Paleohydrological history of Lake Allos (2200 m a.s.l) since 13 500 cal a bp in the Mediterranean Alps inferred from an ostracod δ18O record

This paper presents the first Lateglacial/Holocene (the last 13 500 cal a bp) ostracod delta O-18 record to infer hydroclimate variability in the Southern French Alps. Cytherissa lacustris (delta O-18(sp)) shells extracted from the sediments of Lake Allos allowed a reconstruction of delta O-18(lake water) (delta O-18(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, delta O-18(lw) values remained close to modern values before a marked drop ca. 12 000 cal a bp. Then, after several oscillations, delta O-18(lw) values increased, reaching the highest value of the record ca. 6100 cal a bp during a thermal optimum for this latitude. Finally, low delta O-18(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, delta O-18(lw) probably reflected changes in local glacier dynamics and precipitation sources. The following decrease in delta O-18(lw) values was associated with higher freshwater inputs during the second half of the YD. During the LIA, the low delta O-18 values are consistent with a higher torrential activity and lower air temperatures.

Automated summary

This study presents the first record of ostracod delta O-18 from the Late Glacial/Holocene period in the Southern French Alps, and infers hydroclimate variability. The results show that during the Younger Dryas, the lake water oxygen isotope values reached their highest point, while during the Little Ice Age, they were lower.