Stalagmite-inferred hydroclimate changes in northern Italy during Allerød/Younger Dryas transition

Description

The Younger Dryas (YD), a 1200-year-long cooling event interrupting the warm Bølling-Allerød period, started from 12,870 ± 30 yr BP (2σ, before 1950 C.E.). Here we present decadal-resolved stalagmite BA18-2 multi-proxy records from Bàsura cave, northern Italy. The StalAge age-depth model with 8 U-Th dates with 2-sigma errors of ± 26-193 yrs shows that BA18-2 encompasses Allerød/YD transition, from 14,038 ± 92 to 12,090 ± 54 yr BP. Oxygen isotope data fluctuate between-7.16‰ and-3.68‰, with a clear 2.4‰ increase during the YD onset at 12,870 ± 30 yr BP. Stalagmite BA18-2 Sr/Ca and Ba/Ca linger from 0.060-0.085 mmol/mol and 6.4-9.1 µmol/mol, respectively, from 14,038 ± 92 to 12,681 ± 55 yr BP, ~2 centuries after the beginning of YD. A clear 160 year-long two-step increase in both Sr/Ca and Ba/Ca records started from 12,681 ± 55 yr BP, which is a 200-yr lag relative to the timing of BA18-2 oxygen isotope increasing trend. We argue that the oxygen isotope could be governed by moisture source; while, the carbon isotopes, Sr/Ca and Ba/Ca ratios predominantly reflect precipitation change. Our results suggest asynchronous thermal and hydrological changes in northern Italy during the Allerøod/YD transition.

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