In this study, to reconstruct the paleoclimatic history, pollen and oxygen isotope were analyzed on the 160 samples of a 2.7 m peat core from Taishizhuang, Huailai County, Hebei Province. Combining our data with other information of climate history and archaeology from this area, we found that there is a close linkage between cultural development and the mid-Holocene (6000-3000 cal. aBP) environment changes. The main results and conclusions are presented as the following: The climate during 5678-5400 cal. aBP was unstable and in general colder and drier than today. From 5400 to 4800 cal. aBP the climate was much warmer and wetter than before. The climate during 4800-4300 cal. aBP was persistently cold, with an exceptional cold event occurring at 4600-4300 cal. aBP. This cold event was recorded at several other localities in Northern China even the Northern Hemisphere and played an important role in the cultural development. After the cold event, there was a return to warmer conditions between 4200 and
JIN Guiyun & LIU Dongsheng (LIU Tungsheng)Institute of Cultural Relics and Archaeology of Shandong Province, Jinan 250012, China
Environmental history of the northern continental shelf of the South China Sea during the last 280 ka BP, e.g. Marine Isotope Stages 1-8 (MIS 1-8) was reconstructed based on poi len record from the top 225m of ODP 1144 Site. During the interglacial periods, pollen assem blages are predominated by pine similar to those of the present day indicating that the environ ment of the interglacial periods was more or less close to that of today. Nevertheless, those from glacial periods are characterized by a large amount of herbaceous pollen, e.g. Artemisia,Gramineae, Cyperaceae, etc. inferring that grassland covered the merged continental shelf when the sea level lowered and the continental shelf was exposed. The exposed areas of the shelf were insignificant before MIS 5, but enlarged since MIS 4 and reached its maximum during MIS 2 ac cording to ratios of pollen percentages between pine and herbs. The history of different exposure of the shelf can be compared with transgression records of the coastal areas of China and might result from neotectonic movement of Chinese continent. Some changes also took place in the components of grassland growing on the shelf during glaciations. Gramineae is the main element at MIS 8. Then Artemisia increased upwards the profile and at last became the main component at the Last Glacial Maximum (MIS 2). Such changes in vegetation might be in response to cooler and drier climate.
Systematic grain-size analysis has found that Chinese loess generally shows bimodal distribution composed of overlapped coarse and fine components. Sedimentary dynamic illustra-tion indicates that the coarse component was mostly the product of low-level monsoonal circulation, and the fine component was mainly transported by high-level circulation dominated by westerly in northern China. Grain-size series of coarse component consistently indicates that the monsoonal circulation strengthened in glacial stages and weakened in interglacial stages over Loess Plateau. The latitude differentiation of fine component series suggests that the westerly circulation intensi-fied and shifted to about 35oN in glacial stages, conversely, weakened and shifted to 37oN in inter-glacial stages. Grain-size variation trends of coarse and fine components revealed by Luochuan loess-paleosol suggest that the contribution of westerly circulation to eolian loess decreased and its intensity weakened in the last 2.6 Ma, which is accompanied by strengthening intensity and increasing contribution of the monsoonal circulation. This variation trend was marked by an abrupt change in the transition period of 1.20.9 Ma, which probably reflected the controlling role of Tibet Plateau uplift on the atmospheric circulation of northern China.
In this paper, we use the automatic orbital tuning method to establishthe time scales of Lingtai and Jingchuan loess-soil section, China, and Chashmanigar loess-soil section, Tadzhikistan, analyse the evolution of the ～100 ka cycles of the three paleoclimate records respectively and afterwards employ the auto-bicoherence method to detect the coupling between the ～100 ka periodicity and periodicities of obliquity, precession and semiprecession. The results show thatfrom 0.0 Ma to 0.8 Ma there exists a quadratic phase coupling between ～100 ka period and the period components of precession(16 ka) and semiprecession(about 13.8 ka, 12.4 ka, 11.1 ka), while from 1.6 Ma to 2.6 Ma, between 128 ka period and the period components of precession(19.3 ka and 16.8 ka) and semiprecession (about 10 ka). Evidence from the above calculation suggests that nonlinear interaction between precession and semiprecession waves may be the cause to produce ～100 ka cyclicity in loess records.
One active stalagmite from the Water Cave in Liaoning Province contains growth layers of three sizes. Based on thermal ionization mass spectrometry 230Th dating, we found that middle size layers are annual layers, with each middle layer consisting of one narrow dark layer and a wide bright layer. The small layers within middle layers are sub-annual layers and the large layers are multi-year layers. Based on the layer-counting method, we established a high-resolution time scale for layer thickness. Our results reveal two dramatic century-scale climate cycles over the past 1000 years in this region.
