Three well-dated Sabina Przewalskii ring-width chronologies from Dulan, China, have been used to reconstruct annual precipitation (from prior July to current June) variations on the northeast Tibetan Plateau since 850 AD. The reconstructions account of the instrumentally recorded precipitation variance are: 54.7% for the period of 1385-2000AD; 50.5% for 1099-1384AD and 45.7% for 850-1098AD. On the millenary scale, the precipitation variation over this region displays “W” shape, which has three peaks and two valleys. The precipitation is low during 1571-1879 AD, and high during 1880-2000 AD. 1900-2000 AD is the century with the highest precipitation over the northeast Tibetan Plateau in the last 1000 years, and 1962-2000 is the period with the highest pre- cipitation, and the highest variability of precipitation as well in the last 1000 years. The reconstructed series also reveals that the variability of annual precipitation is large when the precipitation is more, and contrarily, variability is small when the precipitation is low. With the temperature increasing obvi- ously in the 20th century, the precipitation in the study region significantly increased too, the variability of precipitation became larger, and drought and flooding occurred more frequently. The yearly tree-ring width (high frequency signal) series in this region reflects the local annually precipitation variation. However, the series with 40-year moving average (low frequency signal) cor- responds to the Northern Hemisphere temperature variations on the decadal to centurial scale. It correlates significantly with seven temperature curves of the Northern Hemisphere in the different time spans. For example, the correlation coefficients with the most temperature curves are around 0.9 during the period of 1852-1982 AD. In general, the temperature and the precipitation change syn- chronously in the Dulan region. It means that low temperature corresponds to low precipitation, andvice versa. This relationship may indicate that the climatic pattern i
The variations of summer and winter monsoons during the Holocene in theeastern Tibetan Plateau are shown to follow two basic models based on the reliable dating andhigh-resolution monsoon proxies determinations, one being a synchronous model in that both summerand winter monsoons are strengthening or decreasing, and the other to form a complementary pattern.These two different patterns evenly interact with each other on different time scales and togethercompose a complicated monsoon climatic model in this region. The climatic condition integrated bywinter and summer monsoons is synchronous to the global pattern, which also shows the instability ofthe Holocene climate on centennial-millennial timescale. The abrupt monsoon event in about 6.2 kacat. BP is much more severe than that in ca. 8.0 ka cal. BP, which indicates the regional characterof the Asian monsoon and that the Asian monsoon climate is indeed a window on the global climatesystem.
The "mean value concept" in a mono-linear regression of multi-variables is clarified.Its applications to reconstruction of the past 90-year salinity of the sea surface water in Xisha Islands and to tracing the past 80 ka paleo-geomagnetic events from the Luochuan loess 10Be record are introduced in detail,which show the significance and the potential of the "mean value concept" in geoscience research.
