末次冰期毛乌素沙地湖泊消涨过程:沉积证据

毛乌素沙地位于东亚季风边缘区,对于气候变化响应敏感。基于沙地的侵蚀-堆积关系,在侵蚀作用为主的沙地西北部和中部很难找到沉积相对连续且分辨率较高的地层剖面,因此已有的末次冰期古气候环境研究多集中于堆积作用为主的沙地东南缘的萨拉乌苏河河谷地区。本文选取位于沙地腹地,厚度为3.5 m的风成砂-河湖相沉积序列——神水台（SSTG）剖面为研究对象,基于AMS¹⁴C和OSL年代数据,推测得出剖面中湖相层的上界和下界分别为约24.2 ka B.P.和42.7 ka B.P.,依据沉积地层和环境代用指标分析结果,针对末次冰期毛乌素沙地湖泊消涨的一般过程进行了探讨。结果表明,自约5万年以来,由神水台（SSTG）剖面指示了两次明显的湖泊主要发育期,时间分别约为42.7~34.3 ka B.P.和31.1~24.2 ka B.P.,期间粘土含量、有机质、红度均表现为低值,为含淡水螺壳化石的典型湖泊相沉积,且与毛乌素沙地已有湖泊发育的年代结果基本一致。在两期湖相层之间的砂层,平均粒径、砂含量表现为峰值,指示了一次明显的湖泊消退的过程,其时间约为34.3~31.1 ka B.P.;在湖相层上下可能均为风力作用为主导的风沙沉积。通过区域对比并初步探讨其可能的驱动机制,结果表明SSTG剖面记录的湖泊消涨过程主要受控于东亚季风强度的变化。

     

东亚中高纬Heinrich 1事件的表现特征:呼伦湖孢粉记录

Heinrich 1事件是发生于末次冰消期的极端气候突变事件之一,对全球大气环流和陆地生态格局产生了深刻影响。基于对东亚夏季风边缘区最北端呼伦湖HL08孔5.75 m以上沉积岩芯的AMS ¹⁴C定年技术和415~275 cm段140个样品的孢粉分析,重建了东亚中高纬地区呼伦湖21500~13000 cal.a B.P.高分辨率植被变化历史,在此基础上揭示了Heinrich 1事件期间呼伦湖区植被响应过程,明确了Heinrich 1事件在东亚中高纬地区的表现特征。结果显示：呼伦湖区Heinrich 1事件发生于16500~15400 cal.a B.P.,以剧烈降温和显著干旱化为表现特征;事件发生期间湖区周围山地发育亚高山草甸,森林植被稀疏;湖盆区域以藜科为主的荒漠草原显著扩张,区域植被盖度降低、生态环境明显恶化;同时,不同植被类型对Heinrich 1事件的响应存在明显差别,亚高山草甸和蒿属为主的典型草原较藜科为主的荒漠草原和桦属为主的落叶阔叶林响应更为快速、敏感。

     

末次冰消期滇西地区气候突变事件:湖泊孢粉记录

在末次冰消期总体持续增温的过程中,全球气候经历了一系列以"快速增温/降温"为主要特征的千-数十年尺度的突变事件。由于这些气候突变事件具有明显的高频特性,需要在全球范围不同地区开展更多高分辨率的古气候研究,用于进行突变事件的对比和机制的探讨。本研究对比滇西南腾冲青海湖、滇西北泸沽湖和高山湖泊天才湖约2万以来的孢粉、炭屑记录,揭示了中国滇西地区末次冰消期的植被演替与气候变化历史,探讨了末次冰消期存在的气候突变事件。结果表明,滇西地区末次冰消期开始转暖发生在约19 ka（1 ka=1000 cal.a B.P.）;冰消期开始以后,滇西地区气候普遍依次在17.5±0.5~15.2±0.1 ka期间、15.2±0.1~14.3±0.1 ka期间、14.3±0.1~12.9±0.1 ka期间和12.9±0.1~11.7±0.2 ka期间存在冷干-逐渐变暖变湿-明显更暖湿-温度湿度略有下降等这几个突变事件,它们在时间上分别对应于H1冷事件、波令前增暖期、B/A暖期和YD冷事件;滇西地区比较一致地在11.7±0.2 ka进入全新世。除此之外,滇西北地区在约17.7~17.0 ka期间可能还存在一次短暂的较明显的暖湿期。对末次冰消期气候变化机制的探讨认为,末次冰消期开始转暖及以后逐渐增温的趋势主要受夏季太阳辐射量从约20 ka逐渐增加,到11 ka左右达到峰值的控制;而末次冰消期发生的气候突变事件如H1冷事件、波令前增暖期、B/A暖期和YD冷事件主要是受大西洋温盐环流的影响,同时温室气体浓度的变化也起了重要的调制作用。     

Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic ³He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions.Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.     

Climate variability in central China over the last 1270 years revealed by high-resolution stalagmite records

Oxygen and carbon isotopic variations in the upper section of a stalagmite (SF-1) from Buddha Cave (33°40′N 109°05′E) dated by ²³⁰Th/²³⁴U ²¹⁰Pb and lamination counting to a time resolution as fine as 1–3 years have recorded climate changes in central China for the last 1270 years. The changes include those corresponding to the Medieval Warm Period Little Ice Age and 20th-century warming lending support to the global extent of these events. The isotopic records also show cycles of 33, 22, 11, 9.6, and 7.2 years. The 33-year cycle could well represent the ∼35-year periodicity of climate fluctuations previously recognized in China and Europe. Cycles of 22, 11, and 9.6 years have often been associated with the Sunspot or lunar-orbit variations. The 7.2-year cycle was recently identified also in tree-ring records from an area close to Buddha Cave. These cycles suggest that external forcing (e.g. solar irradiance) may affect the summer monsoon over eastern China. The general consistency between the climate characteristics inferred from the stable isotope records of SF-1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate.     

Cryptotephrochronology of the Eemian and the last interglacial–glacial transition in the North East Atlantic

The Eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial. Pronounced climatic oscillations occurred during this period, but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives. Tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons. We outline the identification of three previously unknown cryptotephra horizons within a marine core from the Rockall Trough, North East Atlantic. This sequence preserves a high‐resolution record of this interval and shard size, geochemical heterogeneity and the co‐variance of shard concentrations with ice‐rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway. The main geochemical populations of these horizons have similar transitional alkali major and trace element compositions, suggesting that they were derived from a common Icelandic source, potentially the Öræfajökull volcanic system. These tephra horizons represent additions to the North Atlantic event stratigraphy for this period and tentative correlations to Icelandic terrestrial deposits are proposed for two horizons.     

Last glacial pollen record from Lanzhou (Northwestern China) and possible forcing mechanisms for the MIS 3 climate change in Middle to East Asia

The vegetation on the northeastern margin of the Tibetan Plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive. Pollen samples from the Fanjiaping Loess section in Lanzhou on the western Chinese Loess Plateau (CLP) were analyzed in conjunction with OSL dating. The results indicate that pollen zone B (60.6–46.0 ka, correlative to the early MIS 3) had the greatest abundances of Cupressaceae, Tsuga, Gramineae and Cyperaceae of the entire section, suggesting a warm phase during the last glacial period. These pollen taxa decreased significantly in abundance in the zones C (46.0–39.0 ka) and D (39.0–27.0 ka), reflecting a substantial climate cooling from the middle MIS 3 to MIS 2. These results correlate with climate records from the South China Sea, the CLP, Baikal Lake, North America, North Atlantic Ocean and other regions, and probably correspond with the decline of northern high-latitude insolation and the increase of global ice volume from 50 to 20 ka. In particular, arboreal pollen, fern spore and algae abundances declined sharply since ～40 ka, while shrub and herb pollen reached the highest abundances. Conifer pollen Picea and Abies abundance also rose markedly and increased up the section. This implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since ～40 ka. The decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a ‘snow/ice/albedo’ feedback, which would result in less climate sensitivity to radiative forcing. Meanwhile, vegetation decline in the Northern Hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling, enhancing the growth of polar ice sheets since 40 ka. The development of polar ice sheets increased the polar-to-equator temperature and pressure gradients, strengthening the westerlies and supplying plenty of moisture to Northwest China during 40–30 ka. Lake sediments developed widely on the Tibetan Plateau during 40–30 ka, probably related to an increase in the seasonality of middle-to-low latitude insolation which caused an enhancement of glacier melting on the Plateau.     

Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka

We study the marine and terrestrial contributions in the Gulf of California (GC) to understand the relationship between continental climate and oceanographic variability over the last 28 ka. In Core AII125-8-JPC-20, we examine aeolian and riverine inputs as nutrients for biological productivity. We use biogenic silica (%opal), total organic carbon (%TOC) and calcium carbonate (%CaCO₃) as proxies for primary productivity, and lithic fraction distributions as proxies for terrigenous transport. At the core site, biogenic and lithic components are in phase at millennial-scale in response to regional climate conditions. During the Late Pleistocene, the GC shelf area was above sea level and the western margin showed transient episodes of increased fluvial inputs. Episodic increases in %opal and reduced %TOC suggest upwelling events but ineffective C-export to the sediment. During stadial events (Heinrich 2, Heinrich 1, Younger Dryas), regional declines in %opal, but increases in %CaCO₃ and TOC, suggest efficient C-export by carbonate organisms. During most of the Holocene, dust inputs are higher. Episodic increases in %TOC suggest higher C-accumulation, although this is not controlled by siliceous or calcareous organisms. In the GC, besides upwelling and current advection, nutrient inputs driven by terrestrial climate have an impact on the biological C-pump. © 2020 John Wiley & Sons, Ltd.     

Ice-core pollen record of climatic changes in the central Andes during the last 400 yr

This paper presents a high-resolution ice-core pollen record from the Sajama Ice Cap, Bolivia, that spans the last 400 yr. The pollen record corroborates the oxygen isotopic and ice accumulation records from the Quelccaya Ice Cap and supports the scenario that the Little Ice Age (LIA) consisted of two distinct phases—a wet period from AD 1500 to 1700, and a dry period from AD 1700 to 1880. During the dry period xerophytic shrubs expanded to replace puna grasses on the Altiplano, as suggested by a dramatic drop in the Poaceae/Asteraceae (P/A) pollen ratio. The environment around Sajama was probably similar to the desert-like shrublands of the Southern Bolivian Highlands and western Andean slopes today. The striking similarity between the Sajama and Quelccaya proxy records suggests that climatic changes during the Little Ice Age occurred synchronously across the Altiplano.     

河北安固里淖孢粉记录的晚冰期以来的植被演替与气候变化

河北安固里淖地处东南季风的边缘地区,是研究古气候环境演化的理想地区之一。文章以安固里淖的沉积岩芯（长18.4 m）为研究对象,利用AMS ¹⁴C测年和孢粉数据,重建了安固里淖湖区14.3 cal.ka B.P.以来的植被与气候演化历史。结果表明：14.3~11.0 cal.ka B.P.期间,湖区以疏林草原植被为主,气候偏干;11.0~6.0 cal.ka B.P.以森林草原植被为主,气候湿润;6.0~3.2 cal.ka B.P.以疏林草原植被为主,气候偏湿;3.2~0 cal.ka B.P.以荒漠草原植被为主,气候干旱。总体而言,自晚冰期以来安固里淖的气候经历了由干变湿再逐渐变干的过程,全新世适宜期出现在早中全新世。通过区域对比发现,安固里淖揭示的晚冰期以来东南季风的气候演化特征与西南季风的演化具有很大的相似性,表明晚冰期以来东南季风与西南季风在轨道尺度上的演化并无太大差异,太阳辐射是二者演化的共同驱动力。

     

Evidence for a large surface ablation zone in central East Antarctica during the last Ice Age

Internal isochronous ice sheet layers, recorded by airborne ice-penetrating radar, were measured along an ice flowline across a large (>1 km high) subglacial hill in the foreground of the Transantarctic Mountains. The layers, dated through an existing stratigraphic link with the Vostok ice core, converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base. A two-dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady-state conditions requires net ablation (via sublimation) over the stoss face for the predicted isochrons to match the measured internal layers. Satellite remote sensing data show no sign of exposed ancient ice at this site, however. Given the lack of exposed glacial ice, surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85,000 years to accumulation.     

Variations in the wind‐energy regime of the Taklimakan Desert,central Asia,over the last 700 years as inferred from nebkha sedimentology and chronology

Changes in the wind‐energy environment between AD 1359 and 2010 in the Taklimakan Desert (central Asia) are recorded by the evolution of Chinese tamarisk (Tamarix taklamakanensis) nebkhas. The carbonate component and sedimentological properties of the nebkha excavated during the study, together with AMS ¹⁴C dating control, indicate that significant regional environmental changes have occurred in the central Taklimakan Desert during the last 700 years. The nebkha data presented show that in the periods of AD c. 1480–1560, c. 1640–1690, c. 1760–1820, c. 1860–1930 and c. 1970–1980 the Taklimakan Desert was a relatively high wind‐energy environment. Although changes in the wind‐energy regime in the desert were mainly in phase with fluctuations of the Siberian High, the wind systems and the variations in wind energy exhibit slight differences when compared with the Tarim Basin. Nebkhas that develop in this region originate from the surfaces of mobile dunes or sand sheets, which differs from the origins of nebkhas found in other arid regions of China.     

Pollen records of vegetation and inferred climate change in southwestern Madhya Pradesh during the last ca. 3800 years

Pollen analysis of 1.5m deep sediment core from Sapna Lake, Betul District (M.P.) has demonstrated that between 3,800 and 2,700 yr BP, open Acacia-dominant scrub forests interspersed with stretches of herbaceous vegetation comprising grasses, sedges, Asteraceae, Cheno/Am, etc., occurred in the region under a regime of dry climate. A few trees of Madhuca indica, Holoptelea, Shorea robusta, Lagerstroemia parviflora, etc. were also sparingly distributed therein. The vicinity of the lake was under cereal-based agricultural practice as portrayed by the presence of Cerealia and other culture pollen taxa viz., Cheno/Am, Caryophyllaceae, Artemisia and Cannabis sativa. Around 2,700 to 1,260 yr BP the Acacia-dominant scrub forests were succeeded by the open mixed deciduous forests as evidenced from the improvement in frequencies of Madhuca indica, Sapotaceae, Holoptelea, Shorea robusta as well as sporadic invasion of Terminalia, Mitragyna, Flacourtia, Grewia, Lannea coromandelica, etc. This enhancement in the forest floristic reflects the initiation of a warm and humid climate possibly in response to increasing monsoon precipitation. Owing to the prevailing favourable climatic condition there was acceleration in the agricultural practice as indicated by the rising trend of Cerealia and other culture pollen taxa. Since 1,260 yr BP onwards the depletion in the prominent forest constituents such as Madhuca indica, Sapotaceae, Shorea robusta, Holoptelea and other associated trees implies that the forests turned more sparse and less diversified due to the inception of a warm and less humid climate, attributable to reduced monsoon precipitation. However, the agricultural practice continued with almost same intensity as before, because the Cerealia and other culture pollen taxa remain unchanged.     

Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps)

The glacial history of the Tagliamento morainic amphitheater (southeastern Alpine foreland, Italy) during the last glacial maximum (LGM) has been reconstructed by means of a geological survey and drillings, radiocarbon dating and pollen analysis in the amphitheater and in the sandur. Two phases of glacial culmination, separated by a distinct recession, are responsible for glacial landforms and related sediments in the outer part of the amphitheater. The age of the younger advance fits the chronology of the culmination of the last glaciation in the Alps, well established between 24 and 21 cal ka BP (20 to 17.5 ¹⁴C ka BP), whereas the first pulse between 26.5 and 23 cal ka BP (22 to 21 ¹⁴C ka BP), previously undated, was usually related to older (pre-LGM) glaciations by previous authors. Here, the first pulse is the most extensive LGM culmination, but is often buried by the subsequent pulse. The onset and final recession of the late Würm Alpine glaciation in the Tagliamento amphitheater are synchronous with the established global glacial maximum between 30 and 19 cal ka BP. The two-fold LGM glacial oscillation is interpreted as a millennial-scale modulation within the late Würm glaciation, caused by oscillations in inputs of southerly atmospheric airflows related to Dansgaard-Oeschger cycles. Phases of enhanced southerly circulation promoted increased rainfall and ice accumulation in the southern Alps.     

Cosmogenic radionuclide evidence for the limited extent of last glacial maximum glaciers in the Tanggula Shan of the central Tibetan Plateau

Cosmogenic radionuclide (CRN) exposure ages provide evidence for the limited extent of last glacial maximum glaciers in the Tanggula Shan, central Tibetan Plateau. The most extensive advances occurred during or before marine oxygen isotope stage 6 (MIS-6) based on previous CRN exposure ages. The second most extensive advance occurred during or before MIS-4 based on previous ages and new ages of 41,400 ± 4300, and 66,800 ± 7100 ¹⁰Be yr. A MIS-2 advance of less than 3 km occurred between 31,900 ± 3400 and 16,000 ± 1700 ¹⁰Be yr.     

Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms

The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America at least several times during the Pleistocene. The pattern and timing of its growth and decay are, however, poorly understood. Here, we present a reconstruction of the pattern of ice‐sheet retreat in central British Columbia at the end of the last glaciation based on a palaeoglaciological interpretation of ice‐marginal meltwater channels, eskers and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high‐elevation (1600–2400 m a.s.l.), ice‐marginal meltwater channels is evident across central British Columbia. These landforms indicate the presence of ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east‐central parts of the Interior Plateau during deglaciation. Our reconstruction shows a successive westward retreat of the ice margin from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. The final stage of deglaciation is characterized by the frontal retreat of ice lobes through the valleys of the Skeena and Omineca Mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large‐scale reconfiguration early during deglaciation and was subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.     

湖泊沉积物记录的藏中地区2.8Ma以来的环境演变历史

对青藏高原中部错鄂钻孔岩芯湖泊沉积物δ13C、总有机碳(TOC)、总氮(TN)、C/N和Rb/Sr比值等进行了分析,并结合岩性、孢粉组合特征等,建立了2.8Ma以来藏中地区的环境演化序列、区域构造活动和湖盆演化过程.研究显示,大约在2.8Ma,错鄂构造成盆,2.6Ma的构造运动之后,湖泊扩张,夏季风降水增加,湖泊沉积物以青灰色泥为主,藏中地区总体上处于温湿或凉湿的环境下;约0.78Ma后,沉积岩性明显变粗,湖盆快速充填,反映了强烈的构造隆升运动,并使高原中部整体隆升到4000m以上,δ13C和TOC反映藏中地区环境具明显的高寒特点;高原剧烈隆升时期,化学风化较弱,而在高原相对稳定的剥蚀夷平阶段,化学风化较强,说明藏中地区的化学风化在受气候强烈影响的同时,又受高原阶段性的构造隆升所控制.     

过去千年东亚与全球百年尺度温度同步性变化的模拟研究

利用美国国家大气研究中心（NCAR）提供的过去千年（850~2005年）集合模拟试验（CESM-LME）资料,在与重建资料、现代观测/再分析资料进行对比验证的基础上,分析了过去千年不同世纪东亚与全球地表温度变化的同步性,并结合单因子敏感性试验结果,分析了造成东亚与全球地表温度各个世纪同步性及变化幅度差异的原因。结果表明：过去千年里,在20世纪以前,东亚地区与全球均经历了中世纪暖期与小冰期,温度变化在百年尺度上整体一致,10世纪、11世纪、13世纪、18世纪和19世纪东亚与全球温度变化同步性较高,差异较小;但在12世纪、14~17世纪中,其变化振幅存在显著差异,东亚地区温度变化幅度总体上小于全球,太阳辐射和火山活动等自然外强迫及内部变率对差异的形成可能起到了主导作用;而20世纪以来,两者变化显示出较大的不同步性,东亚地区温度增长没有全球温度增长剧烈,甚至出现了降温,人为外强迫在这一时期起主导作用。温室气体浓度变化对温度的影响在两极有明显的放大效应,是东亚与全球温度变化差异形成的主要原因,同时,人为气溶胶排放使得东亚地区温度降低也是东亚与全球温度变化不同步的原因之一。

     

Source of a freshwater influx at the last glacial maximum in the Indian Ocean: An alternative interpretation

Recent analysis of a sediment core in the eastern Arabian Sea revealed a negative pulse of about 1% in the δ¹⁸O value of the planktonic Foraminifera around the last glacial maximum (LGM). This pulse has been attributed to (i) increased runoff into the Bay of Bengal from the east-flowing south Indian rivers due to enhancement of the northeast winter monsoon, and (ii) an increase in Arabian sea-surface temperature caused by the weakening of the southwest monsoon at the LGM. We show that the speculation on which the latter hypothesis is based, is not supported by observational data and cannot fully account for the observed magnitude of the spike. With a view to assessing the validity of the first mechanism, we have modelled the mixed layer of the Bay of Bengal as a well-mixed box. The model calculations show that to account for the pulse requires a change of about 10% in either the annual rate of river input or its isotopic composition. For the northeast monsoon to account for the pulse it would mean that the rainfall should have increased by a factor of five to ten during the LGM. No evidence for such an increase is indicated in the available palaeoclimatic data. We explain the freshwater spike by invoking increased discharge of glacial meltwater from the Tibetan plateau into the Bay of Bengal. We show that the proxy climate data from the Indo-Tibetan region that has become available recently provides substantial evidence for the occurrence of a warming event around the LGM, which supports our mechanism.     

Holocene environments and climate in the Mongolian Altai reconstructed from the Hoton-Nur pollen and diatom records: a step towards better understanding climate dynamics in Central Asia

This study presents the results of the palynological and diatom analyses of the sediment core recovered in Hoton-Nur Lake (48°37′18″N, 88°20′45″E, 2083 m) in 2004. Quantitative reconstruction of the Holocene vegetation and climate dynamics in the semiarid Mongolian Altai suggests that boreal woodland replaced the primarily open landscape of northwestern Mongolia at about 10 kyr BP (1 kyr = 1000 cal yr) in response to a noticeable increase in precipitation from 200–250 mm/yr to 450–550 mm/yr. A decline of the forest vegetation and a return to a predominance of open vegetation types occurred after 5 kyr BP when precipitation sums decreased to 250–300 mm/yr. Prior to 11.5 kyr BP diatom concentrations are relatively low and the lake is dominated by planktonic Cyclotella and small Fragilariaceae, suggesting the existence of a relatively deep and oligotrophic/mesotrophic lake. The great abundance of Staurosirella pinnata from the beginning of the record until 10.7 kyr BP might imply intensified erosion processes in the catchment and this is fully consistent with the presence of scarce and dry vegetation and the generally arid climate during this period. From about 10.7 kyr BP, more planktonic diatom taxa appeared and increased in abundance, indicating that the lake became more productive as diatom concentration increased. This change correlates well with the development of boreal woodland in the catchment. Decrease in precipitation and changes in the vegetation towards steppe are reflected by the rapid increase in Aulacoseira distans from about 5 kyr BP. The Holocene pollen and diatom records do not indicate soil and vegetation cover disturbances by the anthropogenic activities, implying that the main transformations of the regional vegetation occurred as a result of the natural climate change. Our reconstruction is in agreement with the paleomonsoon records from China, demonstrating an abrupt strengthening of the summer monsoon at 12 kyr BP and an associated increase in precipitation and in lake levels between 11 and 8 kyr BP, followed by the stepwise attenuation of the monsoon circulation and climate aridization towards the modern level. The records from the neighboring areas of Kazakhstan and Russia, situated west and north of Hoton-Nur, demonstrate spatially and temporally different Holocene vegetation and climate histories, indicating that the Altai Mountains as a climate boundary are of pivotal importance for the Holocene environmental and, possibly, habitation history of Central Asia.