6,700-year sedimentary record of climatic and anthropic signals in Lake Aydat (French Massif Central)

A 19-meters-long sedimentary record that was retrieved in Lake Aydat (French Massif Central) covers the last 6700 yrs at a high-resolution. A multi-proxy approach (density, magnetic susceptibility, XRF, Rock-Eval analyses, pollen and non-pollen palynomorphs analyses and historical archives study) was used to characterise and tentatively propose a model of the sedimentation. The important deposition rate results from the narrow and incised fluvial valley dammed by a lava flow ca. 8550 years ago. Two contrasted periods of sedimentation (6700±200 - 3180±90 cal. BP, and 1770±60 cal. BP- now) are characterized. The lower unit (mid-Holocene) displays a fine and regular lamination and holds a single, major, flood deposit. This unit is capped by an erosive mass wasting deposit triggered ca. 1770±60 cal. BP. The upper unit (late-Holocene) is made of organic rich and fine grained faintly laminated sediment, with numerous interbedded flood deposits (56 events) and layers resulting from blooms of diatoms. The sedimentation was principally controlled by climatic forcings (solar activity) until ca. 1100 cal. BP, accompanied by detritic events linked to human activities around the lake. Then, a more detrital input attested by numerous and recurrent flood deposits can be linked to the intensification of a persistent anthropogenic impact on the catchment. Two phases of lake eutrophication are highlighted: a first phase between 1200-1130 cal. BP, as a result of increased anthropogenic pressure, and the current phase that could have started ca. 150 cal. BP.