【摘要】 中国西北地区众多封闭湖泊湖岸堤的光释光(OSL)测年结果表明,“大湖”存在于深海氧同位素第5阶段(MIS5)或者更早,而不是MIS3阶段。由于高湖面测年结果的变化,我们对中国西北以及青藏高原地区湖泊对晚第四纪冰期-间冰期旋回气候变化响应的认识也随之改变。本研究对青海湖周边的湖岸堤、湖相沉积物、冲积和风成沉积物进行光释光测年,重建了青海湖末次间冰期以来的高湖面演化历史,得到以下结论:1)最高湖面(拔湖26～66m)出现在MIS 5时期;2)MIS 3c时期湖面高出现在约13～171 m,但是在MIS 3a阶段湖面下降至接近于中全新世湖面高度;3)全新世最高湖面出现在距今约5.1 ka,湖面至少高出现在9.1m,之后在约2ka前再一次出现高湖面,高出现在湖面约8m。青海湖高湖面的拔湖高度从MIS 5a到MIS 3时期,再到全新世是依次降低的,使得早期的湖岸堤没有被后期高湖面破坏而较好的保存了下来。更多还原

【Abstract】 Recent Optically Stimulated Luminescence( OSL) dating of numerous closed-basin lake shorelines in northwestern China has shown that the "Greatest Lakes" period in the region occurred during MIS 5 or earlier,rather than during MIS 3.However, this shift in the chronology of lake highstands means that we now know little about the relative responses of lakes in northwestern China and Qinghai-Tibetan Plateau to East Asian Summer Monsoon( EASM) shifts during various late Quaternary interglacial/interstadial periods.Qinghai Lake is the largest brackish lake in China, located within a closed-basin, on the northeastern Qinghai-Tibetan Plateau.Its size and proximity to three climate systems( EASM, Indian Summer Monsoon, and Westerlies) makes it sensitive to global climate changes.We have conducted geomorphic and stratigraphic survey around the Qinghai Lake for more than ten years, and dated more than one hundred sedimentary samples by OSL dating.In total, about 50 shoreline or lacustrine sediment ages were reported during the past several years.As the quartz OSL ages may approach their upper dating limits( saturation level) at about 60 ～80 ka,we conducted K-feldspar dating( post-IR IRSL) for another four shoreline and near-shore sediments(their quartz OSL ages lie in MIS 5a stage) due to the post-IR IRSL dating can get reliable burial ages as old as 200 ka, and the K-feldspar dating results in accordance with previously reported quartz OSL ages.Then we reconstruct a detailed history of Qinghai Lake highstands using OSL dating of shoreline, lacustrine,alluvial,and aeolian deposits spanning MIS 5 ～Present.Our results indicate:( 1) The highest lake levels(26～66 m above modern) occurred during MIS 5;(2) MIS 3 lake levels initially reached ca.3213 m,but fell during the latter half of MIS 3 to near or below mid-Holocene levels(≥3203 m);( 3) The Holocene highest highstand occurred between ca.5 ～ 6 ka when the lake level was ≥9.1 m above present, with a second highstand reaching 3202.3 m occurring during the Late Holocene at ca.2 ka.This shoreline history suggests higher lake levels are primarily associated with an enhanced EASM, and that the overall lake levels have decreased over the last three interglacial/interstadial cycles.更多还原