Stable isotope and trace element investigation of two contemporaneous annually-laminated stalagmites from northeastern China surrounding the "8.2 ka event"
1College of Geography Science, Nanjing Normal University, Nanjing, 210097, China
2Institute of Global Environment Change, Xi'an Jiaotong University, Xi'an, 710049, China
3Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota, 55455, USA
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 throughout the event. Two contemporaneous stalagmites were annually counted for at least 770 yr anchored by five 230Th dates to establish an inter-calibrated high-resolution timescale. Two oxygen isotope profiles replicate each other at annual-decadal timescales although their counted growth rates are not consistent, 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 "8.2 ka 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 a strong support for a deteriorated climate episode centred at 8.2 ka BP, likely controlled by winter monsoon circulations via the westerly winds associated with North Atlantic climates. Therefore, we concluded that the winter- and summer-Asian monsoons responded independently to the high northern latitude climates.