higher Tissue Preservation Index for Huminite macerals and increasing Inertodetrinite Index with depth. Regarding biomarkers, the raised bog has a relatively higher concentration of n-alkane-2-ones compared to the corresponding n-alkane of similar carbon number, higher concentration of medium- vs. high-molecular-weight-methyl-ketones and higher triterpenoids/steroids ratio than the blanket bog.Alternating humid/dry periods have been recorded in both profiles based on lipid concentrations indicating that the Sphagnum-rich intervals in the raised bog are more sensitive than the herbaceous blanket peat record to climatic variations. The main humid intervals identified are dated as 5000–7500cal.yrBP in the blanket bog and as 6000–3500cal.yrBP and last 2500cal.yrBP in the raised bog and correlate with the humid periods traced in other peatlands locations in this region. The transition Middle-to-Late Holocene is characterized by humid conditions in the region which favoured the Sphagnum growth in the peats.The reflectance of huminite in these records appears to be more related with differences in the oxidative conditions than with variation of peat maturity. It is higher in the layers with high mineral matter content at the beginning of organic matter accumulation and also in the upper part of the profile subjected to seasonal desiccation. A more intense biochemical gelification coincides with higher concentration of hopanoids derived from bacteria in the upper part of the profile (acrotelm).High amount of nonadecan-2-one (K19) and high concentrations of triterpenyl acetates, which are also determined in other peat profiles from Northern Spain are also detected in these profiles. This indicates that the specific conditions required for the formation of these compounds, probably associated to wet temperate climate, dominated throughout the region.
Highlights
Since the early work of Blytt (1876) and Sernander (1909), who established a climatostratigraphic division of the Holocene based on alternating dark peat layers containing wood associated to drier and warmer climate, and lighter-coloured, Sphagnum-rich horizons indicative of wetter cooler conditions, there has been an increasing number of palaeoclimate studies using peat-bog archives (e.g. Blackford, 2000; Charman, 2002; Barber et al, 2003; Bindler, 2006)
The main differences between the two peat sites can be summarized as follows: the raised bog has lower mineral matter content and H/C atomic ratio and higher C/N ratio and extraction yields compared to the blanket bog
La Borbolla profile reaches a depth of 56 cm and consists of around 8 cm of living vegetation dominated by Sphagnum, followed by an interval of bryophytic reddish peat with abundant roots
Summary
Since the early work of Blytt (1876) and Sernander (1909), who established a climatostratigraphic division of the Holocene based on alternating dark peat layers containing wood associated to drier and warmer climate, and lighter-coloured, Sphagnum-rich horizons indicative of wetter cooler conditions, there has been an increasing number of palaeoclimate studies using peat-bog archives (e.g. Blackford, 2000; Charman, 2002; Barber et al, 2003; Bindler, 2006). Any peat deposit can offer palaeoenvironmental information, those with a higher palaeoclimate potential are rain-fed ombrothrophic bogs, the evolution of which is closely linked to meteoric precipitation without any influence from surface water or aquifers (Barber et al, 2003). Both raised bog (van Geel 1978; Barber et al, 1994, Galka et al, 2013) and blanket mire records (Blackford and Chambers, 1991; Chambers et al, 1997; Ellis and Tallis, 2000) have been used for palaeoenvironmental studies. High precipitation sustains the blanket bogs that generally have a lower
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