青藏高原昆仑山垭口盆地晚上新世以来沉积物磁化率与气候变化

通过对青藏高原昆仑山垭口盆地磁化率、频率磁化率环境重要参考指标的分析,并与黄土—古土壤和深海δ18O记录的气候变化进行对比,结合剖面的岩性特征和年代序列以及前人所获得的粒度和孢粉资料,揭示了3.6Ma～0.5Ma期间昆仑山垭口盆地气候变化经历了6个不同的阶段:3.6Ma～2.48Ma气候相对冷干,2.48Ma～2.14Ma气候偏凉湿,2.14Ma～2.07Ma气候相对冷干,2.07Ma～1.16Ma气候总体相对较湿润(其间有数次冷干波动),1.16Ma～0.78Ma气候偏冷干以及0.78Ma～0.5Ma气候向冷湿发展。     

A lacustrine record from Lop Nur,Xinjiang, China: Implications for paleoclimate change during Late Pleistocene

Climate variability during the Late Pleistocene is studied from the proxies in core CK-2 drilled from the Luobei Depression (91°03′E, 40°47′N), Lop Nur in the eastern Tarim Basin, Xinjiang, China. Geophysical and geochemical properties, including magnetic susceptibility, granularity, chroma, carbonate content, loss on ignition and trace elements, have been determined to reconstruct the environmental evolution of the area during 32–9 ka BP. The chronology is established by uranium–thorium disequilibrium dating techniques.Our data suggest four paleoclimate stages, indicating glacial variations between cold–humid and warm–arid environments. A period of extreme humidity occurred during 31,900–19,200 yr BP is attributed the last glacial maximum (LGM). The period was followed by a warm–arid episode during 19,200–13,500 yr BP. Then a cold–humid interval during 13,500–12,700 yr BP may correspond to another cooling phases at high latitudes of the Northern Hemisphere. The last stage from 12,700 to 9000 yr BP has a trend that the climate turned warm and arid. The Lop Nur region is characterized by particularly humid stadials and arid interstadials. The climate variability in Lop Nur was constrained by global climate change because it is correlated with Dansgaard–Oeschger and Heinrich events, which were observed at the northern high latitudes. The synchroneity of the palaeoclimatic events suggested that cold air activity at the northern high latitudes was the most important factor that influenced the climate evolution in the Lop Nur region. A probable mechanism that involves the migration of westerly winds is proposed to interpret this synchroneity.     

晚更新世晚期以来滇西北高原的孢粉记录与我国南方石笋记录的气候变化对比研究

运用古气候参数方法对滇西北高原YXL剖面进行孢粉分析,结合定年数据,重建了该地区晚更新世晚期以来的植被变化和气候变化并与我国南方石笋记录等进行对比分析。研究表明:从大约31570cal.yrBP以来,滇西北高原总体经历了温凉偏干-冷干-略转暖湿-冷干-转暖增湿-冷干-转为暖湿-温和偏干-温凉偏干的气候变化历程,其间多有反复;YXL剖面孢粉记录与董哥洞、葫芦洞石笋记录在古气候变化大趋势上基本一致,对H2、H1、YD、MWP、LIA等气候事件反映明显;YXL剖面孢粉记录中全新世大暖期升温增湿的速度慢于石笋记录和冰芯记录,其干冷气候期持续时间较长,这些特点均与高原环境有关,并受到青藏高原的影响,具有一定的区域性意义。      

Hydrological and climatic changes in deserts of China since the late Pleistocene

Large areas in western China were wetlands or less arid between 40 and 30 ka, corresponding to the “Greatest Lake Period” on the adjacent Tibetan Plateau. During the last glacial maximum, some of these western Chinese deserts again experienced wetter conditions; however, at the same time the sandy lands in the eastern Chinese desert belt experienced an activation of aeolian dunes. While interpretations of the mid-Holocene environment in the deserts of China are controversial, it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies. Evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems, as well as other paleoenvironmental proxies such as the Artemisia/Chenopodiaceae ratio, should be interpreted with greater caution. Facing the highlighted uncertainties in our understanding of climate changes in Chinese deserts, it is hoped that this special issue will improve our knowledge considerably.     

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.     

A late Pleistocene long pollen record from Lake Urmia, NW Iran

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.     

Oxygen-isotope record of Late-Glacial climatic change in western Ireland

Oxygen-isotope profiles for the Late-Glacial carbonate sediments from Red Bog and adjacent Lough Gur in County Limerick in western Ireland are readily correlated with the classical hiozones delineated on pollen diagrams for the same cores. The estimated summer temperatures of the Bølling/Allerød were as high as those in the early Holocene and are correlated with increasing Milankovitch summer insolation. This warm phase was abruptly terminated in the Younger Dryas cold episode by a depletion of 4% in δ¹⁸O, suggesting a summer atmospheric temperature decrease of about 12°C, comparable to that inferred from fossil beetle data. The Younger Dryas phase is attributed to a major cooling of the sea-surface temperature by a postulated discharge of icebergs similar to that of the Heinrich events, for the icebergs were much more effective than simple meltwater in cooling the sea surface and thus the climate over Europe. Shorter-term cool phases (Older Dryas. Gerzensee. Preboreal oscillation) are also recognized.     

A Lateglacial and Holocene organic carbon isotope record of lacustrine palaeoproductivity and climatic change derived from varved lake sediments of Lake Holzmaar,Germany

A composite varve-dated 11.4 m long sediment sequence from Lake Holzmaar, situated in the Eifel region of western Germany, was investigated for total organic matter content, total nitrogen content and stable organic carbon isotopes. Mean time resolution is 75 years for TN and 14 years for δ¹³C_org. On millennial time scales primary production of lacustrine algae strongly depends on the delivery of nutrients from the catchment. The respective carbon isotope record is characterized by marked variations of δ¹³C_org ranging from −36.0‰ to −27.0‰ and includes a number of pronounced shifts. Reactions of the lacustrine system and the catchment to changes of environmental parameters, e.g. runoff, solar radiation and temperature, induce changes of algal associations and of lacustrine primary production which are reflected in the sediments as carbon isotope variations. Clear evidence of ecosystem reorganizations is detected by the carbon isotope record around 14,200, 10,400, 9600, 5500, 2700, 1700 and 900 varve years BP. In particular, the Holocene events of 9600, around 5500 and 2700 are interpreted as the expression of massive changes of the climate system. The steady rise of δ¹³C_org values during the mid-Holocene is interpreted as a continuous climatic amelioration reaching an optimum around 6500 varve years BP. Rapid and large changes of δ¹³C_org values from 2700 varve years BP to the present indicate major disturbances in the catchment area. These are most probably related to deforestation or reforestation and runoff changes, presumably in conjunction with human impact. Carbon isotopes, thus, characterize the Holzmaar ecosystem in time revealing lacustrine palaeoproductivity as well as providing palaeoenvironmental and palaeoclimatic information.     

A late Early Pleistocene pollen record from Fontana Ranuccio (central Italy)

A pollen record from a sediment core drilled underneath the Acheulian site of Fontana Ranuccio provides new data on the vegetation characters in central Italy during the late Early Pleistocene, in a forest phase possibly corresponding to a substage of Marine Isotope Stage 21. A number of tree taxa nowadays extinct in Europe (Cathaya, Tsuga, Taxodium type, Carya and Pterocarya) are present at Fontana Ranuccio in a temperate phase characterised by dense forest conditions, dominated by Alnus and Pterocarya. The comparison of the Fontana Ranuccio record with other dated sites distributed along the Italian peninsula indicates that the floristic and vegetational characters of the Mid Pleistocene revolution present a rather distinct succession of biostratigraphic events. Compared to other Early Pleistocene pollen records from southern Europe, the Italian Peninsula shows greater floristic similarities with the Eastern Mediterranean regions than with the Iberian Peninsula. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiarchive paleoseismic record of late Pleistocene and Holocene strong earthquakes in Switzerland

A multiarchive approach has been applied to the investigation of the late Pleistocene and Holocene record of strong earthquakes in Switzerland. The geological archives used for this study include active faults, lake deposits, slope instabilities, and caves. In the Basle area, eight trenches were opened across the Basle–Reinach fault, nearby rockfall deposits were systematically investigated, sediment cores were taken from two lakes, and nine caves were studied. In Central Switzerland, five lakes were investigated by means of high-resolution seismic lines and sediment cores. Furthermore, three caves were studied in Central Switzerland. Altogether, the investigations are based on more than 350 km of high-resolution reflection seismic lines, 450 m of core samples, 260 m of trenches, and 245 radiocarbon age determinations. The measured co-seismic displacements along the Basle–Reinach fault supply independent information for the magnitude of the AD 1356 Basle earthquake exclusively based on geological evidence. Deformation features related to three well-documented strong historic earthquake shocks were identified. Deformation features of the AD 1774 Altdorf and AD 1601 Unterwalden earthquakes can be used to calibrate paleoseismic evidence in Central Switzerland. Altogether, traces of 13 earthquakes could be found in the two study areas, all of them with magnitudes M_w  6 or greater. For the first time, the earthquake catalogue for Switzerland can be extended back beyond historic records, into the late Pleistocene, spanning 15,000 years.     

西藏纳木错和藏北高原古大湖晚更新世以来的湖泊演化与气候变迁

根据野外水准测量与室内实验分析，本文探讨了西藏纳木错和藏北高原古大湖晚更新世以来的湖泊演化和气候变迁。在纳木错沿岸拔湖48m以下，发育了6级湖岸阶地，拔湖48-139．2m发育有高位湖相沉积。研究表明，纳木错湖泊发育与藏北高原东南部古大湖演化可划分为3个阶段：①116-37ka B．P．间的古大湖期；②37-30ka B．P．间的外流湖期；③30kaB．P．以来的纳木错期。在古大湖阶段，包括纳木错、色林错和扎日南木错、当惹雍错等藏北高原东南部的一大批现代大、中、小型湖泊，都是互相连通的一个古大湖，其范围可能超过了现代的藏北内、外流(怒江)水系的分水岭。它或许还与藏北高原南部和西部的其他古湖相连，成为统一的藏北高原“古大湖”。通过对纳木错湖相沉积形成时代与深海氧同位素对比，易溶盐、pH值、地球化学、介形类和孢粉分析等的综合研究发现，湖相沉积记录了自晚更新世以来的湖泊演化和气候变迁信息。资料显示古大湖期湖面最高，气候温和清爽；外流湖期湖面急剧下降，气温和湿度较现今略高；纳木错期以来气候经历了全新世最宜期的暖湿后日益干旱化，气温波动，湖面持续下降。表明自晚更新世以来该区气候在逐渐变干的总趋势的基础上，经历了多次明显的冷暖与干湿波动。     

A multi-proxy lacustrine record of Holocene climate change on northeastern Baffin Island, Arctic Canada

Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomid-inferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5°C warmer than historic summer temperatures from 10,000 to 8500 cal yr B.P. Following rapid cooling 8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern Canada. However, the lacustrine proxies in Lake CF3 apparently responded to insolation-driven warmth, despite the proximity of Lake CF3 to the Laurentide Ice Sheet and its meltwater. The magnitude and timing of the Holocene thermal maximum at Lake CF3 indicate that temperatures and environmental conditions at this site are highly sensitive to changes in radiative forcing.     

A Holocene lacustrine record of environmental change in northeastern Prince of Wales Island, Nunavut, Canada

A core from Prince of Wales Island in the central Canadian Arctic was analysed for pollen and sediment characteristics. From 9200 yr BP to 7000 yr BP, the landscape supported a pioneer vegetation under cold conditions, with relatively high sediment input to the lake. Between 7000 and 4000 yr BP there was a period of high pollen concentrations, more abundant Cyperaceae and Dryas on the landscape and finer sediment input. In the last 4000 years, climate cooling is indicated.     

Revisiting the late Pleistocene mammal extinction record at Tight Entrance Cave, southwestern Australia

Tight Entrance Cave (TEC) in southwestern Australia provides a Pleistocene sequence documenting the extinction of 14 large mammal species. This record has been interpreted as indicating that extinctions did not occur during or before the penultimate glacial maximum (PGM) and that humans played a primary role in the extinctions. However, it remains possible that the majority of extinct megafauna persisted no later than the PGM. The TEC extinctions correspond with vegetation change, a cooling/drying trend, increased biomass burning, and increasingly unstable small mammal communities. The initiation of these trends predates human arrival on the continent and implies environmentally mediated extinctions.     

Megafauna demography and late Quaternary climatic change in Australia: A predisposition to extinction

Arguments about the extinction of Australia's megafauna have largely rested on anthropogenic factors consequent upon the arrival of humans there, and have lacked any appreciation of the possibilities of climate/environmental changes taking place during the late Quaternary. Moreover, the status of the megafauna at the extinction and in the period leading up to it has largely been ignored. This article assesses the species that existed during the late Quaternary, their continental dispersal, the likely impact of negative climate change during that time and the effect this had on their demography and variety. These factors are discussed together with a synthesis of present data regarding Australia's mega 2004: fauna demography and which species may have reached the extinction threshold. One interpretation of the data suggests a mid–late Quaternary process of demographic fragmentation, disjunction and fluctuation, a restricted continental distribution among a diminishing group and a limited and reducing species variety due to climate and environmental change. It is argued that increasing continental aridity during the mid–late Quaternary was a forcing mechanism behind species distribution, changes to that distribution and population reduction through episodic but widespread drought and vegetation change. This resulted in alteration of the biogeographic status of the megafauna, with increasing stress on and reduction of the population as a whole. In particular, it changed population composition and reduced species variety and overall population size by the beginning of the last glaciation, such that at the time of human entry the population had reached a precarious stage vulnerable to any level of subsequent anthropogenic activity with the arrival of humans in Australia.     

Late Pleistocene equilibrium-line reconstructions in the northern Peruvian Andes

Equilibrium-line-altitude (ELA) reconstructions using the toe-to-headwall-altitude ratio method for paleoglaciers in the Cordilleras Blanca and Oriental, northern Peruvian Andes (7–10°S; 77°20'–77°35'W), indicate that ELAs during the last glacial maximum (LGM; marine isotope stage 2) were c . 4300 m in the Cordillera Blanca, c . 3900–3600 m on the west side of the Cordillera Oriental, and c . 3200 m on the east (Amazon Basin) side of the Cordillera Oriental. Comparison with estimated modern ELAs and glaciation thresholds indicate that ELA depression ranged from c . 700 m in the Cordillera Blanca to c . 1200 m on the east side of the Cordillera Oriental. This augments data from many mountain ranges in middle- and low-latitude regions that indicate that ELAs during the LGM were depressed by c . 1000 m. Published palynological evidence for drier conditions during the LGM in the tropical Andes suggests that ELA depression of this amount involved a temperature reduction (> 5–6°C) that greatly exceeded the tropical sea-surface temperature depression estimates of CLIMAP (< 2°C). The west to east increase in ELA depression during the LGM indicates that the steep modern precipitation gradients may have been even steeper during the LGM.     

The last occurrence of Pleistocene megafauna in the Ecuadorian Andes

The latest Pleistocene—Holocene megafauna extinction is a global event, particularly dramatic in the Americas. In a previous paper the authors hypothesised a scenario for this extinction event in South America, where mastodonts first suffered from the changing climate environment, followed by the mylodonts and equids. These different latest Pleistocene—Holocene megafauna extinction “waves” in Ecuadorian Andes have been dated using ¹⁴C methods on material from selected sites in north and central Ecuadorian Interandean Depression. An outline of the physiographic evolution of the Interandean Depression in Ecuador is offered and the stratigraphic setting of the fossiliferous sites is discussed. The present results confirm the author's hypothesis on the megafauna extinction pattern, previously published in terms of relative age. The importance of climatic changes during Last Glacial Maximum at low latitudes is discussed.     

A late Pleistocene record of aeolian sedimentation in Blanche Cave, Naracoorte, South Australia

We provide geochemical analyses and grain size data for a clearly layered, 80 cm thick sedimentary deposit close to a roof collapse in Blanche Cave near Naracoorte in SE South Australia. This deposit contains aeolian material deposited between 40 ka and 14 ka cal BP and which yields airborne sediments spanning the Last Glacial Maximum, a period of time with little information for the Australian continent. The deposit also contains abundant vertebrate fossil material derived from owl pellets, accumulation and pitfall entrapment. Below the studied profile, large vertebrate remains are found but are not discussed here. No Holocene sedimentation occurred at the site examined in the cave, and the top of the sequence is capped with a layer that has been anthropologically disturbed and contains exotic Pinus pollen. Chronologies of the deposit were obtained using two dating techniques: single stage accelerator mass spectrometer (SSAMS) ¹⁴C analysis of 23 charcoal samples and optically stimulated luminescence (OSL) dating of quartz from 6 sediment samples. The ¹⁴C chronology is preferred to describe the history of the deposits since the OSL chronology, which consistently overestimates the associated radiocarbon dates, may be inaccurate due to complexities in calculating dose rates, and may in addition represent the timing of sediment deposition through the cave opening rather than sediment transport to the deposit site. Morphological analysis of single quartz grains and grain size analysis indicate different provenance that is confirmed through the geochemical analyses of bulk sediment. Major elements were measured by X-ray Fluorescence (XRF), trace and rare earth elements by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICP-MS), and Neodymium isotopic ratios were obtained using a Thermal Ionisation Mass Spectrometer (TIMS).Our results indicate that the aeolian material deposited in Blanche Cave over the 40–14 ka cal BP period originated from different sources across South Australia, although Nd isotopes clearly indicate a close association with sediments of the Kanmantoo Group outcropping along the eastern portion of the Mount Lofty Ranges and the Padthaway Ridge further south, both being located to the NW and NNW of the cave. During the latter part of Marine Isotope Stage 3, conditions were wetter and windblown sediment came from the coastal region just north and south of the Coorong Lagoon, with winds originating from the north-northwest. At that time, woody taxa appear to have vegetated the landscape. During the drier phases, especially the Last Glacial Maximum, sediment came from further inland, thus suggesting a different predominant wind direction, more from the northwest. The deglaciation saw material originating from a more northerly direction.