Shrinkage of East Asia Winter Monsoon Associated With Increased ENSO Events Since the Mid-Holocene

Instrumental records indicate a close relationship between the El Nino-Southern Oscillation and the East Asian winter monsoon (EAWM) on interannual to decadal time scales. However, few studies have examined possible links between them on centennial/millennial time scales. In Northeast China, modern observations show that the immigration of temperate forest trees such as Pinus (pine) and Quercus (oak) into cold temperate boreal forest is sensitive to changes in winter temperature. Here we present a continuous high-resolution pollen record from Lake Moon in the central part of the Great Khingan Mountain Range, Northeast China. The record reveals increasing contents of Pinus and Quercus pollen after similar to 6.0 ka cal. BP, which may indicate a gradual weakening of the EAWM. It is broadly coupled with an increasing El Nino frequency since the middle Holocene, and we observe a statistically significant correlation between the percentages of Pinus and Quercus and a time series of El Nino events. On the centennial to millennial time scale, the results of wavelet analysis and band-pass filtering show that the occurrence and development of El Nino have also promoted a weaker EAWM after similar to 6.0 ka cal. BP, which is inversely correlated with the variation of the ca. 500-year cycle originated from changes in solar output. These results imply that the climate transition in the mid-Holocene is caused by the change of variations in solar activity and amplified by ocean circulation El Nino-Southern Oscillation to influence the East Asian Monsoon system, especially the EAWM, and finally change the vegetation in Great Khingan Mountain Range.