Through the use of reliable AMS dating of high resolution (15-30 years) peat and the establishment of monsoon climate proxies sequence, we have been able to recognize several cold, dry events in the Tibetan Plateau during the Holocene. The more obvious ones occurred around 12800, 11300, 10200, 9580, 8900, 6400, 4400, 3700, 2800 and 1500 cal. aBP. These events correlate well with both ice rafting events recorded in high latitude North Atlantic Ocean sediment cores and cooling events in the low latitude SST. Spectral analysis indicates high frequency climate variation on centennial-millennial time scale during the Holocene. This further reflects Holocene climate instability and the existence of centennial-millenium scale rhythm in mid latitude areas as well.
Correlation function analysis shows that total precipitation from April to early July (to July 10) in growing season limits the ring width of Picea Koraiensis significantly in Baiyinaobao, Xilinhot, Inner Mongolia. Thus a transfer function is designed to reconstruct the total precipitation from April to early July over the region for the last 160 years. The explained variance of the reconstruction is 49.3% (and 45.7% when adjusted for loss of degrees of freedom, N = 31, r = 0.702, F = 13.608, p < 0.0001). There are three relatively wet periods in the reconstruction which are: 1869—1875, 18861921 and 19431968, and four relatively dry periods: 1851—1868, 1876—1885, 1922—1943 and 1969—1999. Among them, the wet periods of 1886—1921 and 1943—1968, and the dry period of 1922—1943 appeared almost at the same time with those in Mt. Qilian region. Meanwhile, the dry period of 1922—1943 corresponds to high temperature and low rainfall during the 1920s and thereafter, and wetness of 1943—1968 corresponds very well to low temperature and more precipitation after the 1940s in Northwest, Northern China and the Changjiang River drainage basin. Calculation shows that the reconstruction series is significantly correlated with local dry-wet index (r = -0.234, p < 0.007, N = 143). Wavelet analysis indicates that there is a 22-a cycle in the precipitation of April to early July during 18381920, and an 11-a cycle during 1920—1952. No more cycles that reach 95% confidence limits are identified after 1953. The precipitation from April to early July quickly dropped into low during the 1920s. After 1950, precipitation shows a declining trend, but the reconstruction shows a tendency of increase in the late of 1990s.
Three tree-ring rainfall reconstructions from China and Korea are used in this paper to investigate the East Asian summer monsoon-related precipitation variation over the past 160 years. Statistically, there is no linear correlation on a year-by-year basis between Chinese and Korean monsoon rainfall, but region-wide synchronous variation on a decadal-scale was observed. More rainfall intervals were 1860-1890, 1910-1925, and 1940-1960, and dry or even drought peri-ods were 1890-1910, 1925-1940, and 1960-present. Reconstructions also display that the East Asian summer monsoon precipitation suddenly changed from more into less around mid-1920. These tree-ring precipitation records were also confirmed by Chinese historical dry-ness/wetness index and Korean historical rain gauge data.
