内蒙古黄旗海中晚全新世（3580-1630cal．aB．P．）气候环境记录

MID-LATE HOLOCENE （3580- 1630cal.a B.P.）CLIMATE AND ENVIRONMENT RECORDS FROM HUANGQIHAI LAKE IN INNER MONGOLIA

基于内蒙古东南缘黄旗海八台沟（40°50～2′N，113°22′44″E；1280ma．s．1．）剖面135cm厚的湖相地层5个AMS14C年龄的测定以及90块样品的孢粉、直径〉501xm炭屑浓度、元素和粒度等高分辨率指标分析，重建黄旗海中晚全新世（3580—1630cal．aB．P．）的植被和气候环境演化过程。内蒙古黄旗海高分辨率指标记录揭示：3580～1630cal．aB．P．期间的黄旗海流域气候环境具有持续变干的特征，具体表现为：1）3580～3000cal．aB．P．间，黄旗海湖面较高，湖泊水位在129lm以上，高于现今湖面23m以上，且最高湖面出现在3380cal．aB．P．之前，之后湖泊水位有所下降；3380cal．aB．P．之前植被类型为针一阔混交林，之后转变为以松属为主的针叶林，气候凉湿。2）3000cal．aB．P．前后的约100年间，黄旗海快速变冷变干，湖泊迅速萎缩，植被转变为草甸草原；之后约1400年内，气候逐渐变干，温度有所上升，气候环境以暖干为特征；1630cal．aB．P．前后黄旗海湖面降到高出现在湖面不足9m的高度以下，之后再未出现超过此高度的湖侵。

Huangqihai Lake （an inland closed lake, 40°41′- 41°43′N, 112°49′- 113°40′E） in the southeastern edge of Inner Mongolia, is located at the north boundary of East Asian summer monsoon. The climate of this area is typical arid to semi-arid, and the lake level of Huangqihai Lake is 1268m a.s.l. A 250em-deep profile was obtained at Baitaigou （40°50′02″N, 113°22′44″E; 1280m a.s. 1.） in Huangqihai Lake area. We studied the 135era in middle part of the profile （230-95cm） and 90 samples （at 1.5cma intervals） were collected. 5 AMS 14C dates in the 135era-deep profile demonstrate that the lacustrine layer （230 - 100cm） is from 3580 cal.a B.P. to 1630 eal.a B.P. （Mid-Late Holoeene）. Based on high resolution proxies of pollen, charcoal （φ〉50μm） content, elemental geochemistry and grain size analysis, the climatic evolution of Huangqihai Lake region in Mid-Late Holoeene was reconstructed. Our data suggest that the climate of the Huangqihai Lake drainage was drying from 3580cal.a B.P. to 1630eal.a B.P., which is indicated by the following aspects. （1） From 3580eal.a B.P. to 3000eal.a B.P., the lake level of Huangqihai Lake was above 1291m a.s.l., 23m higher than the modern lake level. The lake level reached its maximum at around 3380cal.a B.P., and decreased afterwards. The lake level fall coincides with a transition to a colder and wetter climate, as deduced from vegetation changes （coniferous and broadleaved mixed forest to coniferous forests dominated by Pinus）. （2） During a 100 years period around 3000eal.a B.P., the Huangqihai Lake region underwent fast cooling and drying, accompanied by a rapid shrinkage of lake and change of vegetation type to grassland. During the subsequent 1400 years, climate changed to be dry and warm gradually. Around 1630 eal.a B.P., the Huangqihai Lake fell to a lake level less than 9m higher than the present lake level, and never reached this height since then.