Peat record reflecting Holocene climatic change in the Zoigê Plateau and AMS radiocarbon dating

Through the use of reliable AMS dating of high resolution (15–30 years) peat and the establishment of monsoon climate proxies sequence, we have been able to recognize several cold, dry events in the Tibetan Plateau during the Holocene. The more obvious ones occurred around 12800, 11300, 10200, 9580, 8900, 6400, 4400, 3700, 2800 and 1500 cal. aBP. These events correlate well with both ice rafting events recorded in high latitude North Atlantic Ocean sediment cores and cooling events in the low latitude SST. Spectral analysis indicates high frequency climate variation on centennial-millennial time scale during the Holocene. This further reflects Holocene climate instability and the existence of centennial-millenium scale rhythm in mid latitude areas as well.     

Millennial-scale climate change since the last glaciation recorded by grain sizes of loess deposits on the northeastern Tibetan Plateau

Whether climatic changes in high latitudes of the Northern Hemisphere since the last glaciation have effects on the Tibetan Plateau monsoon, and the variation characteristics of the Plateau monsoon itself are still not solved but of great significance. The 22-m high-resolution Ioess-paleosol sequence in the Hezuo Basin on the northeastern Tibetan Plateau demonstrates that the Plateau winter monsoon experienced a millennial variation similar to high latitude Northern Hemisphere, with cold events clearly correlated with Heinrich events but less for the warm events (Dansgarrd-Oeschger events). It may indicate that the climate system at high latitudes in the Northern Hemisphere had played an important role in both the Plateau monsoon and the high-level westerlies. On 10^4 year scale, there are two distinct anomalous changes, which are not found in the records from high latitude northern hemisphere, revealed by the loess grain size in the Hezuo Basin. One is that there was a considerable grain size increase at -36 kaBP, suggesting an abrupt enhancement of the Plateau winter monsoon at that time; the other is that, during 43--36 kaBP, the grain size decreased distinctly, indicating a notable weakening of the Plateau winter monsoon around that period. Both of the two anomalies suggest that the Tibetan climate may have been controlled by some other factors, besides the high latitude climatic changes in the Northern Hemisphere.     

长江三角洲南翼 PJ孔揭示的全新世突变气候事件分析研究

全新世存在周期性气候突变事件已被多项研究证实,但有关于这些突变气候事件的驱动因子一直存在争议。本项研究通过对长江三角洲南翼PJ钻孔沉积物研究,反演区域全新世期间多次气候突变事件,几次明显的突变事件在500,1900,2900,3800,4500,5800,6800,7800,8500 cal yr BP左右,这些突变气候事件与全球其它地区的研究成果有很好的对比性。本文认为这些突变气候事件在全球范围内都有明显表现,可能是由于全球性气候因子的周期性变化所致,而非局地气候因子引起。     

利用周期性预测未来百年中国气温变化

全球变暖是目前最为重大全球变化事件,全球变暖的未来趋势是关注的焦点之一,过去全球变化的研究,为预测未来气候变化提供了背景资料.采用中国全新世百年分辨率气温集成序列,利用傅立叶分析技术进行周期分析,并结合全新世环境记录的研究结果,以6000a、4000a、3000a、2400a、1200a、1091a、1000a、923a和706a做为自然变率的谐波准周期,对集成序列进行拟合,结果表明：拟合序列与集成气温变化趋势基本一致,能较好的拟合全新世百年尺度冷暖变率,对集成序列的方差解释量达到81%.并利用周期外延的方法预测了未来百年尺度的气温自然变率,未来500年气温将呈现下降趋势,在2300～2400AD气温较现代低1℃左右.太阳因素与全新世气候的周期性变化关系显著,但太阳驱动气候变化的模式复杂,在千-百年尺度利用太阳活动来预测未来气温具有不确定性.     

临汾盆地陶寺遗址附近全新世黄土剖面的环境指标分析

在对临汾盆地陶寺遗址北城墙外全新世黄土剖面粒度、磁化率、Rb/Sr值和CaCO₃含量等气候指标进行分析的基础上, 结合光释光测年结果和考古学资料, 探讨该剖面记录的环境信息及其与文化发展的相互关系。研究发现: 全新世早期(10.5~9.6 kaBP), 东亚冬季风较弱, 风化成壤作用增强, 气候由凉干转向暖湿; 全新世早中期(9.6~4.9 kaBP), 风化成壤作用最强, 气候最为暖湿; 全新世中后期(4.9~2.5 kaBP), 风化成壤作用较之前有所下降, 气候较之前温干, 但较现今暖湿; 全新世晚期(2.5 kaBP)以来, 东亚冬季风增强, 风化成壤作用较弱, 气候较为凉干。暖湿气候期与文化的繁荣发展时期有较好的对应关系, 凉干气候期植被的退化可能受气候和人类活动共同作用的影响。     

Long-term trend and abrupt events of the Holocene Asian monsoon inferred from a stalagmite δ18O record from Shennongjia in Central China

The middle-Holocene was a period of profound cul- ture transitions: the Neolithic culture around Central China[1], Mesopotamia[2] and India[3] all mysteriously collapsed around 4 ka . It is plausible that this civiliza-tion collapse can be contributed to …     

陕西蓝田全新世古气候演化特征

了解最近10 000 a来的植被和环境对制定治理黄土高原及其水土流失的战略方针、预测未来黄土高原的气候变化都具有重要的意义.作者在阐述陕西蓝田县城附近地质环境的基础上,利用孢粉图式分析了该区植被的演替,进而分析了该区全新世的古气候演化特征.据17个样品分析发现孢粉和藻类十分丰富,将孢粉图式分为三个带,分别代表全新世早、中、晚三个时期的孢粉带.Ⅰ带为蒿属优势带;Ⅱ带是乔木花粉激增,早期发育有温带阔叶落叶林或针阔叶混交林,晚期是以温带阔叶树或与松混合的疏林草原或森林草原;Ⅲ带是以栎、蒿为主的森林草原或疏林草原.结果表明早全新世气候较冷较干,发育有以蒿为主的大片草原;中全新世气候温暖湿润,发育了疏林草原和森林草原;晚全新世渐变为干燥而寒冷,是以松、蒿为主的森林草原.     

气候变化背景下我国北方农牧交错带生态风险评价

计算了我国北方农牧交错带中段(冀、蒙、辽交界地带)1961?2007年的气候风险指数,将其与土地易损性系数综合得到生态风险指数,划定生态风险级别,分析气候风险和生态风险的时间序列变化和空间分异规律。得出的结论主要为: 1) 1961 ?2007年,气候风险呈现增加趋势。空间上由东南向西北方向气候风险指数逐渐变大,风险增强;阿巴嘎旗风险极高,浑善达克沙地和科尔沁沙地周围旗县也处在高风险中或者有向高风险变化的趋势。2) 研究区域内,越向北方、向西方的区域生态风险级别越高,风险越大;4级高风险和5级极高风险区域主要集中在阿巴嘎旗南部浑善达克沙地地区和翁牛特旗中北部科尔沁沙地地区。3)生态风险级别较高的地区对草原覆盖度变化、气候变化都表现得更加敏感。     

Interconnections between the Asian monsoon, ENSO, and high northern latitude climate during the Holocene

The International Geosphere Biosphere Program (IGBP), which promotes better understanding of the living environment, was initiated in the early 1990s. IGBP and other programs have uncovered much evi-dence that the Earth system is complex and nonlinear, ex…     

High—resolution records of Holocene from the Shuangchi Maar Lake in Hainan Island

The results of sedimentary characteristics,grain-size,clay mineral,C/N and pollen analysis reveal the evolution history of the Shuangchi Maar Lake of Hainan Island as well as the short-term climate variations in tropical areas.It is testified that the Maar sediment system was sensitive in recording the rapid climate changes in the Holocene.These multidisciplinary results demonstrate that the thermal maximum in the Holocene climate lasted from 7200 to 2700 aBP,with serveral abrupt ephemeral vibrations occurring between 7250-6120aBP and at around 4460,3850 and 2700 aBP.In the late Holocent,particularly at -2700 aBP,a distinct environmental change indicating an important climate transition in the tropical eastern Asia was recorded,probably responding to the enhancement of ENSO phenomena in the Pacific Ocean.In addition,the high-resolution algae record clearly indicates periodical climate fluctuations at 500 a cyclicity during the last 2500 years.     

A 16000-year pollen record of Qinghai Lake and its paleo-climate and paleoenvironment

The paleoclimate and paleoenvironment of Qinghai Lake indicated by a 16000-year pollen record are as follows. It was very cold and dry before 15200 years. During the Late Glacial, the climate varied from colder and semiarid to cool and semi-humid and fluctuated frequently but with little amplitude. Three cold events in the periods of 13400–13000, 11600–12000, and 11000–10400 aBP respectively correspond to the Oldest Dryas, Older Dryas and Younger Dryas events, whereas the two warm periods between them, 12000–13000 and 11600–11000 aBP, respectively correspond to Bölling and Alleröd periods. The temperature increased abruptly after the Younger Dryas event, and then the climate gradually turned to be warm and wet from warm and semiarid. In the Holocene, the largest amplitude of cold event that occurred at ca. 8200 aBP is quite prominent. The Holocene climatic optimum culminated at 6700 aBP. After 2100 aBP, the climate tended to be cold and dry, keeping on up to now. Palaeoclimatic evolution and events of Qinghai Lake based on pollen assemblage and concentrations can be well parallel with the global climatic events.     

Rapid changes of glacial climate simulated in a coupled climate model

Abrupt changes in climate, termed Dansgaard-Oeschger and Heinrich events, have punctuated the last glacial period (approximately 100-10 kyr ago) but not the Holocene (the past 10 kyr). Here we use an intermediate-complexity climate model to investigate the stability of glacial climate, and we find that only one mode of Atlantic Ocean circulation is stable: a cold mode with deep water formation in the Atlantic Ocean south of Iceland. However, a 'warm' circulation mode similar to the present-day Atlantic Ocean is only marginally unstable, and temporary transitions to this warm mode can easily be triggered. This leads to abrupt warm events in the model which share many characteristics of the observed Dansgaard-Oeschger events. For a large freshwater input (such as a large release of icebergs), the model's deep water formation is temporarily switched off, causing no strong cooling in Greenland but warming in Antarctica, as is observed for Heinrich events. Our stability analysis provides an explanation why glacial climate is much more variable than Holocene climate.     

广州地区晚第四纪孢粉气候研究

 利用广州地区南北2个不同沉积地貌区的钻孔进行孢粉分析,结合测年和沉积信息,分析了广州所代表的珠江三角洲地区晚更新世以来的沉积环境和气候变化。孢粉分析结果显示：在晚更新世珠江三角洲地区气候经历了偏冷干-偏凉干-暖湿-热湿-偏凉干-冷干的变化过程,末次冰期对本区具有明显影响,使全新世和晚更新世孢粉组合表现出一定的差异;全新世气候明显转暖湿,整体上以暖湿为主,但出现了一些小的气候波动事件,最明显的是在2 250 a BP 前后偏凉干的变化;该区在晚更新世和全新世各经历过一次海侵,两孔反映的气候期和海平面变化较为一致,气候和海平面变化也有很好的对应。两孔在地层、沉积相和孢粉特征上的差异是地理位置、沉积环境和基座地貌等差异造成的。     

The early Holocene optimum inferred from a hish-resolution pollen record of Husuansyan Maar Lake in southern China

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that （i） pollen percentage of trees and shrubs reached 56% during the early Holocene （11600-7800 cal a BP）, of which the pollen percentage of tropical trees reached a maximum at 9500-8000 cal a BP, reflecting a hot and wet environment; （ii） during the mid-Holocene （7800-4200 cal a BP）, the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; （iii） in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500-8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.     

Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum

Models and palaeoclimate data suggest that the tropical Pacific climate system plays a key part in the mechanisms underlying orbital-scale and abrupt climate change. Atmospheric convection over the western tropical Pacific is a major source of heat and moisture to extratropical regions, and may therefore influence the global climate response to a variety of forcing factors. The response of tropical Pacific convection to changes in global climate boundary conditions, abrupt climate changes and radiative forcing remains uncertain, however. Here we present three absolutely dated oxygen isotope records from stalagmites in northern Borneo that reflect changes in west Pacific warm pool hydrology over the past 27,000 years. Our results suggest that convection over the western tropical Pacific weakened 18,000-20,000 years ago, as tropical Pacific and Antarctic temperatures began to rise during the early stages of deglaciation. Convective activity, as inferred from oxygen isotopes, reached a minimum during Heinrich event 1 (ref. 10), when the Atlantic meridional overturning circulation was weak, pointing to feedbacks between the strength of the overturning circulation and tropical Pacific hydrology. There is no evidence of the Younger Dryas event in the stalagmite records, however, suggesting that different mechanisms operated during these two abrupt deglacial climate events. During the Holocene epoch, convective activity appears to track changes in spring and autumn insolation, highlighting the sensitivity of tropical Pacific convection to external radiative forcing. Together, these findings demonstrate that the tropical Pacific hydrological cycle is sensitive to high-latitude climate processes in both hemispheres, as well as to external radiative forcing, and that it may have a central role in abrupt climate change events.     

Environmental changes during early-middle Holocene from the sediment record of the Chaohu Lake,Anhui Province

A typical lake sediment core is obtained from the Chaohu Lake in the lower reaches of the Yangtze River,Anhui Province,China.The timing scale is constrained by AMS 14 C dating method.Climate proxies such as pollen and grain size in the core are analyzed to reconstruct the environment changes at this site approximately between 9870 and 2170 cal.a BP.The results indicate that at the research area, the climate in the early-middle Holocene had evolved through 3 stages.From 9870 to 6040 cal.a BP, proxy records show a warm and dry climate with low water levels after the late-glacial period.During this stage,cool and dry events occurred at about 8910 and 6060-6030 cal.a BP.Then,between 6040 and 4860 cal.a BP,the climate was humid and vegetation was more flourishing in the Chaohu Lake Valley.The Holocene Optimum occurred at 5840-5500 cal.a BP in the Chaohu Lake,showing the best condition of water and heat.Elm Decline occurred at the period of 5380-4930 cal.a BP.Since 4860 cal.a BP,the climate was warm and dry through 2170 cal.a BP as shown in both pollen spectrum and grain-size histories.Two obvious dry events occurred in 3760 and 2170 cal.a BP,respectively.At 2170 cal.a BP,the water level of the Chaohu Lake reached the lowest as the lakebed possibly exposed. Such lake sediment observations are consistent with the historical records in this area.     

Forcing of wet phases in southeast Africa over the past 17,000 years

Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000?years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000?years ago) and the Younger Dryas (around 12,000?years ago), or when local summer insolation was high in the late Holocene, that is, during the past 4,000?years.     

从陆架泥质沉积中寻找高分辨率的全新世东亚季风记录

当前对全新世东亚季风的研究,一是重造了不同地区的季风气候与环境特点,分析、划分了不同的阶段并总结了各阶段的特点;二是通过高分辨率的气候代用指标进一步开展定量古气候研究,揭示其变化与周期,探讨其驱动机制.已有的研究主要来自陆地,而利用海洋沉积物研究季风则集中在深海;且主要体现的是气候整体变化特征或侧重于夏季风,而专门论述全新世东亚冬季风的报道则较少;尚未在短时间尺度上有效地确定全新世东亚冬、夏季风的关系及其驱动机制.该文指出,可以利用中国边缘海陆架泥质沉积开展全新世高分辨率的东亚古季风研究,其粒度和Rb/Sr比值等元素地球化学指标可分别作为高分辨率的东亚冬、夏季风演化的替代性指标.     

Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model

Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.     

Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean

During the last ice age, the Indian Ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial-scale climate events in the North Atlantic region, suggesting a mechanistic link. In the Holocene epoch, which had a more stable climate, the amplitude of abrupt changes in North Atlantic climate was much smaller, and it has been unclear whether these changes are related to monsoon variability. Here we present a continuous record of centennial-scale monsoon variability throughout the Holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic Arabian Sea. Our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the North Atlantic region--including the most recent climate changes from the Medieval Warm Period to the Little Ice Age and then to the present. We therefore suggest that the link between North Atlantic climate and the Asian monsoon is a persistent aspect of global climate.