Paleohydrological history of Lake Allos (2200 m a.s.l) since 13 500 cal a bp in the Mediterranean Alps inferred from an ostracod δ 18 O record

This paper presents the first Lateglacial/Holocene (the last 13 500 cal a bp ) ostracod δ 18 O record to infer hydroclimate variability in the Southern French Alps. Cytherissa lacustris (δ 18 O sp ) shells extracted from the sediments of Lake Allos allowed a reconstruction of δ 18 O lake water (δ 18 O lw ) except for the interval 5800–2800 cal a bp. The shape of the Younger Dryas (YD) clearly differed from records documented in the northern Alps. First, δ 18 O lw values remained close to modern values before a marked drop ca. 12 000 cal a bp. Then, after several oscillations, δ 18 O lw values increased, reaching the highest value of the record ca. 6100 cal a bp during a thermal optimum for this latitude. Finally, low δ 18 O lw values occurred from 450 to 100 cal a bp during the Little Ice Age (LIA) following the Medieval Climate anomaly. At the beginning of the YD, δ 18 O lw probably reflected changes in local glacier dynamics and precipitation sources. The following decrease in δ 18 O lw values was associated with higher freshwater inputs during the second half of the YD. During the LIA, the low δ 18 O values are consistent with a higher torrential activity and lower air temperatures.