Holocene climate change's impact on ecosystems has attracted considerable interest.Although human activities increasingly influenced ecosystems during the Holocene,many paleo-records primarily reconstruct natural environmental changes,often neglecting the pre-instrumental human influenceon ecological responses.To understand ecosystem responses comprehensively,it is essential to consider anthropogenic impacts alongside natural factors.Here,we present a Holocene chironomid record from Qinghai Crater Lake in Tengchong,southwestern China,examining the timing and magnitude of natural and anthropogenic impacts on the lake ecosystem throughout the Holocene.Our results reveal that early to midHolocene chironomid communities,especially in terms of species richness,were mainly driven by rising summer temperatures associated with increased solar radiation.By the late-Holocene,the weakening Indian Summer Monsoon led to fluctuating lake levels and intensified human impacts,impacting both chironomid species richness and community stability.Around 0.8 ka BP,enhanced human disturbances shifted the chironomid community composition from mesotrophic taxa dominance(e.g.,Cladotanytasus,Macropelopia)to eutrophic taxa dominance(e.g.,Chironomus,Polypedilum).Over the past few centuries,human influence has further increased chironomid species richness but has led to declining community stability.
Enlou ZHANGWenxiu ZHENGYanmin CAOZhenyu NIYanjie ZHAOWeiwei SUN
High-resolution,continuous Late Holocene lacustrine records are scarce in the Qaidam Basin,but is of especially important for our understanding the future climate variability in the western China.Here,we use grain size,element content and XRD-identified data from the Lake Hurleg in the eastern Qaidam Basin to present the Late Holocene climate variability,which have been temporally constrained using 210Pb-,137Cs-and AMS 14C dating.Our records demonstrate that decreased precipitation climate occurred at~800–1000 yr and~1300–1800 yr intervals,and increased precipitation occurred at~354–800 yr,~1000–1300 yr and~1800 yr to the present.The results show that the Qaidam Basin has undergone a process of warming and humidification since the Industrial Revolution,which is consistent with the meteorological records.The climate in the northeastern Qaidam Basin is dominated by the Asian Monsoon.
重建我国东部季风区全新世水文气候变化历史对于理解东亚夏季风的驱动机制及预测其未来变化十分重要,然而,迄今为止,对我国华南地区全新世水文气候变化的认识还不够清晰。本文在广西桂林岩溶湿地八仙岩获取了一连续沉积剖面(BX),对其开展了AMS^(14)C定年及粒度分析,探讨了该区域中全新世以来的水文气候变化。通过端元模型分析(EMMA)提取了具有明确环境指示意义的三个粒度端元(EM1-3),其中,EM1代表了湿地水位变化,间接指示季风降水;EM3指示极端水文事件。据此,恢复了研究区8.5 ka BP以来湿地演化及季风降水变化历史。结果表明,8.5 ka BP以来区域降水呈逐渐减少的趋势,并可划分为三个阶段:8.5~6.35 ka BP,区域降水丰富,八仙岩发育浅水湖泊;6.35~4.15 ka BP,区域气候逐渐变干,八仙岩退化为湖沼湿地,其中在6.25~6 ka BP、5.2~4.9 ka BP和~4.5 ka BP发生了三次极端水文事件;4.15~0.15 ka BP,湿地水位持续降低,但在1.3~0.7 ka BP有短暂回升。区域对比分析表明,八仙岩沉积记录的季风降水变化历史与东亚夏季风强度变化趋势一致。周期分析还表明,太阳活动是我国华南地区季风降水变化的主要控制因素。此外,低纬海-气相互作用过程(如ENSO)对我国华南地区的季风降水也有重要影响。
淮河流域特大暴雨洪水灾害严重威胁经济社会发展,其防洪减灾和水资源开发利用,急需超长时间尺度河流洪水水文学数据资料的支撑。全新世古洪水水文学的研究,为淮河流域全新世洪水水文数据发掘提供了重要途径。利用河流地貌学、沉积学、水文学和年代学等多学科交叉的方法,获取淮河中上游全新世万年来实际发生过的特大暴雨洪水事件的沉积学记录,采用多种水文模型模拟恢复与检验,获得古洪水事件的洪峰水位和流量数据。淮河干流桐柏东段基岩峡谷的研究发现,过去10 000 a以来发生多次特大洪水事件,尤其是发生在3.1 ka B.P.和1.5 ka B.P.时期的古洪水事件,洪峰水位最高,洪峰流量可达14 300~16 000 m^(3)/s,淮河支流汝河遂平段的调查研究和测年断代表明,在(12.0-11.2) ka B.P.、(4.2-4.0) ka B.P.和(3.2-3.0) ka B.P.,分别发生过3期古洪水事件。而支流沙河在(1.45-1.55) ka B.P.发生过特大泛滥洪水事件,对应于中国历史上南北朝时期的严重气候恶化阶段。这些时段处在全球性气候事件、气候恶化或气候转折阶段。在这些时段,季风状态极其不稳定,变率增大,导致气候异常,极端性变化频繁,既有严重干旱,又有特大洪水事件发生。因此,在全新世来说,淮河流域特大暴雨洪水事件并不必然的与温暖湿润气候阶段相联系。这些研究丰富了高分辨率气候水文事件的内涵,对于深刻理解区域气候水文系统对于全球变化的响应规律具有重要的科学意义。
动物的驯化为人类提供了稳定可靠的食物来源,野牦牛是青藏高原的特有物种,在高原地区人类生活中有着不可替代的作用。本文搜集了现今青藏高原野牦牛分布数据291个,利用MaxEnt模型模拟了全新世(11.0—3.0 ka BP)每间隔500 a以来青藏高原野牦牛适生区的时空演变,适生区模拟精度均达到0.9以上。结果表明影响高原上野牦牛适生区的主要环境因子有最冷季度平均温度、降水量变异系数、最湿季度降水量和每年积雪天数。从时空分布来看,全新世早期(11.0—9.0 ka BP)分布面积最小,主要分布在哈拉湖、藏北高原东部、藏南高山谷地东段及昆仑山西段山地高原区等地;全新世早中期(9.0—6.0 ka BP)分布面积介于全新世早期和全新世中晚期之间,主要分布在祁连山脉、藏北高原西部及青南高原等地区。全新世中晚期(6.0—3.0 ka BP)分布面积达到最大值,主要分布在青海湖盆地、藏北高原、羌塘高原、长江—澜沧江上游等地。全新世以来野牦牛的适生区整体呈现逐渐扩大的趋势,其原因可能与气候环境演变有关。结合极端环境指数和野牦牛适生区指数综合计算,推测野牦牛潜在驯化时间在4.5—4.0 ka BP左右,潜在驯化区在青海湖盆地和长江—澜沧江上游及横断山脉。
黄河作为世界性大河,在世界源-汇系统中扮演着举足轻重的角色,其汇区是探讨有机碳埋藏的热点区域。但目前对黄河水下三角洲的碳埋藏过程的研究多聚焦于其现代沉积过程,对千年尺度水下三角洲地区的碳埋藏过程的认识仍较为缺乏。鉴此,本研究在前期开展的、基于水下三角洲地区浅地层剖面资料的地震地层学研究的基础上,开展BHB1岩芯上部594.8 cm的岩性(包含沉积物粒度等指标)分析,构建地层年代框架,对各沉积单元沉积物开展BHB1岩芯总有机碳(TOC)、总碳(TC)、总氮(TN)和稳定碳同位素(δ13C)测试分析。结果表明,研究区中晚全新世以来的水下三角洲沉积系统自下而上可划分为3个沉积单元(DU1~3), DU1~3形成的时间大致分别分别对应7~6 cal.ka B. P.、 6~3 cal.ka B. P.和公元1855年以来(对应现代黄河三角洲)。BHB1岩芯中晚全新世以来的沉积物呈海陆源混合来源,双端元模型计算显示海源自生有机质占据主导(53%),但海陆源贡献相差不大。沉积速率对有机碳质量累积速率(OC_(MAR))起决定性作用。中晚全新世以来,黄河水下三角洲的平均OC_(MAR)为(13.75 g/(m^(2)·a)),低于黄河水上三角洲(66.55 g/(m^(2)·a)),推测主要受沉积运输距离所影响。此外,7~3 cal.ka B. P.的有机碳埋藏亦显著受控于气候因素;4.5 cal.ka B. P.以来陆源有机碳占比(TOM%)出现显著下降,推测与全新世中后期的两次季风急剧减弱事件有关;1855年以来,现代黄河三角洲的演化进程受人类活动影响剧烈,整体上加速了有机碳埋藏。
It is widely accepted that Holocene climatic and environmental changes had major impacts on socioeconomic development and the evolution of civilization.The eastern margin of the Tibetan plateau(TP)has been an important passageway for south‒north migration of agricultural groups since the late Neolithic.Prehistoric farmers began to occupy the northeastern Tibetan plateau(NETP)and the area of modern Yunnan Province(YNP),on the southeastern margin of the TP,from∼5200 BP and∼4600 BP,respectively.This occupation was potentially closely linked to climatic and environmental changes;however,the spatiotemporal pattern of moisture variations between these two regions,and its possible impact on human settlement and the migration of farming communities along the eastern margin of the TP during the late Neolithic and Bronze Age,are unclear.In the present study,well-dated sedimentary records with unambiguous indicators of humidity variations from the NETP and YNP were integrated,along with radiocarbon dates from human and animal bones and the remains of crop plants from archaeological sites in this region.The results indicate a long-term,out-of-phase relationship of moisture variations between the NETP and YNP during the middle to late Holocene.A mid-late Holocene increase in humidity on the NETP facilitated the development of agropastoral societies during the period of∼5200‒2200 BP.However,pronounced cooling from∼5000 BP forced the southward dispersal of millet farming groups along the eastern margin of the TP during the fifth millennium BP.Decreasing moisture in YNP promoted the expansion of an open landscape,which affected the development of agriculture during the period of∼4600‒2200 BP.Our results suggest that changes in moisture affected the development of prehistoric agriculture in the northeastern and southeastern marginal areas of the TP in different ways,implying that the development of prehistoric human society largely depended on the regional climatic conditions.
Duo WuMinmin MaYongxiu LuShilong GuoTao WangXuyi MaGuanghui Dong
Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experienced significant seismic events,particularly along its northern boundary,highlighting the recurrent seismic activity in the Kyrgyz Republic.The Issyk-Ata fault,stretching 120 km from west to east in the northern Tien Shan,bounds from the north a young,growing anticline demarcating the foothills of the Kyrgyz Range and the Chui depression.This region is susceptible to strong earthquakes,posing a significant threat to the Chui region and Bishkek,the capital city with over a million residents.The youngest fault in the area is the Issyk-Ata fault,traversing the southern part of Bishkek,where modern construction has obscured its features.This study integrates remote sensing,detailed fieldwork,and paleoseismological investigations to map and analyze surface ruptures,quantify vertical displacements,and assess seismic hazards along the Issyk-Ata fault.Using optically stimulated luminescence and radiocarbon dating,we determined ages for documented paleoseismic events,placing two ancient earthquakes in the Holocene.Magnitude estimates suggest seismic events with magnitudes ranging from 6.6 to 7.1.In the Dzhal area,geological and geomorphological analysis yielded a longterm fault-slip rate of 1.15 mm/a.The Issyk-Ata fault shows variable rupture behavior,with distinct segments demonstrating different seismic characteristics and histories of activity.This variability necessitates comprehensive seismic hazard modeling to better understand and mitigate potential risks in the region.
