A Southern Alps and Northern Pyrenees Holocene record of snowmelt-induced flood events and clastic layers associated with negative NAO phases inWestern Europe

• Main Authors: Simonneau, Anaëlle, Chapron, Emmanuel, Galop, Didier
• Other Authors: Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Géographie de l'environnement (GEODE), Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS), Geophysical Research Abstracts, ANR-11-LABX-0010,DRIIHM / IRDHEI,Dispositif de recherche interdisciplinaire sur les Interactions Hommes-Milieux(2011)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2014
• Subjects: [SDE.ES]Environmental Sciences/Environment and Society; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; North Atlantic; North Atlantic oscillation
• Online Access: https://hal.science/hal-01790135

International audience The origin of both extreme flood events in Lake Ledro (southern Italian Alps) and coarse sandy layers in twodisconnected lakes from the Bassies valley (Lakes Majeur and Sigriou, northern Pyrenees) have been relatedto the impact of snowmelt processes enhancing erosion of mountainous drainage basins (1, 2) throughout theHolocene. Because of increasing human impact on catchment erosion processes since the mid-Holocene in thesewestern European mountain ranges, this study compares these well-dated lacustrine sequences in order to furtherdocument the influence of westerlies and of the North Atlantic Oscillation on clastic supply in contrasted lakebasins. The integrative approaches performed on each site allow us to show that organic and minerogenic markers,such as non-pollen microsfossils, Rock-Eval pyrolysis or X-ray microfluorescence, are powerful tools to identifyclastic sediment source areas. At Ledro, we therefore demonstrated that over the Late Holocene snowmelt-inducedflood events essentially remobilized high altitude pasture areas whereas afterwards the flood events affectedformer forested areas from lower altitude1. In the Pyrenees, the southern slopes of lakes Majeur and Sigriouare characterized by two narrow canyons whose drainage basins are disconnected, relatively small and limitedto the high altitude part of the valley of Bassiès. Our results demonstrated that the mid–late Holocene periodwas regularly interrupted by coarse sandy layers affecting both lakes Majeur and Sigriou and reflecting the highsensitivity of the two active canyons to intense rainfall or snowmelt periods2. While extreme flood deposits inLake Ledro during the Bronze Age period may result from the combination of both climate and human activities,contemporaneous extreme flood events in Ledro and coarse sandy layers in the Bassiès lakes, dated to AD 1710,AD1530, AD1360, AD940, AD570 and 1850, 1050, 1410, 1850, 2690, 4190, 4800 cal BP, testify of regionalhydrological events synchronous with European climatic ...