摘要
在4.2 ka BP气候突变事件的影响下,世界主要文明和中国境内大部分新石器时代文化出现断层或崩溃,但中国中原地区的洛阳盆地却支持了河南龙山文化向二里头文化的传承和成功转型,使中国文明得以一脉相承.为探究洛阳盆地这一时期的环境状况和人类活动,在AMS^(14)C年代的支持下,基于HZ-1湿地剖面孢粉分析及磁化率和粒度等指标的分析,本文重建了洛阳盆地4990~3890 cal a BP期间自然环境(植被/水文)和人类活动强度的变化历史.自然环境重建结果显示,4990~4330 cal a BP期间气候较干,灰嘴湿地水较浅;4330~4155 cal a BP期间气候湿润,是灰嘴湿地存在的最盛阶段;4155~3995 cal a BP期间气候变干,灰嘴湿地快速萎缩;3995~3890 cal a BP期间气候短暂变湿后再次转干,发育了一层较薄的强风化层后被黄土覆盖.人类活动强度重建结果表明,4990~4330 cal a BP期间人类活动强度较弱;4330~4155 cal a BP期间人类活动强度有所增加;4155~3995 cal a BP期间人类活动强度明显增强;3995~3890 cal a BP期间人类活动强度再次减弱.用大尺度的视角审视灰嘴记录后,我们发现,在4400~3950 cal a BP时段的亚洲季风减弱期内,长江中下游地区与洛阳盆地所在的黄土高原南缘地区确实捕捉到4.2 ka BP气候突变的信号,但二者的干湿状况却出现了明显的差异,即长江中下游地区的弱东亚季风事件较早出现(4400~4100 cal a BP),而黄土高原南缘地区(包括洛阳盆地)的弱东亚季风事件较晚出现(4200~3950 cal a BP).导致这种差异的主要原因可能是,与ENSO由La Ni?a阶段转向El Ni?o阶段有关的赤道太平洋东西方向的热力梯度和西太平洋副热带高压耦合关系的变化.
Affected by the 4.2 ka BP event,the major ancient civilizations in the world and most of the Neolithic cultures in China suddenly collapsed.However,the Luoyang Basin in the central China hosted the successful transition from Henan Longshan Culture to Erlitou Culture at~4.2 ka BP,and the successful transition made the Chinese civilization the only one in the world that has not been interrupted.To explore the environmental conditions and human activities in the Luoyang Basin at~4.2 ka BP,we analyzed pollen assemblages,magnetic susceptibility,and grain size of HZ-1 section,and reconstructed the histories of the environmental changes(vegetation/hydrology)and the human-activity intensity changes with a chronological support of 17 AMS^(14)C dates.Our reconstruction shows that the climate was relatively dry and the Huizui wetland was under a shallow-watered condition from 4990 to 4330 cal a BP.Subsequently,the climate became rather wet and the wetland was under a relatively deep-watered condition from 4330 to 4155 a BP.Followed was a period from 4155 to 3995 cal a BP when climate became relatively dry again and the wetland returned to a shallow-watered condition.The disappearance of the Huizui wetland at~3995 cal a BP was followed by a wet interval lasting from 3995 to~3955 cal a BP when the contemporary loess was strongly weathered.And,the wet interval was then succeeded by a dry interval lasting from 3955 to 3890 cal a BP during which loess deposition dominated.Our reconstruction of human-activity intensity shows that the intensity was rather weak from 4990 to 4330 cal a BP and increased slightly from 4330 to 4155 cal a BP.The human-activity intensity increased significantly from 4155 to 3995 cal a BP and then decreased considerably from 3995 to 3890 cal a BP.Our examination from a large-scale perspective shows that the 4.2 ka BP event corresponded to a relatively long interval of weakened Asian Monsoon spanning from 4400 to 3950 cal a BP.But,the middle and lower reaches of the Yangtze River basin and the southern margin of the Loess Plateau including the Luoyang Basin seemed to have responded to the weakened Asian Monsoon quite differently.Specifically,the 4.2 ka BP eventrelated weakening of East Asian Summer Monsoon(EASM)occurred during the earlier portion(4400–4100 cal a BP)of the Asian Monsoon weakening period(4400–3950 cal a BP)in the middle and lower reaches of the Yangtze River basin,and it occurred during the later portion of(4200–3950 cal a BP)in the southern margin of the Loess Plateau.We propose here that the change in the coupling relationship between the east-west thermal gradient of Equatorial Pacific(associated with ENSO)and the strength of Western Pacific Subtropical High(WPSH)was the main mechanism for this contrast.In other words,the earlier portion(from 4400 to 4100 cal a BP)of the Asian Monsoon weakening period corresponded with an ENSO negative phase(i.e.,La Ni?o stage),under which the precipitation was low in the middle and lower reaches of the Yangtze River basin and high in the middle and lower reaches of the Yellow River basin.In contrast,the late period(4200–3950 cal a BP)of the Asian Monsoon weakening period corresponded with an ENSO positive phase(i.e.,El Ni?o stage),under which the precipitation was high in the middle and lower reaches of the Yangtze River basin and low in the middle and lower reaches of the Yellow River basin.
作者
陈亮
冯兆东
冉敏
惠争闯
李开封
李洪彬
刘畅
张样洋
Liang Chen;Zhaodong Feng;Min Ran;Zhengchuang Hui;Kaifeng Li;Hongbin Li;Chang Liu;Yangyang Zhang(College of Geography and Environmental Science,Henan University,Kaifeng 475004,China;Key Laboratory of Earth System Observation and Simulation of Henan Province,Kaifeng 475004,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2023年第5期546-562,共17页
Chinese Science Bulletin
基金
国家重点研发计划(2020YFC1521605)
河南大学地理与环境学院优秀青年人才培育项目资助。