A multiproxy approach of environmental changes in the last millennia reconstructed from an ombrotrophic peat archive (Frasne mire, France)

Fatima Laggoun-Défarge (1) , Arnaud Huguet (2) , Frédéric Delarue (1) , Vincent E. J. Jassey (3) , Edward A.D. Mitchell (4) , Emilie Gauthier (5) , Claude Le Milbeau (1) , Laurent Grasset (6) , Sylvie Derenne (2) , Sébastien Gogo (1) , Daniel Gilbert (5) , Andre-Jean Francez (7) , Alexandre Buttler (8) , Hervé Richard (5)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 METIS - Milieux Environnementaux, Transferts et Interactions dans les hydrosystèmes et les Sols
3 EPFL - Ecole Polytechnique Fédérale de Lausanne
4 Institute of Biology - Laboratory of Soil Biology
5 LCE - Laboratoire Chrono-environnement (UMR 6249)
6 IC2MP [Poitiers] - Institut de chimie des milieux et matériaux de Poitiers [UMR 7285]
7 ECOBIO - Ecosystèmes, biodiversité, évolution [Rennes]
8 Swiss Federal Institute for Forest, Snow and Landscape Research WSL

Peatlands have stored ca. one-third of the global soil carbon stock because of low rates of plant residue decomposition due to oxygen limitation resulting from waterlogging which inhibits microbial activities. Thus, thanks to the continuous accumulation organic matter (OM), peatlands are suitable archives for the reconstruction of past environmental changes. The combination of natural climatic variations and human impacts (particularly during the late Holocene) represents a challenge for reconstructing past environmental changes from peat archives, and requires the combination of several proxies. Within the PEATWARM project (ANR-07-VUL-010), we investigated a 4 m peat profile collected in a bog located in Frasne mire (French Jura Mountains) and covering the last 7,400 years BP. We analysed peat OM composition (lignin-derived phenolic monomers, monosaccharides, lipids), testate amoebae, branched glycerol dialkyl glycerol tetraethers (GDGTs) and pollen. Major changes in OM sources and environmental conditions were revealed at 2.5 m depth (ca. 5,000 yrs BP). Below 2.5 m depth, higher contents of lignin-derived phenolic monomers were found suggesting a predominance of vascular plants (e.g. sedges). In this deeper section, the peat composition is also characterised by (i) higher percentages of amorphous OM, (ii) lower percentages of mucilage and fungal hyphae, and (iii) lower cellulosic sugar contents and C/N ratio. In addition, at this time (around 5,000 yrs BP), pollen analysis revealed a change in vegetation with especially the disappearance of Pinus. Taken together, these results indicate that a rapid shift of the ecosystem functioning occurred ca. 5,000 years ago from a minerotrophic fen to an ombrotrophic Sphagnum-dominated peatland.

Domaines: Interfaces continentales, environnement

Fatima Laggoun-Défarge, Arnaud Huguet, Frédéric Delarue, Vincent E. J. Jassey, Edward A.D. Mitchell, et al.. A multiproxy approach of environmental changes in the last millennia reconstructed from an ombrotrophic peat archive (Frasne mire, France). 27th International Meeting on Organic Geochemistry, Sep 2015, Prague, Czech Republic. ⟨insu-01291170⟩