末次间冰期以来青藏高原东部季风演化的黄土沉积记录

对青藏高原东部甘孜地区末次间冰期以来黄土地层的磁化率、粒度、CaCO₃含量和有机碳含量等气候代用指标的综合分析表明,末次间冰期以来青藏高原东部冬、夏季风分别经历了5次和6次较为强大的时期；其演化阶段基本可与深海氧同位素曲线(SPECMAP)对比。与同期印度洋季风强度变化存在极高的一致性(特别是在氧同位素阶段3)。我们认为,全球冰量变化可能不是控制青藏高原季风演化的决定因素,而其它因素如太阳辐射变化及高原下垫面状况对高原季风演化可能具有更为重要的意义。

LOESS RECORD OF QINGHAI-XIZANG PLATEAU MONSOON VARIATIONS IN THE EASTERN PART OF THE PLATEAUSINCE THE LAST INTERGLACIAL

Garze loess section of 10.7m thick is located at the third terrace of theYalongjiang River ,a tributary of Changjiang River in the eastern Qinghai-XizangPlateau.Six paleosol horizons and five loess layers were found in the section. Organic¹⁴C ages of three samples at the depth of 50cm, 330cm and 420cm are 9 500±1 500aB.P., 20 500± 220aB.P. and 21 400±1 200aB.P., respechvely. Two TL ages at520cm and 700cm depth are 39 700± 400aB. P. and 67 000 1 500aB. P., respectively.Because three paleosol horizons at the bottom can be compared with S₁ in the LoessPlateau, it was eshmared that the bottom of the section is at the boundary betweenMISS and 6.Magnetic susceptibility,CaCO₃ content and total organic carbon content are widelyused as proxies of summer monsoon changes and grain size as proxy of wintermonsoon. These proxies of a loess-paleosol sequence in Garze were measured. Theirvariations show that the eastern part of the Qinghai-Xizang Plateau experienced 5enhanced winter monsoon and 6 enhanced summer monsoon Periods, respectively, sincethe last interglacial. Although the variation of the Qinghai-Xizang Plateau monsooncan be compared with the oxygen isotopic stages in deep sea, outstanding differenceexists between them. The strength of summer monsoon in intorglacials in easternQinghai-Xizang Plateau is not always stronger than that in glacials. The goodcorrelation between variation of monsoon in the plateau and the indian Oceanmonsoon suggested linkage of them in similar forcing factors. Therefore,our resultslead us to conclude that changes of the Qinghai-Xizang Plateau monsoon may not becontrolled by global ice volume. On the contrary, orbital forcing might be responsiblefor climate changes in the northeastern Qinghai-Xizang Plateau at least since the lastinterglasial.