Chronological constraints on the Holocene glacier dynamics of the Argentière Glacier (Mont Blanc massif, France) based on cosmogenic nuclide dating

Abstract : While reconstruction of glacier fluctuations during the Holocene provides important information about the glacier response to natural climate change, it is still a challenge to accurately constrain chronologies of past glacieradvances and retreats. Moraine deposits and roches moutonnées represent valuable geomorphic markers ofadvanced glacier extensions, while the currently ongoing glacier melt uncovers proglacial bedrock that can beused as a new archive to investigate the durations when a glacier was in retreated position during the Holocene.Our study focuses on the Mont-Blanc massif (MBM), located in the Western Alps and hosting some of the largestglaciers of Europe. Chronologies of Holocene glacier fluctuations in this area are still sparse, even if recentstudies considerably improved the temporal reconstruction of Holocene advances of some glaciers in the MBMand locations near-by (e.g. Le Roy et al., 2015). Here we present preliminary 10Be exposure ages obtained frommoraine boulders, roches moutonnées and pro- and subglacial bedrock in the area of the Argentière Glacier,located on the north-western flank of the MBM. The ages of moraine boulders and roche moutonnée surfacesoutboard of the investigated moraines suggest that the Early Holocene deglaciation of this area started around11 ka ago. Also, 10Be measurements of recently deglaciated bedrock surfaces indicate that the glacier was ata position at least as retracted as today for a minimum duration of 7 ka throughout the Holocene. The 10Bemeasurement of one sample from a surface that is currently still covered by 60 m of ice suggests that the glacierwas shorter than today for at least a duration of 3 ka.These first results will soon be completed with in situ 14C measurements, which will allow us to quantify and takeinto account subglacial erosion rates and thus to more accurately determine the cumulative duration of pro- andsubglacial bedrock exposure during the Holocene