Recent climatic and anthropogenic imprints on lacustrine systems in the Pyrenean Mountains inferred from minerogenic and organic clastic supply (Vicdessos valley, Pyrenees, France)

Anaëlle Simonneau (1, 2) , Emmanuel Chapron (1) , Thierry Courp (3) , K. Tachikawa (4) , Gaël Le Roux (5) , Sandrine Baron (6) , Didier Galop (2) , Marta Garcia (4) , Christian Di Giovanni (1) , Mikael Motelica-Heino (1) , Florence Mazier (2) , Anthony Foucher (7) , Thomas Houet (2) , Marc Desmet (7) , Edouard Bard (4)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 GEODE - Géographie de l'environnement
3 CEFREM - Centre de formation et de recherche sur l'environnement marin
4 Collège de France - Chaire Evolution du climat et de l'océan
5 LEFE - Laboratoire Ecologie Fonctionnelle et Environnement
6 TRACES - Travaux et recherches archéologiques sur les cultures, les espaces et les sociétés
7 GéHCO EA6293 - GéoHydrosystèmes COntinentaux

High-resolution seismic profiling has been combined with geochemical analyses of both watershed samples and five lacustrine cores retrieved from two natural lacustrine basins of glacial origin: Lake Majeur and Lake Sigriou (1630 m a.s.l. and 1995 m a.s.l., respectively, Eastern French Pyrenees). Identifying specific minerogenic and organic markers of autochthonous and allochthonous supply, data allow documenting past climatic and anthropogenic pressures. Over the past century, the lacustrine sediment of Lake Majeur has been essentially composed of algae, drastically contrasting with the natural sedimentary infill of the basin, mainly resulting from soil erosion from the mid-late Holocene. Since ad 1907, the Lake Majeur has been used for hydroelectricity production. Human-induced lake-level regulations, affecting up to 37% of the lacustrine surface, have increased by fourfold the accumulation rate of the lake and favoured water enrichment. Rubidium abundance within the lacustrine sediments of the two lakes reflects the mid-late Holocene palaeohydrology. After dam construction in ad 1907, greater quantities of rubidium found in Lake Majeur sedimentary infills indicate drier climatic periods, such as from ad 1975 to ad 1982, during which water reservoirs were particularly in demand. Inversely, before the dam was built, rubidium fluctuations were correlated with wetter conditions and hydrological events were recorded as sandy layers deposited by canyon reactivation, synchronous with European climatic deterioration phases. We notably document that the Mediaeval Climate Anomaly was interrupted by some humid periods dated c. ad 940, ad 1080, ad 1100 and ad 1250. We also date the onset of the 'Little Ice Age' c. ad 1360 and identify that this period was wetter after c. ad 1500.

Keywords: Trophic state; hydropower; lake sediment; soil erosion; Pyrenees; mid-late Holocene

Domains: Earth Sciences; Environmental and Society; Global Changes

Anaëlle Simonneau, Emmanuel Chapron, Thierry Courp, K. Tachikawa, Gaël Le Roux, et al.. Recent climatic and anthropogenic imprints on lacustrine systems in the Pyrenean Mountains inferred from minerogenic and organic clastic supply (Vicdessos valley, Pyrenees, France). The Holocene, 2013, pp.1764-1777. ⟨10.1177/0959683613505340⟩. ⟨insu-00907274⟩