Three modes of climate change since the Last Glacial Maximum in arid and semi-arid regions of the Asian continent

The westerly winds and East Asian summer monsoon play a leading role in climate change of southwestern North America and eastern Asia since the Last Glacial Maximum(LGM),respectively.Their convergence in arid and semi-arid regions of the Asian continent(AAC) makes the regional climate change more complicated on the millennial-scale.There are still limitations in applying paleoclimate records and climate simulations of characteristic periods to investigate climate change patterns since the LGM in this region.In this study,we adopt two indexes indicating effective moisture and rely on a continuous simulation,a time slice simulation,and numerous paleoclimate records to comprehensively investigate the cli-mate change modes and their driving mechanisms since the LGM in AAC.Results demon-strate a millennial-scale climate differentiation phenomenon and three climate change modes possibly occurring in AAC since the LGM.The western AAC largely controlled by the westerly winds is featured as wet climates during the LGM but relatively dry climates during the mid-Holocene (MH),coinciding with the climate change mode in southwestern North America.Conversely,dry conditions during the LGM and relatively wet conditions during the MH are reflected in eastern AAC governed by the East Asian summer monsoon,which leans to the climate change mode in eastern Asia.If climate change in central AAC is forced by the in-teraction of two circulations,it expresses wet conditions in both the LGM and MH,tending to a combination of the southwestern North American and eastern Asian modes.Precipitation and evaporation exert different intensities in influencing three climate modes of different periods.Furthermore,we identify the significant driving effects of greenhouse gases and ice sheets on westerly-dominated zones of AAC,while orbit-driven insolation on monsoon-dominated zones of AAC.     

Tessellons,topography, and glaciations on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau has developed into a vast fortress-like structure that has recently presented a barrier limiting the egress of moisture-bearing air masses. Lower sea levels also affected the climate. This paper examines their effects on the current evidence for the timing of past glaciations, and the development and evolution of permafrost. There are two theories regarding glaciation on the Qinghai-Tibet Plateau(QTP). Kuhle suggested that there was a major, unified ice-cap during the Last Glacial Maximum(LGM), whereas major Chinese glaciologists and others have not found or verified reliable evidence for this per se. There have been limited glaciations during the last 1.1 Ma B.P. but with increasing dominance of permafrost including both primary and secondary tessellons infilled with rock, sand or loess. The East Asia Monsoon was absent in this area during the main LGM, starting at 30 ka B.P. on the plateau, with sufficient precipitation reappearing about 19 ka B.P. to produce ice-wedges. A weak Megathermal event took place between 8.5 and 6.0 ka B.P., followed by Neoglacial events exhibiting peak cold at 5.3–4.7 ka, 3.1–1.5 ka, and the Little Ice Age(LIA) after 0.7 ka. Subsequently,mean annual air temperature has increased by 4 °C.     

中国第四纪冰川作用与深海氧同位素阶段的对比和厘定

随着冰期(阶)与间冰期(阶)旋回的不断细化,第四纪冰期系列与深海氧同位素阶段(MIS)对比之间所反映的问题开始逐步显现。通过中国第四纪冰期与MIS阶段对比,结合分析气候旋回与构造运动对地貌演化的控制作用,研究表明:①冰期(阶)或者间冰期(阶)发生的时段应尽可能对应于MIS的偶数或奇数阶段,有助于MIS框架下新的冰期(阶)的发现;②中更新世以来,中国第四纪冰期-间冰期旋回可能受控于100 ka轨道偏心率变化的气候大背景,昆仑冰期-倒数第二次冰期的冰川规模总体上与全球冰量变化一致。然而,末次冰期早、中期的冰川规模却与MIS所记录的全球冰量变化不尽一致,强烈显示气候与构造环境对冰川作用的影响;③目前在中国第四纪冰期划分方案中,存在着冰期系列由时间和地点双重命名的现象,建议用大理冰期、古乡冰期分别代替末次冰期和倒数第二次冰期。     

伶仃洋ZK19孔晚第四纪沉积地球化学特征 及其古环境意义

依据对珠江口伶仃洋海域ZK19孔岩芯材料的沉积学、年代学和沉积地球化学研究,探讨了该海域古环境演变特征。该孔以末次盛冰期风化层为界,存在2个沉积旋回和2次海侵事件。微量元素质量分数、主量元素（Al2O3/Na2O值、MgO/Al2O3值、Sr/Ba值及V/Cr值等）,化学蚀变指数（CIA）和化学风化指数（CIW）的变化特征,反映了MIS4晚期至MIS3初期,该地由陆相向滨海相过渡,气候从偏冷逐渐升温,海平面逐渐上升,但速度较慢;MIS3该地为河口湾相,气候进一步转暖,海平面以较大幅度上升;MIS2阶段（末次盛冰期）海平面大幅下降,气候变冷;MIS1的8―12 cal. ka B.P.气候逐渐转暖,海平面快速上升,为河流相―滨海潮滩相―河口湾浅滩相―河口湾相;中全新世大暖期,受水下滩槽地貌侧向迁移影响,该孔地层遭剥蚀;晚全新世3 cal. ka B.P.以来,气候整体相对稳定,较早全新世温暖,沉积环境依次为河口湾相―三角洲前缘斜坡相―三角洲前缘浅滩相。     

220 ka以来萨拉乌苏河流域地层磁化率与气候变化

 萨拉乌苏河流域滴哨沟湾剖面磁化率变化结果表明:近220 ka来我国北方气候变化极不稳定,存在着不同尺度的频繁变化,特别是寒冷气候阶段变化尤为频繁,其中倒数第二次冰期存在5个气候旋回,末次冰期存在10个气候旋回。这些气候变化与深海氧同位素、极地冰芯反映的全球变化具有良好的对应关系,反映了该区气候变化与全球变化的一致性。控制本区气候变化的主要因素是全球冰量变化及太阳辐射影响的东亚季风变化。     

基于石笋记录的云贵高原古气候变化研究进展

重建古气候、古环境已成为当今全球变化研究的热点.石笋作为岩溶洞穴次生化学沉积物的典型代表,是古气候研究的重要载体.基于近年来已报道的贵州荔波、茂兰、都匀凯口及云南寻甸、宣威、宁蒗等地11个洞穴30余根石笋的氧同位素数据的综合分析,认识云贵高原163 kaBP以来的古气候变化情况.结果表明,163kaBP以来,青藏高原隆升对全球气候格局的改变及季风系统的形成起到重大影响,在此大背景下,云贵高原气候演变体现了全球一致性,也呈现出其自身规律：（1）倒数第2次冰期的冰盛期（163.3～ 129.28 kaBP）,气候严寒干冷,期间伴随温凉向冷干的转变;（2）末次间冰期（129.28～78.92 kaBP）,气候温暖湿润,但期间冷暖波动变化幅度很大;（3）末次冰期（78.92～11.2 kaBP）,气候极不稳定,冷暖波动很大,总体呈现降雨由多变少,气温由高变低的变化趋势;（4）全新世（11.2 kaBP至今）,气候温暖,雨量充沛,气候呈现变暖—高温—稍变冷—恢复的变化趋势.云贵高原作为一个特殊区域,即东亚季风与印度季风的过渡带,对研究中国甚至于全球季风系统的演变发展有着重要意义.通过多指标多手段,提高研究区研究精度,拟建古气候变化曲线,应对全球变暖的区域性实证研究及未来气候模拟预测将是今后努力的方向.     

Paleoecology of The Southern Chilean Lake District-Isla Grande de Chiloé During Middle–late Llanquihue Glaciation and Deglaciation

Subantarctic Parkland and Subantarctic–North Patagonian Evergreen Forest, embracing >40,000 ¹⁴ C years of middle and late Llanquihue glaciation, are reconstructed from pollen contained in multiple interdrift deposits and cores of lake sediments. The subantarctic plant communities at low elevations have since been replaced by temperate Valdivian Evergreen Forest. Data in support of the vegetation reconstruction derive from close-interval sampling (>1400 pollen analysed stratigraphic levels) and high-resolution chronology (>200 AMS and conventional radiocarbon-dated horizons). Pollen sequences are from 15 sites, eight of which are exposures and seven mires, located in relation to lobes of piedmont glaciers that occupied Lago Llanquihue, Seno Reloncav', Golfo de Ancud, and the east-central sector of Isla Grande de Chiloí at the northern limit of the Golfo Corcovado lobe. Recurring episodes of grass maxima representing Subantarctic Parkland, when grass and scrub became widespread among patches of southern beech (Nothofagus), bear a relationship to glacial advances. The implication of the maxima, prominent with advances at 22,400 and 14,800 ¹⁴C yr BP during late Llanquihue glaciation in marine oxygen-isotope Stage 2, is of successive intervals of cold climate with summer temperatures estimated at 6–8°C below the modern mean. The earliest recorded maximum at >50,000 ¹⁴C yr BP is possibly during late Stage 4. At the time of middle Llanquihue glaciation in Stage 3, cool, humid interstades on Isla Grande de Chiloé with Subantarctic Evergreen Forest, which under progressive cooling after 47,000 ¹⁴C yr BP was increasingly replaced by parkland. During stepwise deglaciation, when transitional beech woodland communities supplanting parkland became diversified by formation of thermophilous North Patagonian Evergreen Forest, warming in the order of 5–6°C was abrupt after 14,000 ¹⁴C yr BP . Closed-canopy North Patagonian Evergreen Forest was established by 12,500 ¹⁴C yr BP . Later, after c. 12,000 until 10,000 ¹⁴C yr BP , depending on location, forest at low elevations became modified by expansion of a cold-tolerant element indicative of ≥2–3°C cooler climate. This stepwise climatic sequence is seen at all late-glacial sites. Cool, humid interstadial conditions, punctuated by cold stadial climate, are characteristic of the last ≥40,000 ¹⁴C years of the Pleistocene at midlatitude in the Southern Hemisphere. Pollen sequences from southern South America and terrestrial–marine records from the New Zealand–Tasmania sector express a broad measure of synchrony of vegetational/climatic change for marine oxygen-isotope Stages 2–3. The data, combined with the timing of glacial maxima in the Southern Andes, Southern Alps of New Zealand, and in the Northern Hemisphere, are indicative of synchronous, millennial-scale, midlatitude climatic changes in the polar hemispheres.     

Signatures of tectonic‐climatic interaction during the Late Cenozoic orogenesis along the northern Chinese Tian Shan

The Chinese Tian Shan is one of the most actively growing orogenic ranges in Central Asia. The Late Miocene‐Quaternary landscape evolution of northern Tian Shan has been significantly driven by the interaction between tectonic deformations and climate change, further modulated by the erosion of the upstream bedrocks and deposition into the downstream basins. In this study, only the accessible Kuitun River drainage basin in northern Tian Shan was considered, and detrital zircon geochronology and heavy minerals were analyzed to investigate the signature of the driving forces for Miocene sedimentation in northern Tian Shan. This study first confirmed a previously recognized tectonic uplift at ca. 7.0 Ma and further revealed that the basin sediments were mainly derived from the present glacier‐covered ridge‐crest regions during 3.3–2.5 Ma. It is suggested Late‐Pliocene to Early Pleistocene sedimentation was likely a response to the onset of the northern hemispheric glaciation. Although complicated, this study highlights that the tectonic‐climatic interaction during the Late Cenozoic orogenesis can be discriminated in the northern Chinese Tian Shan.     

PERSPECTIVE ON CLIMATE CHANGE IN NORTH AMERICA DURING THE TWENTIETH CENTURY

The climate record from many parts of North America provides ample evidence of climate change. For specific elements such as temperature or precipitation, a substantial portion of these changes can be shown to be statistically significant; that is, they either reflect an unusual combination of events in a stationary process or they reflect a nonstationary process. The practical significance of a climate change, however, even when it can be shown to be statistically significant, cannot be assumed. Conversely, it is entirely possible to have a practically significant climate change without statistical significance, although this is less likely to occur.

The preponderance of evidence over recent years suggests that any notion regarding static climate regimes must be dismissed in favor of a dynamic system. The differential heating of our planet which results in a restless atmosphere can also yield a restless climate. Whether this dynamic climate system is merely a manifestation of natural variations or at least partly caused by changes in external influences, we cannot yet be certain. The fact that the climate has changed in North America during the 20th century, and in all likelihood will probably continue to do so in the future, should be considered in any decision-making process related to climate. [Key words: climatic change.]     

Geomorphic and Climatic Implications of Relict Openwork Block Accumulations Near Thabana-Ntlenyana, Lesotho

Conflicting reports appear in the literature from geomorphic studies describing the colder Late Pleistocene environmental conditions of the Lesotho Highlands in southern Africa. Evidence is given for limited glaciation and/or periglacial conditions, with or without permafrost. An investigation of the distribution, morphometric attributes and surface weathering characteristics of relict openwork block accumulations in the area around Thabana‐Ntlenyana, the highest summit in the range, supports the contention for a relatively arid periglacial environment during the Last Glacial period. A phase of enhanced block production is evident from the concentration of blocks in the upper layer of colluvium. Slope mobility on south‐facing slopes is shown in the blockfield fabrics and the increase in downslope relative age of block surfaces. Block production and slope creep are attributed to depressed temperature conditions and seasonal freeze. Colluvium, within which blocks have been incorporated and superimposed, indicates that slope mantles predate the onset of the colder period and evidence militates against either deep snow cover or localised glaciation of south‐facing slopes.     

An early Holocene erosion phase on the loess tablelands in the southern Loess Plateau of China

A Holocene loess profile to the west of Xi'an China was studied multi-disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change. The proxy data obtained from this aeolian loess and palaeosol sequence indicate large-scale variations of climate in the southern Loess Plateau since the last glaciation. A rainwash bed, indicative of a wetter climate, excessive runoff and erosion on the loess tablelands, was identified relating to the early Holocene before the onset of the “climatic optimum”. This is synchronous with the early Holocene physiographic erosional stage identified in the valleys in North China. It means that severe erosion took place when the region was undergoing climatic amelioration during the early Holocene. The evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern Loess Plateau. During the last glaciation, prior to the erosion phase, the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation. Relatively slow dust accumulation and intensive bio-pedogenesis responding to the Holocene “climatic optimum” followed the erosion phase. The loess tablelands were most vulnerable to erosion during the large-scale monsoonal climatic shift from dry-cold glacial to humid-warm post-glacial conditions in the southern Loess Plateau.     

滴哨沟湾地层沉积特征记录的毛乌素沙漠变迁

毛乌素沙漠的盛衰变化明显地受到全球变化特别是东亚夏季风变化的影响。根据毛乌素沙漠东南缘萨拉乌苏河流域滴哨沟湾地层沉积物的物质组成、粒度参数等,结合孢粉研究结果,将沙漠演化过程划分为若干阶段：中更新世晚期沙漠萎缩期,气候温暖半干旱-半湿润,沙漠缩小,为森林草原或灌丛草原;中更新世晚期沙漠稳定期,气候在寒冷干旱-半干旱间波动频繁,自然景观在荒漠、荒漠草原与干草原间变化,并有河流和小湖存在;晚更新世早期沙漠固定期,气候温暖半湿润至半干旱,期间自然景观经历了森林草原、灌丛草原、草原、荒漠草原多种变化;晚更新世晚期沙漠扩张期,气候干旱寒冷,自然景观以荒漠和荒漠草原为主,同时也有草原乃至灌丛草原出现;全新世沙漠频繁变化期,气候变化频繁,沙漠出现多次盛衰变化,自然景观在荒漠、荒漠草原、草原、疏林草原间变化。     

HEMIARID BASIN RESPONSES TO ABRUPT CLIMATIC CHANGE: PALEOLAKES OF THE TRANS-PECOS CLOSED BASIN

Western North American hemiarid basins situated along a climate boundary zone, or threshold, that separates regions of different climate regimes exhibit greater variability to changes in hydroclimatic variables. The Trans-Pecos Closed Basin study examines how global paleoclimatic factors and intrinsic geographic controls act in determining the threshold between states of hydroclimatic equilibria. Geomorphic, radiocarbon, and limnetic evidence identifies four major highstands for late Pleistocene Lake King during the Last Glacial Maximum (LGM). Patterns in the resulting model limnograph for Lake King suggest that runoff contributions from basin catchments to the inundated area were limited by precipitation rather than evaporation. Timing of the onset of lacustrine transgressive events corresponds with the later stages of cooling events recorded in the Greenland ice and North Atlantic deep-sea sedimentary record. Correlation of Trans-Pecos lacustrine environments with North Atlantic cooling implies that full pluvial conditions in the basin were limited to those periods when those cooling events resulted in extreme equatorward shifts of the LGM subpolar winter storm tracks, providing a moisture source to the basin. By comparing timing, intensity, and direction of climate change over a widely spaced array of hemiarid basins, the global implications of climatic events are better understood. [Key words: Last Glacial Maximum, paleolakes, Pleistocene, Trans-Pecos Closed Basin, New Mexico, Texas.]     

华北平原中部晚上新世以来沉积物碳氧同位素特征及其古环境意义

利用华北平原中部衡水水文地质科研深孔的岩芯,对平原区古土壤钙结核层碳氧同位素组分的古气候环境意义及相关气候指标的定量转换进行探讨,发现碳氧同位素对古气候变化具有较好的响应关系:3.5MaB.P.以来华北平原古气候逐渐由湿润转向干旱,早更新世由多个干湿冷暖旋回组成,晚期气候由暖迅速转凉;中更新世气候略温和,由3个冷干-暖湿旋回组成;晚更新世气候变化趋势为湿润-干燥-湿润,总体上呈现增温趋势。进入全新世后,δ13C平均值(-5)较低,属于相对湿润期;δ18 O平均值(-9.5)较低,属于相对寒冷期。应用相关公式可以定量恢复古温度变化,但平原区古土壤层受后期地下水作用的影响较大,如何消除这一影响还需更多数据支持。     

The decreasing spring frost risks during the flowering period for woody plants in temperate area of eastern China over past 50 years

The temperate monsoon area of China is an important agricultural region but late spring frosts have frequently caused significant damage to plants there. Based on phenological data derived from the Chinese Phenological Observation Network （CPON）, corresponding meteorological data from 12 study sites and phenological modeling, changes in flowering times of multiple woody plants and the frequency of frost occurrence were analyzed. Through these analyses, frost risk during the flowering period at each site was estimated. Results of these estimates suggested that first flowering dates （FFD） in the study area advanced significantly from 1963 to 2009 at an average rate of -1.52 days/decade in North-east China （P〈0.01） and -2.22 days/decade （P〈0.01） in North China. Over the same period, the number of frost days in spring decreased and the last frost days advanced across the study area. Considering both flowering phenology and occurrence of frost, the frost risk index, which measures the percentage of species exposed to frost during the flowering period in spring, exhibited a decreasing trend of -0.37% per decade （insignificant） in Northeast China and -1.80% per decade （P〈0.01） in North China, implying that frost risk has reduced over the past half century. These conclusions provide important information to agriculture and forest managers in devising frost protection schemes in the region.     

北半球春季植被NDVI对温度变化响应的区域差异

利用1982年到2000年的探路者NDVI资料，采用奇异值分解分析方法，研究北半球春季NDVI对温度变化响应的空间差异，前7对模态对总的协方差平方的解释率高达91％以上，反映出NDVI和气温的相关性非常高，第一对模态解释率达42．6％，显示北半球最显著的NDVI响应中心在西西伯利亚，其次是北美大陆，中心在其中东部，第三对及以后的模态反映的是次一次的空间特征，分析表明这些NDVI一温度的耦合模态受大尺度的大气环流系统的显著影响，9个重要的大气环流指标能解释整个北半球NDVI方差的55．6％，其中对欧洲、北美东南部，北美西北部，亚洲高纬以及东亚地区的影响最突出，因此，研究未来植被生态系统对全球变化响应的区域特征时，必须要考虑到这些环流系统的可能变化及其影响。     

末次盛冰期以来中国湖泊记录对环流系统及气候类型的响应

为了探讨中国长时间尺度湖泊时空演变规律和潜在的驱动机制,本文在柯本气候分区和中国季风—非季风区的划分基础上,对中国34个有明确数据的典型湖泊运行CCSM 3.0气候模拟系统和水量能量平衡模型模拟其水位变化,同时利用NCEP/NCAR再分析资料对中国按水汽输送划分的季风区进行验证。结果表明,末次盛冰期以来中国湖泊演化主要受千年尺度大气环流的驱动影响,在各个柯本气候区内没有明显的规律性。末次盛冰期以来,在季风区中国湖泊演化主要有早中全新世湖泊水位相对较高以及末次盛冰期和早全新世湖泊水位均较高2种演变规律;在东亚干旱区主要有中晚全新世期间湖泊水位相对较高以及末次盛冰期和中全新世湖泊水位均较高2种演变规律。本文为中国过去气候变化及湖泊演化机制研究提供新的证据,同时为人类全面认识末次盛冰期以来湖泊水位变化提供了新的视角。     

Wavelet analysis of quasi-3-year temperature oscillations in China in last 50 years, and predicted changes in the next 20 years

The wavelet analysis method is used to analyze the annual and winter temperature data of 98 observation stations in China in eight climate zones during the last 50 years （1961-2009）. The periodicities of temperature changes are investigated, and the possible temperature change trends in China in the next 20 years （2012-2029） are also predicted. Our results show that in the inter-annual temperature variability there are pervasive quasi-3- to quasi-4-year cycles, and these cycle changes are relatively steady. The periodic characteristics of the annual temperature changes are clearly different between northern and southern China, and our period superimposition extrapolation shows that both annual and winter temperatures in China will continue to increase in the next 20 years, more so in northern China and in the Qinghai-Xizang Plateau （QXP） than in the southern region, except in the southwest. If temperatures follow historic increasing linear trends, the overall temper- ature is expected to increase by 1℃ between 2010 and 2029.     

萨拉乌苏河流域MGS4层段记录的末次冰期早冰阶气候波动

萨拉乌苏河流域米浪沟湾末次冰期早冰阶时期记录了5.5个由古沙丘砂与河流相、湖沼相构成的沉积旋回。对各沉积旋回的粒度及微量元素分析表明,河流相和湖沼相的平均粒径Mz、分选系数σ和SC/D的值明显高于古沙丘砂,河湖相中的微量元素Mn、P、Rb、Zr、V、Ni含量普遍较古沙丘砂含量高,而Ba、Co等则呈现相反的变化;这些气候代用指标的波动构成了与沉积旋回相对应的5.5个粒度及微量元素变化旋回,指示了该地末次冰期早冰阶至少经历了6次冷干和5次暖湿的气候波动,其中若干次气候回暖事件和冷干事件可与格陵兰冰芯和葫芦洞石笋等记录的D/O事件和Heinrich事件相对应。米浪沟湾剖面地层记录的千年尺度气候波动既是对东亚季风环流演变历史的体现,同时也是对全球气候变化的响应。     

萨拉乌苏河流域微量元素揭示的气候变化

根据毛乌素沙漠东南缘萨拉乌苏河流域滴哨沟湾剖面中更新世晚期以来风成砂与河湖相互为叠覆的沉积记录,利用SPSS软件对P、V、Cr等16种微量元素及Rb/Sr和Sr/Ba比值进行了聚类和相关分析。结果表明：除Sr、Ba、Rb/Sr和Sr/Ba之外的P、V、Cr等14中微量元素反映的气候变化规律较好,其含量的峰值段对应河湖相沉积,而谷值段对应风成砂沉积。根据微量元素含量变化特征及其与地层的对应关系,将萨拉乌苏河流域中更新世晚期以来的气候变化划分为5个阶段：223～196 ka BP,气候温暖湿润,相当于黄土高原S2古土壤发育期;196～148 ka BP,气候干冷,相当于黄土高原L2黄土发育期,属倒数第二次冰期;148～75 ka BP,气候温暖湿润,对应末次间冰期;75～10 ka BP,气候干冷,对应末次冰期;10 ka BP以来,气候以温湿为主。各个阶段还有气候冷暖干湿波动变化。通过与深海氧同位素阶段,冰芯记录变化对比,发现本区气候变化与全球变化具有较好的一致性。