巫山黄土是指分布于长江三峡地区的黄土状堆积物,是中国黄土的重要组成部分,具有重要的古气候环境意义.微生物四醚膜脂是反演古气候环境的灵敏指标,为了进一步理解巫山黄土中蕴含的古气候意义,通过测定巫山黄土中微生物醚类化合物(glycerol dialkyl glycerol tetraethers,GDGTs)并分析其分布特征,基于支链GDGTs(bGDGTs)的甲基化指数(methylation index of branched tetraethers,MBT)和环化指数(cyclization ration of branched tetraethers,CBT)重建该地44.4~ 22.8ka.BP的古温度年平均气温(mean annual air temperature,MAAT),MAAT与频率磁化率曲线和北大西洋沉积物有孔虫曲线对比,其变化趋势具有一致性,反映了其指标的可靠性.巫山黄土的陆源输入指数(BIT值,bGDGTs vs.crenarchaeol)在0.5~1.0之间,大部分值接近于1.0,但有几个极低值,分析为干旱事件.根据MAAT和BIT指标,巫山地区在冰期气候有剧烈的波动,在36.23.6ka.BP、26.02.7ka.BP、23.72.3ka.BP时相对比较干旱,推测可能分别对应着H4、H3和H2事件,表明该区气候变化响应全球气候变化.
英文摘要:
Wushan loess,regarded as the southern boundary of Chinese Loess,is distributed in the Three Gorges area in the Yangtze River,which contains rich paleoclimatic information attracting attentions of many scholars in paleoclimate.In order to further reveal its causes and better understand the paleoclimatic significance contained in Wushan loess,the glycerol dialkyl glycerol tetraethers(GDGTs)extracted from Wushan loess section were investigated.Comparing the mean annual air temperature( MAAT)reconstructed based on branched GDGTs (bGDGTs)with frequency-dependent magnetic susceptibility and North Atlantic sediments,it is found that the three curves are analogous in climate evolution patterns.These similarities show that climatic changes in Wushan region respond to global climatic changes.The BIT values range from 0.5-1.0and most BIT (bGDGTs vs.crenarchaeol)values are close to 1.The low BIT values suggest that it was very dry at 36.2ka.BP,30.2ka.BP and 23.5ka.BP.Based on MAAT and BIT values,it is found that it was relatively cold when it was very dry.It is proposed that the three periods correspond to H4,H3,H2climate events,respectively.