晚冰期以来月亮湖孢粉记录反映的古植被与古气候演化

地处季风/非季风影响过渡地带的月亮湖是大兴安岭中段阿尔山-柴河火山区中的一个火山口湖.其长8.86 m的沉积岩心孢粉记录, 揭示了末次冰期晚期以来的古植被演化和古气候变化历史: 20.9~18.0 cal. ka B.P.期间研究区的植被为典型草原, 气候寒冷干旱; 18.0~15.3 cal. ka B.P.期间研究区的植被为草甸草原, 气候寒冷湿润; 15.3~14.0 cal. ka B.P.期间乔木开始在当地发育, 植被开始由草甸草原向森林草原转变, 气候向较为温暖湿润的方向转变; 14.0~12.8 cal. ka B.P.期间森林草原在温暖湿润的气候影响下, 森林扩张, 草原退缩, 与B?lling-Aller?d暖期相对应; 12.8~11.8 cal. ka B.P.期间草原在寒冷气候下扩张, 可与新仙女木期相对应; 11.8~0.8 cal. ka B.P. 期间在较为温暖的气候条件下, 草原在气候快速变冷事件的影响下发生了多次扩张, 其中, 较为明显的6次气温突降事件分别发生在9.0~8.9, 8.2~7.8, 7.0~6.8, 6.1~5.6, 5.4~5.2, 2.3~1.8 cal. ka B.P..这些快速气候变化事件与全球和区域中其他高分辨率古气候记录具有可比性, 揭示出月亮湖敏感地记录了全球和区域气候的变化, 同时也表明研究区的高分辨率孢粉分析是研究东亚季风强度变化的良好指标.      

倒数第二次冰期气候不稳定性的黄土记录

自格陵兰冰芯的氧同位索曲线发表以来,有关“轨道”以下尺度（即千年级）气候变化历史的研究工作,在全球范围内已做了许多。这些工作较为一致地证明,尽管不同区域内短尺度气候变化的特点不一定相互一致,但冰期气候不稳定性现象还是普遍存在的。但是,迄今为止,有关这方面的研究工作主要集中在末次冰期,因此,气候不稳定性是否存在于第四纪的其它冰期尚不得而知。最近,我们对会宁李家源剖面黄土沉积的S。～LZ段落做了详细的采样和粒度分析,样品间距为2cm,粒度分析结果如图l。会宁李家源剖面位于黄土高原西部,S。～S。的总厚度为4…     

新疆艾里克湖炭屑记录的中亚干旱区MIS 3中期以来的古火灾演化

大规模火灾能够对当地植被和生产经济造成不可逆的损害, 严重影响着人们的生产生活。中亚干旱区生态系统脆弱, 火灾频发, 使得该地区成为研究古火灾的理想地区之一。MIS 3时期是距离现今最近的间冰阶, 气候上与现在有许多相似之处, 是进行古气候研究的重要时段。通过对长时间尺度上的火灾演化及其影响因素的了解, 即有助于我们理解火灾对植被和气候变化的响应机制, 又能够为现代预测和治理火灾提供一定的科学依据。本研究以新疆艾里克湖Ailike-2019孔(岩芯长4.49 m)沉积岩芯为研究对象, 通过AMS ¹⁴C测年、花粉通量和炭屑分析, 重建艾里克湖约40 ka以来的古火灾演化序列。结果表明, MIS 3中、晚期(40.2~26.7 cal.ka B.P.), 植被覆盖度较差, 火灾较少; MIS 2时期(26.7~11.7 cal.ka B.P.), 植被覆盖度差, 火灾少; 全新世(11.7 cal.ka B.P. 至今), 植被覆盖度显著上升, 火灾频发。研究区自MIS 3中期以来的火灾活动与植被覆盖度的变化具有相似的趋势, 说明火灾的发生可能与植被覆盖度的变化有关。这与中亚干旱区的其他炭屑记录相似, 表明中亚干旱区轨道尺度上的火灾可能主要受可燃生物量控制。暖湿/冷干的气候条件导致植被覆盖度扩张/缩小, 从而提供了更多/更少的可燃生物量, 使得火灾能够产生大量/少量炭屑。

     

河西走廊末次冰期芒硝和砂楔与古气候重建

芒硝和砂楔是冷干气候环境的典型标志。河西走廊砂楔主要形成在晚更新世冲洪积砾石层中 ,楔体内充填的风成砂14 C年龄证明其是末次冰期的产物 ,古砂楔所对应的年均气温为- 5 6℃左右。芒硝主要分布在内陆河终端的盐湖中 ,花海芒硝矿粘土夹层中的陆生树枝残条普通14 C和AMS14 C年龄分别为 (116 0 0± 2 80 )aB .P .和 (11181± 54)aB .P .,证明芒硝层为末次盛冰期 (LGM )和新仙女木期 (YD)异常冷干气候的产物。计算表明 ,该区LGM年均气温较现在低 11～ 15℃ ,YD年均气温比现代低约 6～ 8℃。这一降温幅度与中国北方根据孢粉、砂楔、冰芯等所推测的气温下降值大体一致 ,亦与最近有关北半球高、中纬度冰期降温幅度的研究相符合     

河西走廊末次冰期砂楔的发现及其古气候意义

河西走廊砂楔主要形成在晚更新世冲洪积砾石层中，楔体内充填的风成砂^14C年龄证明其是末次冰期的产物，在末次冰期，洒西走廊年平均气温为－5－7度左右，较现在低13－15度，这一 估算数据与根据本区芒硝沉积层所推测的气温下降值是一致的，亦与最近有关北半球高，中纬度冰期降温幅度的研究相符合，当时，河西走廊西段年降水量可能达到100－200mm，比现在平均年降水量增加约100mm左右。     

重庆金佛山石笋的同位素年龄和古气候信息

对采自重庆金佛山梁天湾洞穴的一根长达295mm的石笋进行了高精度的TIM S-U系定年和碳氧稳定同位素测试分析,初步建立了末次冰期晚期( 31. 90～15. 21 ka B. P. )以来长江中游地区较高分辨率的古气候变化序列。石笋大约从31.90kaB. P.开始沉积,至15. 21kaB. P.沉积结束,属于末次冰期晚期的产物,其平均沉积速率为1. 77mm /100a。从石笋的氧同位素曲线中明显地检出了Heinrich事件,并且氧同位素曲线与周边地区的石笋记录有着良好的对比关系。      

过去气候演化的阶段性和突变

地球系统的历史信息是评估全球变化的一项重要因素。前些年，过去气候研究中发现了气候的突然变化的现象，突变语气大多出现在冰期，或由冰期向间冰期的过渡时期、并认为这是冰盖的成冰与溶解过程造成海水铅直运动的结果。近些年，过去气候研究还发现在间冰期中也出现突变。我国的历史文献，冰芯和沉积的高分辨率的古气候恢复工作发现近２０００年中国气候明显存在着突变事件。     

西北干旱区石羊河流域末次冰期晚期气候不稳定性记录

通过对我国西北干旱区石羊河流域三角城末次冰期最盛期晚期-晚冰期地层剖面沉积物中有机质碳同位素分析,表明在季风边缘带的沉积地层中较详细地记录了这一时期气候快速颤动,发生千年至百年尺度的冷干-温湿变化,高分辨的有机质碳同位素组成与GRIP氧同位素组成有较好的可比性,表明与全球古气候变化有明显的联系,也反映在末次冰期最盛期与晚冰期过渡期气候温湿,陆地植被比较发育,可能与东亚季风有关。有机质碳同位素这一指标对气候记录较敏感,是重建干旱区高分辨古气候演化模式十分有效的手段,在季风交汇带能灵敏地记录到气候快速变化。     

末次冰期以来中国西南地区火灾活动历史及其对植被生态系统的影响

我国西南地区森林火灾频发, 多与人类活动有关。第四纪地质时期的火灾变化过程及与气候变化和人类活动之间的关系一直是学术界关注的焦点。本研究利用腾冲青海湖(25.1312°N, 98.5731°E)和贵州草海湿地(26.8140°N, 104.3405°E)沉积物岩芯(长度分别为4.6 m和4.05 m), 进行炭屑和孢粉统计分析。在区域数据对比的基础上, 试图重建中国西南地区约25 ka B.P. 以来的火灾变化历史及植被的响应。研究结果表明, 末次冰期(25.0~10.3 ka B.P.)与晚全新世(4.2~0 ka B.P.)时期森林火灾十分活跃, 但两个阶段的火灾对植被的影响差异十分明显。末次冰期阶段(25.0~10.3 ka B.P.)区域内乔木类型以常绿硬叶栎、云杉/冷杉属等为主, 这些地带性植被在末次冰期火灾增强时仍维持主要优势; 而在晚全新世(4.2~0 ka B.P.)火灾增强阶段, 次生林的桤木属、松属等则成为优势种属, 草海记录中禾本科花粉在近2 ka B.P. 以来也达到最大值, 反映出人类活动的影响。高频率火灾导致原来在中全新世的顶级常绿阔叶林遭到反复焚烧, 并难以恢复。通过对比区域火灾和气候记录, 本研究认为西南地区末次冰期的火灾变化主要受控于干冷的气候条件, 尤其是冰期夏季风减弱使区域内降水减少和湿度降低。中全新世时期(9.5~5.0 ka B.P.)季风增强, 降雨充沛, 火灾强度和频率降到最低。这些变化特征与石笋氧同位素基本一致。晚全新世的频繁火灾则与人类活动增强叠加于夏季风减弱有关, 且前者成为引发森林火灾的最主要因素。本研究深入探讨了中国西南地区末次冰期以来火灾强度变化历史及其对植被的影响, 揭示了自然与人为因素的火灾触发机制, 为灾害预测、植物保护及区域规划等提供了新的数据。

     

河西走廊花海剖面晚冰期以来年代学及沉积特征研究

选择位于河西走廊的花海古湖泊沉积剖面作为研究对象,根据13个普通14C和5个AMS14C年代结果,以沉积物岩性特征为主要指标,建立了晚冰期以来花海湖泊沉积的年代框架及环境变化过程.结果表明:花海地区新仙女木期和晚冰期花海湖泊主要以芒硝沉积为主,指示了较低的温度环境.芒硝沉积中的淤泥细线为短暂升温标志,芒硝-淤泥-芒硝的...     

Late Quaternary environmental phases in the Eastern Cape and adjacent Plettenberg Bay-Knysna region and Little Karoo, South Africa

Four major climato-environmental phases have been identified in the Eastern Cape, Plettenberg Bay-Knysna region and Little Karoo between somewhat before ∼40 000 cal. a BP and the present: the Birnam Interstadial from before 40 000 cal. a BP until ∼24 000 cal. a BP; the Bottelnek Stadial (apparently equating with the Last Glacial Maximum) from ∼24 000 cal. a BP until before ∼18 350 cal. a BP; the Aliwal North (apparently equating with the Late Glacial) from before ∼18 350 cal. a BP until ∼11 000 cal. a BP; the Dinorben (apparently equating with the Holocene) from ∼11 000 cal. a BP until the present. The evidence for, and the characteristics of, these phases is briefly described.     

New OSL dating of UK loess: indications of two phases of Late Glacial dust accretion in SE England and climate implications

Windblown dust deposits or loess, locally known in the UK as brickearth, blanket many parts of southern England outside the limits of the British and Irish Ice Sheet. The best‐studied loess exposures occur in Kent, southeast England, where the deposits are believed to be Late Glacial in age. New sedimentological evidence is presented for phases of accretion with two distinct units, a calcareous brickearth exhibiting periglacial cryoturbation and a non‐calcareous, massive brickearth. Optically stimulated luminescence (OSL) dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

Glacial Lake Victoria,a high‐level Antarctic Lake inferred from lacustrine deposits in Victoria Valley

We present evidence of a large lake (Glacial Lake Victoria) that existed in Victoria Valley in the dry valleys region of Antarctica between at least 20 000 and 8600 ¹⁴C yr BP. At its highstands, Glacial Lake Victoria covered 100 km² and was ca. 200 m deep. The chronology for lake‐level changes comes from 87 AMS radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present‐day lakes on the valley floor. The existence of Glacial Lake Victoria, as well as other large lakes in the dry valleys, indicates a climate regime significantly different from that of today at the last glacial maximum and in the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd.     

Stratigraphy and thermoluminescence dating of Late Glacial cover sand in Denmark

In western Jutland deposits with a texture and structure similar to Dutch cover sands have been found. Investigations have been carried out on the lithology and the lithostratigraphic sequences. Pollen analysis is used for biostratigraphic correlation, and ages have been obtained by the radiocarbon method as well as by thermoluminescence techniques using both quartz and eldspar. The five sites are presented separately and the data are integrated into a general stratigraphic outline of the Late Glacial cover-sand sequence in Jutland. During the latest part of the Upper Pleniglacial and the earliest Late Glacial, older cover-sand type was deposited. Locally this sediment was also deposited during the later parts of the Late Glacial. Younger cover-sand type was deposited primarily during the Early Dryas and Late Dryas, but some sand of this type was also laid down during the Allerød and the earliest Holocene. The palaeobotanical records are discontinuous, but plant growth was probably present throughout the Late Glacial; only during the Altered did the deposition of sand decrease long enough to allow a relatively stable vegetational development. The investigation shows that the sequence of events in Jutland is similar to the Dutch record.     

泸沽湖地区晚全新世气候和环境演变

泸沽湖地区受人类活动影响较小、对气候变化较为敏感,是开展古气候研究的理想区域。本文以孢粉为重要研究手段,对采自泸沽湖草海地区103cm的浅钻沉积物开展研究,采样间距2cm,共取得52块样品用于孢粉分析。沉积物年龄采用AMS-~(14)C测定,经校正之后钻孔底部年龄为3455cal.a BP。经实验分析之后,所有样品均含有丰富的孢粉类群,反映的植被组成主要以松(Pinus)林为主,铁杉(Tsuga)也较为常见,被子植物中则以栎属(Quercus)占绝对优势,栗属(Castanea)和木犀科(Oleaceae)植物也频繁出现,而草本植物则以禾本科(Gramineae)为主,蓼科(Polygonaceae)、菊科(Asteraceae)和莎草科(Cyperaceae)植物也是重要的组成成分,林下生长有大量的蕨类的植物,主要以紫萁属(Osmunda)、石松属(Lycopodium)和膜蕨科(Hymenophyllaceae)等为主,另外,采样点草海为季节性湿地,水生植物主要以香蒲属(Typha)和藻类植物中的双星藻(Zygnema)和水绵(Spirogyra)最为常见。为了获得该地区晚全新世以来的气候变化曲线,本研究采用共存分析法分别对划分的四个孢粉带进行了古气候的定量重建,年均温和年均降水量分别为:3455cal.a BP至2585cal.a BP,MAT(mean annual temperature)=11.5~18.6℃,MAP(mean annual precipitation)=797.5~1484.3mm;2585cal.a BP至1699cal.a BP,MAT=11.7~18.6℃,MAP=617.9~1523.1mm;1699cal.a BP至595cal.a BP,MAT=8.5~18.6℃,MAP=797.5~1484.3mm;595cal.a BP至今,MAT=5.7~18.6℃,MAP=617.9~1484.3mm。结果显示该地区3455cal.a BP以来气候经历了略微变暖-变凉-持续变凉-回暖四个阶段。本研究还将变化曲线与其他地区同时代的研究结果进行了对比分析,显示年均温的变化趋势与格陵兰冰芯δ~(18)O以及祁连山敦德冰芯所反映的温度变化趋势基本一致,并可观察到中世纪暖期、晚全新世小冰期及现代温暖期。     

Late Quaternary lake-level changes of Lake El'gygytgyn, NE Siberia

Lake El'gygytgyn is situated in a 3.6 Ma old impact crater in northeastern Siberia. Presented here is a reconstruction of the Quaternary lake-level history as derived from sediment cores from the southern lake shelf. There, a cliff-like bench 10 m below the modern water level has been investigated. Deep-water sediments on the shelf indicate high lake levels during a warm Mid-Pleistocene period. One period with low lake level prior to Marine Oxygen Isotope Stage (MIS) 3 has been identified, followed by a period of high lake level (10 m above present). In the course of MIS 2 the lake level dropped to − 10 m. At the end of MIS 2 the bench was formed and coarse beach sedimentation occurred. Subsequently, the lake level rose rapidly to the Holocene level. Changes in water level are likely linked to climate variability. During relatively temperate periods the lake becomes free of ice in summer. Strong wave actions transport sediment parallel to the coast and towards the outlet, where the material tends to accumulate, resulting in lake level rise. During cold periods the perennial lake ice cover hampers any wave activity and pebble-transport, keeping the outlet open and causing the lake level to drop.     

Evidence for high-frequency late Glacial to mid-Holocene (16,800 to 5500 cal yr B.P.) climate variability from oxygen isotope values of Lough Inchiquin, Ireland

A 7.6-m core recovered from Lough Inchiquin, western Ireland provides evidence for rapid and long-term climate change from the Late Glacial period to the Mid-Holocene. We determined percentage of carbonate, total organic matter, mineralogy, and δ¹⁸O_calcite values to provide the first high-resolution record of climate variability for this period in Ireland. Following deglaciation, rapid climate amelioration preceded large increases in GISP2 δ¹⁸O_ice values by ∼2300 yr. The Oldest Dryas (15,100 to 14,500 cal yr B.P.) Late Glacial event is documented in this record as a decrease in δ¹⁸O_calcite values. Brief warming at ∼12,700 cal yr B.P. was followed by characteristic Younger Dryas cold and dry climate conditions. A rapid increase in δ¹⁸O_calcite values at ∼10,500 cal yr B.P. marked the onset of Boreal warming in western Ireland. The 8200 cal yr B.P. event is represented by a brief cooling in our record. Prior to general warming, a larger and previously undescribed climate anomaly between 7300 and 6700 cal yr B.P. is characterized by low δ¹⁸O_calcite values with high-frequency variability.