Quasi-cyclic Dry Events in Northeast Asia since the Mid-holocene

Abstract:

Orbital timescale East Asian monsoonal intensity throughout the Holocene shows a first order decreasing trend in the subtropical southeastern Asian sector. This long-term trend is also extended to a variety of paleoclimate records from various regions of the globe. But, the shorter-term paleoclimatic episodes such as millennial-timescale events are in a much debate for their regional presences and periodities. Here we report a stalagmite δ¹⁸O record from Baek-ryong Cave in the central Korean Peninsula that shows the changes in East Asian monsoon intensity since the last 5,000 years. The general pattern of the stalagmite δ¹⁸O record can be divided into 3 orders changes. Most long-term variation in the δ¹⁸O record is orbital scale increasing trend from the bottom to the top of the stalagmite sample with about 0.8 ‰ differences between maximum and minimum δ¹⁸O values. Middle-term variations are most apparent and show about 1,000 years-scale quasi-cyclic variations with about 0.6~1.0 ‰ changes, and lastly, short-term variations are multi-decadal scale fluctuations with about 0.20 ‰ changes. The middle-term cyclic variations are very obvious based on the separation from the range of standard deviation. The variations also display a similarity with many of stalagmite δ¹⁸O records from subtropical Chinese regions in their overall trends and prominent millennial-scale cold/dry events since mid-Holocene. These results indicate that the δ¹⁸O record was controlled mainly by the changes in East Asian monsoon intensity possibly with minor contribution of atmospheric temperature effect. We interpreted that these millennial-scale variations in East Asian monsoon have been affected by changes in solar forcing and North Atlantic overturning circulations. Also, we suggest that 1,000 years quasi-cyclic dry events were at least regional episodes since the mid-Holocene.