21kaB.P.以来大兴安岭中段月亮湖沉积物全岩有机碳同位素组成变化及其古气候意义

月亮湖是位于大兴安岭中段阿尔山-柴河火山区的一个火山口湖,地处现今季风/非季风影响的过渡地带,对气候环境变化反应敏感。月亮湖长约9m的沉积岩芯记录了21cal.kaB.P.来的古气候演化历史。月亮湖沉积物全岩有机碳同位素组成( δ13 Corg)、总有机碳含量(TOC)和总氮含量(TN)分析结果表明: δ13 Corg值分布范围为 -34.3 ‰ ~-24.8 ‰ ,具有9.5 ‰ 的变化幅度,但总体仍然在陆生C3植物的变化范围内。TOC含量分布范围为1.04 ％ ~23.55 ％ ,TN含量分布范围为0.08 ％ ~1.78 ％ ,TOC与TN含量变化趋势相同,呈正相关性,两者都显示出末次冰期晚期时含量特别低的特征。沉积物的 TOC/TN 比值(原子比)分布范围为6.3~28.2,其中末次冰期晚期的值比较低,说明沉积物中有机质以内源水生生物为主,其后 TOC/TN 比值明显升高且多>14,说明大部分有机质来源于汇水盆地中的陆生植物。根据多个指标综合分析,有效湿度的影响很可能是 δ13 Corg 变化的主导因素。因此,近2万年来月亮湖全岩有机碳同位素组成变化与古气候变化的对应关系是: 暖湿气候对应着偏负的 δ13 Corg值,冷干气候对应着偏正的 δ13 Corg值,全新世期间因植被变化不大,其 δ13 Corg值变化幅度也不大。

STABLE CARBON ISOTOPE RECORD OF BULK ORGANIC MATTER FROM A SEDIMENT CORE AT MOON LAKE IN THE MIDDLE PART OF THE DAXING'AN MOUNTAIN RANGE, NORTHEAST CHINA DURING THE LAST 21ka

Moon Lake,a crater lake at the Aershan-Chaihe Volcanic Field in the middle part of the Daxing'an Mountain Range,Northeast China,is located at the current northern margin of the East Asian summer monsoon that represents a particularly sensitive region to climate changes.A 9-m-long sediment core recovered at Moon Lake was analyzed for stable carbon isotope of bulk sediment organic matter( δ13 Corg),and total organic carbon(TOC)and total nitrogen(TN)contents to understand the process of changes in the climatic condition during the last 21ka.The data indicate that δ13 Corg varies from -34.3 ‰ to -24.8 ‰ and falls within the range of δ13 C of terrestrial C3 plants.TOC and TN range from 1.04 ％ to 23.55 ％ and from 0.08 ％ to 1.78 ％ with low contents at the end of the Last Glaciation,and display a similar pattern of changes in the content.The atomic ratios of TOC to TN ranging from 6.3 to 28.2 were lower at the end of the Last Glaciation,indicating aquatic origins of the lacustrine organic matter,and increased up to over 14 during the Holocene,implying the predominant contribution from terrestrial plants. δ13 Corg is interpreted to reflect regional effective humidity based on multi-proxy analyses.It became lighter under warmer and wetter conditions and shifted towards heavier values when the climate was colder and drier.During the Holocene, δ13 Corg remains almost unchanged,denoting no obvious variations in the vegetation around Moon Lake.