Biomarkers and inorganic proxies in the paleoenvironmental reconstruction of mires: The importance of landscape in Las Conchas (Asturias, Northern Spain)

Abstract

A B S T R A C TWe determined the lipid distributions (n-alkanes, n-alkan-2-ones, n-alkanoic acids), total organic carbon (TOC), total nitrogen (TN), CajMg and ash content in Las Conchas mire, a 3.2 m deep bryophytedominated mire in Northern Spain covering 8000 cal yr BP. Bog conditions developed in the bottom 20 cm of the profile, and good preservation of organic matter (OM) was inferred from n-alkanoic acid distribution, with the exception of the uppermost 20 cm (last ca. 200 yr). Microbial synthesis of long chain saturated fatty acids from primary OM likely produced a dominance of short chain n-alkanoic acids with a bimodal distribution, as well as the lack of correspondence between the n-alkane and n-alkanoic acid profiles in the upper 20 cm. This was accompanied by an increase in ash content, a decrease in TOC and variation in n-alkane ratio s, thereby suggesting significant changes in the mire, namely drainage and transformation to a meadow, in the last ca. 200 yr. The distribution of n-alkan-2-ones indicated an increase in bacterial source from the bottom of the record to 94 cm, whereas their distribution in the upper part could be attributed mainly to plant input andjor the microbial oxidation of n-alkanes. The different n-alkane proxies showed variations, which we interpreted in terms of changes in vegetation (Sphagnum vs. non-Sphagnum dominated phases) during the last 8000 cal yr BP. C 23 was the most abundant homolog throughout most ofthe record, thereby suggesting dominant humid conditions alternating with short drier phases. However, such humid conditions were not linked to paleoclimatic variation but rather to geomorphological characteristics: Las Conchas mire, at the base of the Cuera Range, receives continuous runoff-even during drier periods-which is not necessarily accompanied by additional mineral input to peat, producing the development of Sphagnum moss typical of waterlogged ecotopes and damp habitats. Thus, although geochemical proxies indicated an ombrotrophic regime in the mire, geomorphological characteristics may make a considerable contribution to environmental conditions.

Organic geochemical evidence of postglacial paleoenvironmental evolution of the Comeya peatland (Asturias, N Spain)

“…As this region is in contact with a warmer and drier Mediterranean climate region, the variation reflected in the peat records would not only be a consequence of the variation of the climate in the Atlantic region, but also of any migration between regions. 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 and2010b;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  13 C composition of n-alkanes and n-methylketones.…”

Maceral composition and molecular markers of two condensed Middle Holocene peat profiles in N Spain

“…yr BP the C/N atomic ratios in both profiles were close to each other, though slightly higher in La Borbolla raised bog. The values are typical for ombrotrophic bogs in the region 13/36 (Pontevedra-Pombal et al, 2006Ortiz et al, 2010Ortiz et al, , 2016Lopez-Dias et al, 2013). The H/C atomic ratio reflects differences in the nature of the organic matter accumulated.…”

“…These have been described in mountainous and littoral locations throughout the Cantabrian region (Fernandez Prieto et al, 1987, Pontevedra-Pombal et al 2006. Organic geochemical studies on Asturian peats have increased in recent years (Ortiz et al, 2010(Ortiz et al, , 2016López-Días et al, 2010aand 2010b, 2013a, 2013b. This work presents an integrated biomarker and petrographic study of two peat profiles which cover the middle Holocene and the transition to the Late Holocene in the oriental part of Asturias.…”

“…The K 19 methyl-ketone increases towards the bottom, a characteristic that has also been observed in a Swedish peat bog (Lehtonen and Ketola, 1990). This was not the case in Roñanzas or Las Conchas profiles, located only a few km away, where high concentrations of K 19 extended throughout the whole three-meter profiles (Ortiz et al, 2010(Ortiz et al, , 2016López-Días et al, 2013a). Methyl-ketones in bogs from North Spain have been recently attributed to a microbial source on the basis of the isotopic values, most probably associated with Sphagnum rich in n-C 25 (López-Días et al, 2013a).…”

Nanoplâncton calcário e a dinâmica oceanográfica no oeste do Atlântico Sul nos últimos 200.000 anos

“…A concentração de carbono orgânico total é um proxy importante que indica o conteúdo de matéria orgânica dos sedimentos (Meyers, 2003;Ortiz, et al, 2016…”