洞庭盆地末次冰期中晚期以来黑褐色土壤剖面野火记录及气候关联

洞庭盆地澧阳玉成黑褐色土壤剖面记录了末次冰期中晚期以来火生态的演变过程.通过野外采样和分析测试,参照可靠AMS-14C测年和考古数据断代,利用沉积物中高分辨率炭屑和黑碳数据,探讨该区域末次冰期中晚期以来的野火发生和快速气候变化以及植被演替的相互作用.结果表明:该研究区域氧同位素MIS3(Marine Isotope Stage,56.0~23.0 ka BP)期间,气候冷干向暖干转变,野火发生十分有限;氧同位素MIS2(23.0~10.6 ka BP)阶段,气候冷湿,C_3木本植被明显增加.然而,随着百年-千年尺度气候冷事件发生,冬季风加强和可燃物干燥程度的增加,促使区域和本地野火普遍发生;氧同位素MIS1(10.6~7.0 ka BP)阶段,随着气温和降水的增加,植被由温带落叶阔叶混交林(C_3木本)所取代,致使区域野火明显下降.洞庭盆地野火发生与末次冰期快速突变气候事件(Heinrich and Younger Drays events)密切关联表明千年尺度野火机制模式受到北半球太阳辐射所控制的东亚夏季风强弱和全球冰量变化以及植被演替的共同影响.     

汉江上游归仙河口剖面地球化学特性及其意义

对汉江上游谷地归仙河口剖面的常量元素分布进行研究,结果显示:归仙河口剖面风成黄土的化学成分以SiO2、Al2O3和Fe2O3为主,Ca、Na、Mg、Si相对于K表现为迁移淋失,Fe、Al相对富集,元素的活动性及迁移序列为CaNaMgSiKAlFe,Ca、Na、K的迁移特征说明其达到中等风化阶段.化学蚀变指数、K2O/Na2O、SiO2/Al2O3、(CaO+K2O+Na2O)/Al2O3和(Al2O3+Fe2O3)/(MgO+CaO+Na2O)等地球化学参数,说明古土壤S0形成时期的化学风化最强烈,黄土L1、Lt和L0形成时期的风化作用相对较弱;揭示汉江一级阶地抬升(18.0ka B.P.前后)以来气候干冷,11.5ka B.P.开始气候转向暖湿,8.5ka B.P.开始气候最为暖湿,3.0ka B.P.开始气候骤然恶化;并记录到4次洪水事件,分别发生在12.5~12.4ka B.P.、7.5~7.0ka B.P.、3.1~3.0ka B.P.和1.0~0.9ka B.P.期间.     

贵州荔波42.0kaB.P.~65.0kaB.P.气候变化的石笋记录

对贵州荔波董哥洞D42石笋进行TIMS-U测年和碳、氧同位素分析,建立末次冰期42．0ka B．P．～65．0ka B．P．的古气候变化时间序列。研究结果表明,荔波地区在65．0ka B．P．～42．0ka B．P．石笋记录的冷暖事件所反映出的季风气候变化,大致可分为3个气候阶段;65．0ka B．P．～60．6ka B．P．相当于海洋氧同位素MIS4晚期,反映本阶段东亚冬季风强盛,气温降低,表现为干旱寒冷的气候环境;60．6ka B．P．～48．4ka B．P．相当于海洋氧同位素MIS3早期,反映东亚夏季风相对增强,气温升高,有效降水相对较少,表现为温暖半干旱的气候环境;48．4ka B．P．～42．0ka B．P．相当于海洋氧同位素MIS3中期,显示东亚夏季风由强变弱,东亚冬季风相对增强,表现为干旱冷凉的气候环境。石笋记录揭示的2次寒冷事件在各类沉积物中均有记录,反映为全球变化的气候事件,相当于北大西洋沉积物中的Heinrich5和Heinrich 6冷事件,可以进行全球对比,显示荔波地区与北极地区存在着古气候的遥相关。     

三门峡王官与武威沙沟黄土记录中的末次间冰期向末次冰期转换期的暖性回返事件

河南三门峡王官剖面与甘肃武威沙沟剖面捕捉到了末次间冰期向末次冰期转换时期发生于72 ka前后持续时间约为2 ka的一暖性回返事件,两剖面的冬、夏季风替代指标对该暖性回返事件的反应在时间上大致同步(其时间段约为71～73 ka,在71.4～72.1 ka前后该暖性回返事件最强盛),暗示该暖性回返事件在东亚季风区可能是一普遍存在的气候突变事件.鉴于该暖性回返事件在全球其他地区的海洋、陆地、冰芯记录中也有较普遍的反映,我们认为该事件很可能是一次发生于气候转型期的全球普遍存在的暖性突变事件.     

长江万州-巫山段阶地成因

根据长江万州-巫山段的阶地类型、沉积物特征和形成时代,结合青藏高原间歇性构造隆升过程、深海氧同位素变化曲线和青藏高原冰期-间冰期旋回,探讨730 ka B.P.以来万州-巫山段河流阶地的成因.研究表明,河流阶地不同阶段的下切速率响应了青藏高原的2期构造隆升事件:昆黄运动、共和运动.在与深海氧同位素气候周期旋回的比较中发现,阶地主要在冰期发生堆积,研究区T3、T2、T1阶地堆积期主要集中在MIS5d、MIS3b和YD冷期;下切期响应了共和运动的构造抬升过程.T4阶地主要发育于深海氧同位素MIS12阶段及青藏高原聂聂雄拉冰期,沉积物特征与同期珠穆朗玛峰北坡海洋型冰川具有相似的气候背景,表明T4阶地堆积期主要受控于气候变化.T5阶地的发育响应了重要构造运动——昆黄运动的构造抬升,下切至基岩;MIS18-MIS17气候转换期的不稳定性促进了河流的下切.构造运动、气候变化是万州-巫山段阶地形成演化的主要原因,并在对不同阶地的堆积-下切发育阶段的影响上具有相似性和差异性.     

萨拉乌苏河流域全新世气候变化的元素地球化学记录

通过对萨拉乌苏河流域滴哨沟湾左岸沉积剖面常量元素Si、Al、Fe、Ca、Mg、K、Na含量及其比值变化的分析,结合~(14)C测年结果及粒度、有机质指标,并综合已有研究,探讨了该地区全新世以来的气候变化.研究表明,9.6ka BP前气候干冷,沉积相为风成沉积;9.6~8.4ka BP气候由干冷向暖湿转变,期间存在干冷波动;8.4~4.0ka BP进入全新世大暖期,其中,8.4~6.5ka BP为全新世大暖期的鼎盛时期,降水增加,积水成湖,湖泊水位高且稳定;6.5ka BP气候发生明显转变;6.5~4.0ka BP湖泊水位逐步下降形成富含螺壳的浅水环境,但气候整体仍较为湿润;4.0~1.2ka BP气候变干冷,发育沼泽;1.2~0.7ka BP气候转暖湿,沉积相由沼泽相转变为湖泊相;0.7~0.5ka BP为河流相沉积,气候较为干冷.剖面记录的气候变化可与东亚季风变化、温度变化、太阳辐射进行对比,反映了该区域气候变化与全球气候变化的一致性.     

粤北锦江扶溪段河流阶地的光释光测年

南岭是我国重要的自然地理分界线和东亚季风环流屏障，第四纪期间粤北山地发育的多级河流阶地是研究南岭构造运动与气候变化的良好地质载体。粤北锦江扶溪段保留了5级阶地，运用光释光（OSL）技术对T2到T5级阶地的砾石层进行了测年，并从气候和构造角度分析了阶地成因。结果显示:T3形成于67 ka，对应于深海氧同位素的MIS4阶段；T2形成于51 ka，对应于MIS3b阶段；阶地沉积层堆积于冷期，气候变化影响着河流的侧蚀、堆积和下切作用交替进行，而新构造运动的构造抬升发动了足够的下切量使锦江扶溪段依次下切17 m、19 m、12 m和10 m形成T5、T4、T3和T2；南岸的河谷下切速率为0.3 mm/a，大于2倍的流域现代侵蚀速率，地貌发育符合年轻山地的抬升-下切-侵蚀模式。     

云南小中甸盆地地球化学特征及其环境意义

通过对云南小中甸盆地湖相沉积物地球化学元素特征及其相关元素比值的分析,结合14C年代测定,重建了小中甸盆地40cal.ka BP以来的环境变化过程.研究发现:小中甸湖相沉积物中氧化物含量表现出SiO2Al2O3Fe2O3CaOMgOK2OTiO2Na2O的特征,Na2O/Al2O3值分布范围较为集中,且相对于上地壳有较明显的亏损.小中甸沉积物地球化学记录了多次湖泊水位波动,以及千年尺度的气候变化过程,其表现为暖干-冷湿-暖干的变化特征,并指示了40cal.ka BP以来西南季风演化的历史,其研究结果可与中甸纳帕海和鹤庆盆地进行对比.对云南小中甸盆地湖相沉积物地球化学的研究有助于重建西南季风的演化过程以及区域环境气候与全球变化耦合机制的进一步探究.     

青藏邛多江盆地40.4~30.0 cal ka BP湖相沉积物粒度特征及其古气候意义

对青藏邛多江盆地一段连续沉积剖面4个湖相沉积物样品进行AMS14C测年,得到此剖面的顶底年龄分别为30.0 cal ka BP和40.4 cal ka BP。并分析沉积物粒度的平均粒径(M_z)、中值粒径(M_d)、标准偏差(σ_1)、分选系数、频率分布曲线等,将研究区的古气候演变划分为5个阶段:阶段Ⅰ(40.4~38.5 cal ka BP)气候湿润期、阶段Ⅱ(38.5~35.4 cal ka BP)气候干旱期、阶段Ⅲ(35.4~32.4 cal ka BP)气候湿润期、阶段Ⅳ(32.4~31.7 cal ka BP)气候动荡期、阶段Ⅴ(31.7~30.0 cal ka BP)气候转干期。对比发现,粒度曲线与格陵兰冰芯氧同位素曲线有较好的响应,而且发现40.4~30.0 cal ka BP时期邛多江盆地有两次显著的气候事件:39.4 cal ka BP短暂干旱事件和35 cal ka BP强降水事件,而粒度均值曲线与格陵兰冰芯氧同位素曲线的差异,可能与特强夏季风有关。     

S2以来下蜀黄土沉积序列磁化率记录与深海氧同位素记录的对比

对镇江下蜀黄土剖面进行了系统的磁化率测试,并同深海氧同位素记录进行了对比。结果表明,S2以来下蜀黄土磁化率记录与深海氧同位素记录存在良好的对应关系。首次在下蜀黄土记录中发现了相当于深海氧同位素5a,5b,5c,5d和5e亚阶段的波动特征;下蜀黄土S2磁化率记录则可与深海氧同位素7阶段进行细节上的详细对比。对比揭示,最近20多万年以来,下蜀黄土堆积区对全球古气候变化有着积极的响应;同时,下蜀黄土记录的古气候变化在某些阶段又具有明显的区域特征,可能反映的是全球气候变化效应与东亚古季风气候影响的叠加作用。镇江下蜀黄土剖面能获得精度较高的全球变化信息与其特定的地理位置、纬度位置和地貌条件有关。     

Orbital- and millennial-scale variability of the Asian monsoon during MIS8 from Sanbao Cave at Mount Shennongjia,central China

One stalagmite oxygen isotope record from Sanbao Cave, China, established with 7 230Th ages and 355 oxygen isotope data, pro- vides a continuous history of the East Asian Monsoon (EAM) intensity for the period from 284 to 240 thousand years before present (ka BP) with typical errors of 3―4 ka. This new record extends the previously published stalagmite δ18O record back to the marine oxygen isotope stage (MIS) 8. The MIS8 EAM record broadly follows orbitally-induced insolation variations and is punctuated by...     

Simulation of the future change of East Asian monsoon climate using the IPCC SRES A2 and B2 scenarios

In this paper, we applied the newest emission scenarios of the sulfur and greenhouse gases, i.e. Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 and B2 scenarios, to investigating the change of the East Asian climate in the last three decades of the 21st century with an atmosphere-ocean coupled general circulation model. The global warming enlarges the land-sea thermal contrast and, hence, enhances (reduces) the East Asian summer (winter) monsoon circulation. The precipitation from the Yangtze and Huaihe river valley to North China increases significantly. In particular, the strong rainfall increase over North China implies that the East Asian rainy area would expand northward. In addition, from the southeastern coastal area to North China, the rainfall would increase significantly in September, implying that the rainy period of the East Asian monsoon would be prolonged about one month. In July, August and September, the interannual variability of the precipitation enhances evidently over North China, meaning a risk of flooding in the future.     

Stalagmite-inferred Holocene precipitation in northern Guizhou Province,China, and asynchronous termination of the Climatic Optimum in the Asian monsoon territory

An absolute-dated, bi-decadal-resolution, stalagmite oxygen-isotopic time series from Shigao Cave reveals the evolution of summer monsoon precipitation over the past 9.9 ka BP in northern Guizhou Province, Southwest China. The  18O-inferred climate conditions are divisible into three distinct stages: (1) a maximum humid era from 9.9-6.6 ka BP; (2) a gradual declining precipitation interval between 6.6-1.6 ka BP; and (3) a relatively low precipitation time window after 1.6 ka BP. Consistency of contemporaneous stalagmite Holocene 18O records between Shigao and other caves in the Indian and East Asian monsoon realms support the effect of primary orbital solar forcings on monsoonal precipitation. However, statistical analysis shows a significant spatial asynchroneity of the Holocene Optimum termination in the Asian monsoon territory. The Holocene Optimum ended at 7.2-7.4 ka BP in Oman, located in the Indian monsoon region, and at 5.6-5.8 ka BP in Central China, in the East Asian monsoon zone. In Southwest China, the termination occurred between these periods, at 6.6-7.0 ka BP, and was influenced by both monsoon systems. We propose that this spatially asynchronous ending of Holocene Optimum in Asia may be attributed to sea surface temperature changes in the western tropical Pacific, which is a primary moisture source for the East Asian monsoon.     

面临2000年后全球气温和海面升高的挑战——第四纪气候研究的一项紧要任务

本文论证我国东部第四纪气候变化特征。由于青藏高原的强烈隆起,我国东部于冰期中气候极端干燥而严寒;间冰期及全新世新高温时期,我国华北及内蒙部分地区气温与降水均高于今日。当大气中C_2O倍增时,据GCMs,北半球中伟地带将趋向干燥,美国中西部平原、气温升高,土壤湿度低降,气候干早。本文据我国前一间冰期及全新世新高温时代的气候图象,与太平洋彼岸的下一世纪图象有显著差异。本文运用EOF's函数分析方法研究我国相对海面上升率为3mm/年。由于温室效应引起21世纪气温升高,对我国农作物产量有其有利的一面,而沿海新构造下沉平原区,可能招致严重灾害,应引起我国经济建设决策上的重视,及时作出相应措施。     

Abrupt climate change of EastAsian Monsoon at 130 kaBP inferred from a high resolu-tion stalagmite δ18O record

^230Th ages and oxygen isotope data of a stalagmite from Shanbao Cave in Hubei Province characterize the East Asian Monsoon precipitation from 133 to 127ka. The decadal-scale high-resolution δ^18O record reveals a detailed transitional process from the Penultimate Glaciation to the Last Interglaciation. As established with ^230Th dates, the age of the Termination Ⅱ is determined to be 129.5±1.0 kaBP, which supports the Northern Hemisphere insolation as the triggers for the ice-age cycles. In our δ^18O record, the glacial/interglacial fluctuation reaches about 4‰, almost the same level as in other Asian Monsoon cave stalagmite δ^18O records. The transition of the glacial/interglacial period in our record can be recognized as four stepwise stages, among which, a rapid rise of monsoon precipitation follows the stage of “Termination Ⅱ pause”. The rapid rise is synchronous with the abrupt change of global methane concentration, which reflects that an increase in both Asian Monsoon precipitation and tropical wetland plays an important role in the global climate changes.     

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 …     

川东北宋家洞石笋氧碳同位素及锶含量突变分析

通过对宋家洞石笋SJ3的氧碳同位素及锶含量进行Mann-Kendall test突变分析,得出以下结论:(1)氧同位素值记录了末次冰盛期向Heinrich Event 1时期的转变;(2)碳同位素值和锶含量记录了由H1冷期向BФlling-AllerФd暖期的转变;(3)碳同位素值和锶含量指示了在19.8～15.3ka时当地的东亚夏季风和冬季风呈正相关关系,在15.3～14.8 ka呈负相关关系,表明石笋SJ3记录了古气候环境的冷干、暖湿变化,且不同气候指标对环境变化的敏感度不同。     

Comparison of paleoclimatic characteristics between monsoon and westerly areas, China

For past decades there have been many studies on the climate features during the last interglacial and glacial periods. A comparison between the loess record of western China with that of monsoon areas shows some regional differences. ( i) Generally, the climate of the Yili region since the late Pleistocene was dry, with fluctuations. Late Pleistocene climate change in the study area can be divided into 5 stages, corresponding to 5 marine isotopic stages (MIS 1-MISS), (ii) Evidence from grain size composition, magnetic susceptibility, carbonate content, pollen assemblage and geochemistry shows that the climate during the last glacial period was instable. During MIS4 the westerly winds were strong and the humidity was relatively high. Compared with the early stage, MIS2 was dry. In MIS3, westerly winds were relatively weak; pedogenesis prevailed, forming paleo-sols. (iii) In contrast to the Loess Plateau the deposition rate of dust at the early stage was higher than at the late stage of the last galical in the Yili region. The strongest wind event occurred at about 24 kaBP instead of 18 kaBP. (iv) Variations in the grain size indicate that the westerly winds decreased since the deglaciation, but dust accumulation continued until the late Holocene. High carbonate contents, low ratio of Rb/Sr and lack of soil development imply that the climate was dry during the early and middle Holocene. Since the late Holocene the climate became relatively wet and the soil was developed.     

A 60 000-year loess-paleosol record of millennial-scale summer monsoon instability from Lanzhou, China

The 28-m high-resolution Shajinping loess section in Lanzhou on the Chinese western Loess Plateau records a detailed history of millennial Asian summer monsoon change since the earlier last glaciation. Summer monsoon proxies of soil magnetic susceptibility, carbonate content and soil color show that Asian summer monsoon experienced a series of rapid episodic pulse enhancements spanning only ca. 1-2 ka and have sub-Milankovitch cycles of progressive weakening in low frequency domain since ca. 60 kaBP. Soil formation responds to these by deepening colors, accumulating organic matter, increasing biological channels and leaching certain carbonates. The pedogenic degree generally increases with the degree of enhancement of summer monsoon. These may reflect the impact of the last glacial fast climatic change in the North Atlantic region on Asian summer monsoon.