Based on the analysis of carbonate content and loss on ignition for a long sediment core (737 m in length) drilled in Heqing, the orbital scale evolution of the Southwest Monsoon is revealed, by using overlapped spectral analysis and filter methods. It is shown that the obliquity cycle and precession cycle are the key factors for the Southwest Monsoon evolution and that the change of the global ice volume and the uplift of the Qinghai-Tibetan Plateau also impose great influences on it.
Multifold palynological diversity indices calculated by pollen data of the Heqing deep drilling core are synthetically analyzed, the results show that the plant diversity rapidly increased and its fluctuant amplitude and frequency evidently largened during the stages of 2.729―2.608 Ma, 1.176―0.342 Ma and since 0.118 Ma respectively, while during the other periods the plant diversity was relatively low with a gentle fluctuation. To discuss further the relation between ancient plant diversity and paleoenvironment, it is considered that the plant diversity in the Heqing region lies on increase or decrease of vertical vegetational belts in mountains around the studied area and richness of components of these vegetational belts, and is controlled by amplitude of tectonic uplift of mountains and climatic changes. The high plant diversity during 2.729―2.608 Ma responded to the strong uplift of mountains at the stage, while the plant diversity greatly increased and its fluctuant amplitude and frequency markedly largened at about 1.176 Ma was obviously response to the Middle Pleistocene Transition. The plant diversity and its fluctuant amplitude and frequency increased further at about 0.991 Ma may be superposably affected by both the Middle Pleistocene Transition and the tectonic uplift. The plant diversity increased since 0.118 Ma may indicate that the southwest monsoon strengthened and humid climate more fitted many kinds of plants to grow.
The evidence of human activities around Erhai Lake catchment was revealed by pollen records from a sedi- ment core in the lake, northwest Yunnan Province. The 14 chronologic sequence based on AMS C data made it possi- ble for pollen results to compare with archaeological records and historical documents. The preliminary deforestation started from the selective clearance at about 5500 C a BP, 14 marked by the loss of vertically distributed montane forest and the expansion of second pine woodland across the catchment. The deforestation resulted in the increase of sur- face runoff and the enhanced erosion in the catchment. The increased herbs of pasture and crop suggested the primitive agriculture and stockbreeding in study region. With the lim- ited human activity, as well as the suitable climatic condition, second pine forest expanded quickly, resulting in the weak- ened soil erosion around the basin. The strong forest clear- ance inferred from pollen occurred since 2160 C a BP, par- 14 alleling to the first dense immigration of population, when Yeyu County was first set up around west coast of Erhai Lake, documented in historic record. The development of agriculture led to the steady enhancement of soil erosion from farming land, increasing the input of fine materials and nutrients to the lake. Moreover, the serious deforestation by human activity stressed the vulnerability in ecosystem of the landscape. The time of primary anthropologic impact re- corded from pollen is earlier than that of the oldest archaeo- logical record by 1500 a (14C year).
