Stable isotope and trace element investigation of two contemporaneous annually-laminated stalagmites from northeastern China surrounding the "8.2 ka event"

Abstract

The prominent "8.2 ka event" was well documented in the Greenland ice cores. It remains unclear, however, about its duration, structure and forcing mechanism at low- to mid-latitude regions. Here we use the physical and geochemical data of stalagmites from the Nuanhe Cave in Liaoning Province, northeastern China, to reconstruct a detailed history of East Asian monsoons covering the entire duration of the event. High-resolution chronologies of two contemporaneous stalagmites, each consisting of at least 770 yr annual growth bands, were established by calibrating and anchoring the floating band-counting ages against five high-precision ²³⁰Th dates. Two oxygen isotope profiles replicate each other on annual-decadal timescales despite their difference in growth rates, indicating that the δ¹⁸O variability has a climatic origin largely associated with changes in the rainfall δ¹⁸O from the West Pacific during summer season. A signal from the "8.2ka event" was faint in our δ¹⁸O records, not as significant as Indian monsoon dominated stalagmite δ¹⁸O records from Qunf in Oman and Dongge in Southern China. However, our δ¹³C and Ba/Ca profiles, as indicators of local environmental changes, provide strong support for a climate reversal centred at 8.2 ka BP, which is likely controlled by winter monsoon circulations via the westerly winds associated with North Atlantic climate. Therefore, we concluded that the winter- and summer-Asian monsoons responded independently to the high northern latitude climate.