兰州不同时期黄土有机质碳同位素与气候的关系

Relationship between the δ^(13)C of Organic Matter in the Paleosoil at Different Stage with the Climatic Change in Lanzhou

基于兰州九州台黄土剖面的土壤有机质δ1 3C分析 ,讨论了兰州地区末次间冰期和全新世 2个时期气候以及地表植被的变化特征。结果表明 ,该地区末次间冰期δ1 3C变化范围为 -2 9 97‰～ - 2 5 52‰ ,平均值为 - 2 7 79‰ ;全新世δ1 3C变化范围在 - 2 0 82～ - 34 40‰之间 ,平均值为 - 2 8 99‰。从δ1 3C平均值来看 ,该地区在以上两个时期地表植被主要为C3植物。末次间冰期九州台剖面δ1 3C表现出 3峰夹 2谷的特征与同一时期深海SPECMAP曲线有着良好的对应 ,表明了该时期兰州地区的气候变化与全球是一致的 ,全新世土壤有机质δ1 3C所反映出的 3个不同的变化阶段对应于早、中、晚全新世阶段。结合黄土高原其他剖面相应时期的土壤有机质δ1 3C的研究结果 ,我们观察到陕西关中地区的黄土剖面末次间冰期和全新世土壤有机质δ1 3C要大于黄土高原西部的兰州等地区 ,气候差异引起的地表植被中C3、C4 植物比例不同是造成两地区土壤有机质δ1 3C差异的主要因素。研究结果表明 ,黄土高原土壤有机质δ1 3C是揭示该地区气候变化的一个良好代用指标。

On the basis of the carbon isotopic analysis of the organic matter in the paleosoils from the Jiuzhoutai S 1 and S 0 profiles it shows that the values of δ 13C from the S 1 profile are from -29.97‰ to -25.52‰, with the average of -27.79‰, and that from S 0 are from -34.40‰ to -20.82‰, average is -28.99‰. The main vegetation during the two stages is C 3, and during the warm and humid periods less C 4 vegetation appeared. Combining the result of the SPECMAP we observed that three peaks and two valleys appear at the curve of δ 13C during the last Interglacial period, suggest that the climatic change characteristic at Lanzhou area is the same with the global. Three different climatic stages are also reflected on the δ 13C variation during the Holocene. Comparing the δ 13C results of other profiles in the Loess Plateau, the carbon isotopic values increase from profiles in Shaanxi Province to Lanzhou area, Gansu Province. Different climatic conditions at the two areas are the main factor that resulted such δ 13C variation.