东海嵊山岛末次冰期黄土有机碳同位素特征及其古环境意义

黄土沉积中有机碳同位素组成与古气候关系密切，对研究区域环境演变具有重要意义。本文聚焦我国东海嵊山岛末次冰期黄土地层，在磁化率和元素地球化学指标特征分析基础上，开展有机碳同位素组成特征研究。研究结果表明：嵊山岛黄土沉积剖面有机碳同位素组成波动范围−21.63‰～−27.56‰，平均值为−24.88‰，剖面有机碳同位素组成波动偏正；利用端元法对嵊山岛黄土沉积环境中C3/C4植被相对丰度进行估算，揭示沉积地层记录的植被类型是以C3型植被为主导，C4型植被对沉积地层中有机碳同位素的贡献有限；与南京洞穴石笋、苏禄海海洋沉积以及南极Vostok冰芯氧同位素记录对比，显示末次冰期间冰阶时期嵊山岛黄土沉积中有机碳同位素波动是以C3型植被为主导的植被碳同位素对降水条件改变的响应，降水可能是这一时期黄土沉积中有机碳同位素变化的主要影响因素；在末次冰消期阶段，温度有利于C4植被的发育，导致区域C4型植被丰度有所上升，并对沉积地层中有机碳同位素变动的贡献增加。

Characteristics of organic carbon isotope and the paleoenvironmental significances of loess in Shengshan Island during the Last Glacial Period

The organic carbon isotope composition in loess deposits is closely related to paleoclimate, which is of great significance to the study of regional environmental evolution. The loess deposit of the Last Glacial Period in Shengshan Island in the East China Sea off the East China was studied. The magnetic susceptibility and element geochemistry were analyzed, based on which the organic carbon isotope composition was scrutinized. Results show that since the Last Glaciation, the organic carbon isotope composition in the loess fluctuated from −21.63‰ to −27.56‰ on average of −24.88‰. In general, the value of organic carbon isotope decreased with the increase in burial depth of the loess. In addition, the relative abundance of C3/C4 vegetation in Shengshan Island was estimated by using the end-member method. It was revealed that the C3 plants dominated in the island since the Last Glacial Period, and C4 plants were very limited in the contribution to the organic carbon isotope in the loess deposit. In comparison with the oxygen isotope data of the cave stalagmites in Nanjing, marine sediments from Sulu Sea, and Antarctic Vostok ice core, the loess was deposited during the interstage of the Last Glaciation, and the fluctuation in organic carbon isotope value was resulted mainly from the responses of local ancient C3 plant-dominated vegetation to the variation of precipitation condition. The precipitation was the main influential factor on the organic carbon isotope variation during the period. In the last deglaciation stage, the paleo-temperature favored C4 plants booming, thus the relative abundance of C4 plants increased, and so did their contribution to the fluctuation of organic carbon isotopes in the loess deposits in the island.