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

Abstract

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.

Summer paleohydrology during the Late Glacial and Early Holocene based on δ2H and δ18O from Bichlersee, Bavaria

“…Ammersee, for instance, located 80 km northwest of Bichlersee near Munich, has a large catchment area and a large and deep water body. δ 18 O on benthic ostracods from Ammersee thus likely represents an annual lake water signal 17 and is less sensitive to the effect of evaporative enrichment 14 . Bichlersee and its catchment, on the other hand, are very small and particularly sensitive to record the isotopic signal of summer precipitation.…”

“…The Late Glacial comprises the warm Bølling–Allerød interstadial (starting ~ 14.7 ka BP) and the cold Younger Dryas stadial (from ~ 12.8 to 11.7 ka BP) 11 , 12 . Paleoclimate information from the Alps during that time is inferred inter alia from stable oxygen isotope records (δ 18 O) derived from lake sediments 13 – 17 and speleothems 18 , 19 . Those δ 18 O records mostly resemble the δ 18 O records from Greenland ice cores 20 and are often interpreted to document past temperature changes.…”