ALBERT

Description: Abstract Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source‐to‐sink studies and paleoclimate reconstructions. The Argentera‐Mercantour massif being located at the transition between the Alps and the Mediterranean Sea, its deglaciation chronology can be compared to the sediment budget of the Var River basin. Based on 13 new Cosmic‐Ray Exposure (CRE) 10Be dating performed on moraines and polished crystalline bedrocks and 22 reassessed 10Be CRE ages from similar altitude nearby steep basement surfaces, and from a lake sediment core, we constrain the deglaciation chronology of the Argentera‐Mercantour massif. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif in agreement with a major glacier recession at ca. 15 ka, at the onset of Bølling transition between the Oldest and Older Dryas. Main deglaciation of the upper slopes (2,700‐2,800 m a.s.l.) occurred after the LGM at 20.8‐18.6 ka, followed by the main deglaciation of the lower slopes (2,300 m a.s.l.) at 15.3‐14.2 ka. Finally, the flat polished surfaces above 2,600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re‐advance stage between 12 and 8‐9 ka. At lower elevations, the Vens Lake located at 2,300 m a.s.l., allows evidencing the onset of lake sedimentation at ca. 14 ka and a transition towards a vegetated environment that mainly occurred before 8 ka. Moraine final stabilization at 5 ka might reflect denudation acceleration during the Holocene humid phase. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after ca. 15 ka. This major deglaciation is correlated with a 2.5 fold decrease of sediment discharge of rivers into the Mediterranean Sea.