末次冰消期以来赛里木湖沉积记录的气候突变

末次冰消期以来的气候突变事件的时空变化特征及其区域响应是古气候环境变化研究的重要内容,然而亚洲中部干旱区末次冰消期以来的气候突变记录较少,尤其缺少末次冰消期期间快速转暖过程的区域响应.本研究通过对位于亚洲中部干旱区的新疆西天山中部亚高山湖泊赛里木湖湖心采得的长300 cm的SLM2009钻孔沉积物的碳酸盐含量和粒度变化特征的分析,在 14 个 AMS 14C测年数据的基础上,探讨了末次冰消期约23. 4 cal. ka B. P.以来亚洲中部干旱区的气候突变事件记录及其区域响应过程.结果表明:赛里木湖湖心钻孔沉积物完整记录了 H1 ( 17. 5 ~ 15. 2 cal. ka B. P.)、 YD ( 12. 6 ~ 11. 7 cal. ka B. P.)冷事件以及 B-A ( 15. 2 ~12. 9 cal. ka B. P.)暖事件等末次冰消期气候突变事件以及全新世以来的10. 5 ka、 8. 2 ka、 5. 5 ka、 4. 2 ka、 2. 8 ka和小冰期冷事件,这与亚洲中部干旱区已有的气候突变事件记录相吻合,表明末次冰消期以来亚洲中部干旱区具有相似的气候突变演化模式.同时这些气候突变事件与高纬冰芯以及低纬石笋氧同位素记录的一致性则表明气候突变具有全球性影响,受相同的成因机制因素控制.

Abrupt climate events recorded by Sayram Lake sediments since the last deglaciation

Temporal and spatial variations and regional responses of abrupt climatic events since the last deglaciation are important contents of paleoclimate and environmental change research. However, there are few records of abrupt climatic events since the last deglaciation in arid Central Asia, especially the regional response of rapid warming process during the last deglaciation. Based on the analysis of carbonate content and grain size of borehole sediments in Sayram Lake (44°30'~44°42'N, 81°05'~81°15'E), a sub-alpine lake in the central part of the Western Tianshan Mountains, Xinjiang, the records of climatic abrupt events and their regional response processes in arid Central Asia since the last deglaciation were discussed. In this study, a 300-cm sediment core was recovered at the depth of 86.0 m in the center of Sayram Lake. The core was sub-sampled at 2 cm intervals and a total of 149 carbonate content and grain size samples were analyzed throughout the record. The relationship between the carbonate content and grain size and the paleoenvironmental changes from Sayram Lake, Xinjiang was investigated. The record covers periods since 23.4 cal.ka B. P. to the present and is based on the analysis of 14 AMS radiocarbon 14C dates using bulk organic matter from the lake sediment. The average time resolution of 149 samples is 156 a, of which 23.4~16.6 cal.ka B. P. is 247 a, 16.6~8.6 cal.ka B. P. is 810 a and 8.6~0 cal.ka B. P. is 70 a. Carbonate in sediments of Sayram Lake mainly depends on the intense evaporation and concentration of lake water caused by high temperature in summer and the consumption of CO2 in water by biological activities, which results in the formation of carbonate supersaturated precipitation. Therefore, the change of carbonate content indicates the variation of regional temperature. Carbonate content decreased significantly during the period of 17.4~15.2 cal.ka B. P., 12.6~11.7 cal.ka B. P., 10.6~10.3 cal.ka B. P., 8.4~8.0 cal.ka B. P., 6.0~5.4 cal.ka B. P., 4.4~4.0 cal.ka B. P., 3.0~2.7 cal.ka B. P. and 0.7~0.4 cal.ka B. P. indicating a decrease in temperature. These cold events correspond to Heinrich 1 (H1) and Younger Dryas (YD) cold events since the deglacial period, and 10.5 ka, 8.2 ka, 5.5 ka, 4.2 ka, 2.8 ka and Little Ice Age cold events since the Holocene respectively. A rapid increase in carbonate content during the period of 15.2~12.9 cal.ka B. P. indicated a rise in temperature, corresponding to B?lling-Aller?d (B-A) warm events. The change of grain size of Sayram Lake directly reflects the change of lake level, and the increase of coarse grain content reflects the decrease of lake level and the drought of climate. The content of coarse grain increased significantly during 17.4~15.2 cal.ka B. P., 12.6~11.7 cal.ka B. P., 8.4~8.0 cal.ka B. P., 6.0~5.4 cal.ka B. P. and 4.4~4.0 cal.ka B. P., which were consistent with the indicators of the reduction of carbonate. It further supported the drought of climate and the decrease of lake level during the cold events of H1, YD, 8.2 ka, 5.5 ka and 4.2 ka. When the lake level reaches a certain depth, the grain size is slightly affected by abrupt climatic events. So, since 4.0 cal.ka B. P., the content of coarse grains has been relatively stable, and the change is not obvious, indicating that the climate is wet and the lake level rises during this period. In addition, the carbonate content and the percentage of coarse grain in 7.4 cal.ka B. P. and 6.8 cal.ka B. P. also indicated two obvious event records, reflecting the climate instability during this period. The above results are consistent with the existing records of climate abrupt events in the arid Central Asia. It shows that there is a similar evolution model of abrupt climate change in this area since the last deglaciation. At the same time, the consistency of these abrupt climatic events with high latitude ice cores and low latitude stalagmite records indicates that the abrupt climatic events have global impact and are controlled by the same genetic factors.