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 ¹⁸O record

ABSTRACT

This paper presents the first Lateglacial/Holocene (the last 13 500 cal a bp) ostracod δ ¹⁸O record to infer hydroclimate variability in the Southern French Alps. Cytherissa lacustris (δ ¹⁸O _sp) shells extracted from the sediments of Lake Allos allowed a reconstruction of δ ¹⁸O _{lake water} (δ ¹⁸O _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 ¹⁸O _lw values remained close to modern values before a marked drop ca. 12 000 cal a bp. Then, after several oscillations, δ ¹⁸O _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 ¹⁸O _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 ¹⁸O _lw probably reflected changes in local glacier dynamics and precipitation sources. The following decrease in δ ¹⁸O _lw values was associated with higher freshwater inputs during the second half of the YD. During the LIA, the low δ ¹⁸O values are consistent with a higher torrential activity and lower air temperatures.