末次冰消期滇西地区气候突变事件:湖泊孢粉记录

在末次冰消期总体持续增温的过程中,全球气候经历了一系列以"快速增温/降温"为主要特征的千-数十年尺度的突变事件.由于这些气候突变事件具有明显的高频特性,需要在全球范围不同地区开展更多高分辨率的古气候研究,用于进行突变事件的对比和机制的探讨.本研究对比滇西南腾冲青海湖、滇西北泸沽湖和高山湖泊天才湖约2万以来的孢粉、炭屑记录,揭示了中国滇西地区末次冰消期的植被演替与气候变化历史,探讨了末次冰消期存在的气候突变事件.结果表明,滇西地区末次冰消期开始转暖发生在约19 ka(1 ka=1000 cal. a B. P.);冰消期开始以后,滇西地区气候普遍依次在 17. 5±0. 5~15. 2±0. 1 ka期间、 15. 2±0. 1~14. 3±0. 1 ka期间、 14. 3± 0. 1~12. 9±0. 1 ka期间和12. 9±0. 1~11. 7±0. 2 ka期间存在冷干-逐渐变暖变湿-明显更暖湿-温度湿度略有下降等这几个突变事件,它们在时间上分别对应于H1冷事件、波令前增暖期、 B/A暖期和YD冷事件;滇西地区比较一致地在 11. 7±0. 2 ka进入全新世.除此之外,滇西北地区在约17. 7~17. 0 ka期间可能还存在一次短暂的较明显的暖湿期.对末次冰消期气候变化机制的探讨认为,末次冰消期开始转暖及以后逐渐增温的趋势主要受夏季太阳辐射量从约20 ka逐渐增加,到11 ka左右达到峰值的控制;而末次冰消期发生的气候突变事件如H1冷事件、波令前增暖期、 B/A暖期和YD冷事件主要是受大西洋温盐环流的影响,同时温室气体浓度的变化也起了重要的调制作用.

Climatic abrupt events during the last deglaciation in the western Yunnan Province revealed by pollen records

In the course of overall continuous warming during the last deglaciation, the global climate has experienced a series of millennial-and centennial-scale abrupt events characterized by rapid warming or cooling.Because of the obvious high frequency characteristics of these abrupt events, more high-resolution palaeoclimate studies in different regions around the world are needed for comparison and mechanism discussion of these events.Western Yunnan Province is located to the southeastern margin of the Qinghai-Tibetan Plateau, which is topographically complex with many mountain ranges running roughly north to south and separated by parallel, deep and narrowly incised river valleys.The span of latitude and altitude differences are large, and the elevation of the region ranges from about 1000 m to above 5000 m.Qinghai Lake, Tiancai Lake and Lugu Lake are all located in western Yunnan Province (the west of 101° E).Their altitudes are 1885 m, 3898 m and 2690 m, respectively.This paper compared synthetically the pollen and charcoal records between ca.20 ka and 10 ka from the sediment cores of these three lakes, and discussed the history of vegetation evolution and climatic changes, and explored the possible climatic abrupt events during the last deglacial period.The data include 114 pollen and charcoal samples from Qinghai Lake, 110 pollen samples from Tiancai Lake, and 122 pollen samples from Lugu Lake during the last deglacial period.The results show that the initial Late Glacial warming in western Yunnan Province occurred at ca.19.0 ka (1 ka=1000 cal.a B.P.).After the initial Late Glacial warming, there are several climatic abrupt events in western Yunnan Province, namely, a cold and dry climatic condition during the period 17.5±0.5~15.2±0.1 ka, a gradually warming and humidifying climatic condition between 15.2±0.1 and 14.3±0.1 ka, an obviously warmer and wetter climatic condition from 14.3±0.1 ka to 12.9±0.1 ka, and then a slight decrease in temperature and humidity during the period 12.9±0.1~11.7±0.2 ka.These climatic abrupt events correspond to the Heinrich Event 1 (H1), the pre-B?lling warming, the B?lling-Aller?d warm period (B/A) and the Younger Dryas event (YD), respectively.In western Yunnan Province, the start of the Holocene is relatively consistently recorded at 11.7±0.2 ka.In addition, there may be a short period with relatively obviously warm and wet climatic condition in western Yunnan Province during the period ca.17.7~17.0 ka.Based on this study, we discussed forcing mechanism of climatic changes during the last deglaciation, and considered that the initial Late Glacial warming and the tendency of gradual increase of temperature may be controlled by summer solar insolation, which increased gradually from ca.20 ka, and then peaked at ca.11 ka.The climatic abrupt events during the last deglaciation such as the H1, the pre-B?lling warming, the B/A and the YD were mainly influenced by the Atlantic meridional overturning circulation (AMOC).At the same time, the variations in greenhouse gas concentrations also play an important modulation role.