Understanding potential consequences of the actual global warming requires mastering past environments evolution linked with anthropic and/or climate variability. High altitude proglacial lakes are key natural archives because they can accurately detect phases of glacial fluctuations and related environmental changes. Lake Blanc Huez (LBH, 2500 m asl) located at 45°N was thus selected because local glaciers extension during the Little Ice Age was restricted to the upper part of its catchment area and because nearby Saint-Sorlin glacier is instrumented since 1957 and considered as representative for the NW Alpine region.
To track palaeoenvironmental evolution and glacial fluctuations, a multiproxy approach is used. It includes seismic profiling (3.5 kHz), piston coring, radionuclide and radiocarbon dating together with a high resolution analysis of clastic and organic sedimentation (laser grain size, magnetic susceptibility, gamma-density, spectrophotometry, major and trace element measurements). Detailed organic analysis (Rock Eval pyrolysis and quantitative organic petrography) are also performed on lacustrine sediments, soils and geological formations in order to document specific organic tracers.
LBH documents the last 9800 yrs. Its upper clastic unit, corresponding to the Neoglacial period, covers the last 5400 yrs and reflects the dominating contribution of fine-grained glacial sediments and the autochthonous algal production (grey amorphous). A progressive transition towards an organic rich basal unit (Total Organic Carbon =5%) essentially made of soils tracers (red amorphous) and pollens suggests reduced glacier activity allowing pedogenesis and development of a vegetation cover in the massif before 5400 yrs cal BP. This bimodal Holocene sedimentation is in addition punctuated by smaller scale fluctuations: a glacier advance at 8200 cal BP during the Early Holocene and glacier retreats during Early Bronze Age, Iron Age, Roman period and Medieval Warm Period.