南岭东部新仙女木事件的孢粉学证据

冰消期至早全新世的新仙女木事件（ＹｏｕｎｇｅｒＤｒｙａｓ,简称ＹＤ）,因降温时间短,气候波动强,是全球气候变化研究者关注的热点。根据近期的研究［１～３］,ＹＤ事件在欧洲、北美和我国北方都有所表现。但在我国长江以南的内陆地区,未见报道。笔者在用孢粉资料...     

Plant survival in Iceland during periods of glaciation?

Aim The paper addresses the classical question of possible plant survival in Iceland during the last glacial period in the light of a palaeobotanical record from northern Iceland, spanning the period 11,300–9000 BP , including the Younger Dryas stadial. We review the Late Cenozoic fossil plant record, the past debate on glacial plant refugia in Iceland, and the evidence for ice-free areas during the Weichselian. Location The investigated lake sediment record comes from Lake Torfadalsvatn, which is situated in the northwestern part of the Skagi peninsula in northern Iceland. Methods The sediment chronology was constructed from the cccurrence of the Vedde Ash and the Saksunarvatn ash, two well-dated Icelandic tephras, together with the results from five AMS and conventional radiocarbon dates performed on bulk sediment samples. The vegetational reconstruction was based on detailed pollen analysis of the sediment sequence. Results The pollen analysis revealed that many of the taxa present in the area prior to the Younger Dryas stadial continued to produce pollen during that cold event. The more or less immediate reappearance of a few other pollen taxa at the Younger Dryas-Preboreal boundary suggests that these plants also survived, even if they did not produce sufficient pollen to be recorded during the Younger Dryas stadial. Main conclusions We conclude that the relatively high plant diversity found in high Arctic areas and present-day nunataks in Iceland and Greenland, together with the fact that many plant species were able to survive the Younger Dryas stadial on the Skagi peninsula, suggest that species with high tolerance for climate fluctuations also survived the whole Weichselian in Iceland. This conclusion is supported by recent palaeoclimatic data from ice-cores and deep-sea sediments, indicating that Icelandic climate during the last glacial was only occasionally slightly colder than during the Younger Dryas stadial.     

Late-glacial vegetational ecotones and climatic patterns in Western Norway

The mapping of Weichselian late-glacial interstadial (13-11 ka B.P.) and Younger Dryas stadial (11-10 ka B.P.) pollen percentages for selected taxa demonstrates vegetational and hence climatic differentiation in Western Norway during these times. In the south, early interstadial Salix dominance was replaced by Betula woodland development. During Younger Dryas time, Betula pollen declined to values consistent with a modern vegetational analogue of the vegetation at the upper forest limit. In the inner fjord areas north of Stavanger, the interstadial vegetation contained scattered birch trees, the density depending on local topography and soils. During the Younger Dryas, vegetation resembling the modern mid- and low-alpine vegetation developed. On the outer coast, the interstadial vegetation was probably treeless, and dominated by Salix spp., including S. herbacea, and herbs. The vegetation became even more open during the Younger Dryas, resembling that of the modern mid- and high-alpine zones. The spatial ecotones delimiting the three areas of different vegetation development during both the interstadial and the Younger Dryas can be placed north of Stavanger, separating the southern region, and between the outer coast and inner fjord areas to the north. The Younger Dryas drop in temperature in all areas was up to about 5°C, enough to pass ecotonal thresholds in time in all areas.     

The Allerød/Younger Dryas transition in Wolin Island, northwest Poland, as reflected by pollen, macrofossils, and chemical content of an organic layer separating two aeolian series

A palaeoecological study including pollen, macrofossils, and chemical analyses of an organic sediment separating two series of aeolian cover sands has enabled us to reconstruct environmental changes during the Allerød/Younger Dryas transition in Wolin Island, northwest Poland. The Allerød woodland dominated by Pinus sylvestris became more open at the beginning of the Younger Dryas, when aeolian (wind) activity resulted in instability of the soil. During the early phase of the Younger Dryas the water level in the local basin distinctly raised, indicating a change to a wetter climate. This short-lasting phase was followed by an increased frequency and intensity of aeolian processes. However, the main aeolian event took place before the major expansion of Juniperus, not later than 10,780±120 b.p. Frequent woodland fires, probably due to the activities of Palaeolithic people, have been documented both for the Allerød and the Younger Dryas periods. Macrofossils of Alnus sp. found in the Allerød layer are of special interest in showing the presence of alder trees in northwest Poland as early as the Late-glacial.     

Lake–peat bog transformation recorded in the sediments of the Stare Biele mire (Northeastern Poland)

The history of Stare Biele paleolake (northeast Poland) has been reconstructed using subfossil Cladocera remains and pollen and spores of aquatic and mire plants from a sediment core. Sediment accumulation began approximately 12,000 years ago during the Older Dryas chronozone. Throughout the entire Late Glacial period, the basin was a small, low-trophic state lake with a developed open-water zone. A well-recorded increase in the trophic state started at the beginning of Holocene. The lake reached its highest trophic level during the early and middle Atlantic chronozone. The first human activity in the lake catchment area occurred at this time, as recorded by fern spores and numerous charcoal grains. Repeated rises in lake water level are documented at the beginning and throughout the early part of the Younger Dryas. Two clear events of decreasing lake water levels are recorded, first during the middle part of the Younger Dryas and second in the Preboreal. Terrestrialization processes first intensified at the end of Atlantic period, which appears to correspond to a decrease in pH. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Reconstruction of Late Pleistocene-Holocene palaeobathymetries from Ostracoda on the Tyrrhenian continental shelf

Quantitative analyses of ostracod assemblages from three cores recovered on the Tyrrhenian shelf (Gaeta and Salerno Gulfs) have been applied to construct palaeobathymetric curves. Palaeoclimatic curves obtained from planktonic foraminifera, calcareous nanoplankton, pteropods and pollen are available for the same cores, in addition to sedimentological, mineralogical, geochemical (δ¹⁸O, ¹⁴C, C/N, CaCO₃) and volcanological data with regard to the two cores from the Salerno Gulf. The palaeobathymetric curves reflect the climatic events through the Late Pleistocene-Holocene interval. The climatic events of the Last Glacial (and within it, the Last Glacial Maximum), the Late Glacial (with Oldest Dryas, Bølling-Allerød, Younger Dryas events) and Postglacial have been recognised. The palaeobathymetric curves are also in agreement with palaeoclimatic curves of planktonic assemblages and pollen.     

Continental-scale tree population response to rapid climate change, competition and disturbance

Aim  Using a new approach to analyse fossil pollen data, we investigate temporal and spatial patterns in Populus ( poplar, cottonwood, aspen) from the Late Glacial to the present at regional to continental scales.
Location  North America.
Methods  We extracted data on the timing and magnitude of the maximum value of Populus pollen from each pollen diagram in the North American Pollen Database (NAPD). The information was plotted in histograms of 150-year bins to identify times when Populus was abundant on the landscape. We also mapped the maximum values to identify spatial patterns and their causes.
Results  Our analyses show that there have been several periods since the Late Glacial when Populus was abundant on the landscape: (1) from 12.35 to 12.65 kyr  bp , in eastern North America, largely in response to the opening of the forest following the onset of the Younger Dryas; (2) from 10.85 to 11.75 kyr  bp , following the termination of the Younger Dryas; and (3) during the last 150 years, as land was cleared for agricultural use, especially in the midwestern United States.
Main conclusion  Since the Late Glacial, changes in the abundance of Populus were caused more by the effects of abrupt climate change on its major competitors, rather than the direct effects of climate on Populus itself.     

An 11400 year paleoecological history of a British chalk grassland

The first broad-based, paleoecological analysis of a sedimentary sequence on the British chalk, dating to the terminal Pleistocene, reveals a history of climatic, vegetational and faunal change. The past co-occurrence of currently allopatric species among molluscs, beetles and plants supports hypotheses of the impermanence of communities. Modern pollen rain data are utilized to refine the ecological interpretation of the fossil pollen data. The presence of the Windermere Interstadial (Allerod) and the Loch Lomond re-advance (Younger Dryas) are represented by decreased abundances of arboreal taxa and increased representation of cold grassland elements. Open grassland habitats appear to have been a continuous landscape element, at least locally, since the late-glacial period on the northern British chal Mands, although their species composition has changed greatly in the last 11400 yr.     

A 12 000-year record of environmental change in the Lomond Hills, Fife, Scotland: Vegetational and climatic variability

The Lomond Hills of Fife, an isolated upland area rising to over 500 m, provide an opportunity to investigate the effect of altitude on vegetation and climate in an area otherwise dominated by lower-lying land. The West Lomond site contains sediments of the Devensian Late-glacial period; they reveal a well-defined sequence of Bolling-Older Dryas-Allerod-Younger Dryas events, commencing ca. 12 190 radiocarbon years B.P. and a probable Amphi-Atlantic Oscillation between ca. 11 040 and 10 800 B.P. The Holocene record is constrained by low sediment input but does reveal a woodland presence at this altitude, dominated byBetula andCorylus. Size statistics forBetula pollen are presented and the implications of the vegetational and climatic record are discussed. The traditional view of a smooth progress towards more temperate conditions following the Younger Dryas is not supported; between 10 180 and 9120 B.P., three cooler periods are inferred, the earliest of which may belong to a terminal phase of the Younger Dryas. Comparative pollen ‘influx’ data strongly suggest thatQuercus,Ulmus andAlnus were not present locally. As a working hypothesis, it is suggested that the demise of woodland, from ca. 5950 B.P., was a result of exposure. Pollen indicative of human impact was probably derived from areas of lowland agricultural activity from ca. 5330 B.P. onwards.     

Vegetation and Climate Change during the Last Deglaciation in the Great Khingan Mountain,Northeastern China

The Great Khingan Mountain range, Northeast China, is located on the northern limit of modern East Asian Summer Monsoon (EASM) and thus highly sensitive to the extension of the EASM from glacial to interglacial modes. Here, we present a high-resolution pollen record covering the last glacial maximum and the early Holocene from a closed crater Lake Moon to reconstruct vegetation history during the glacial-interglacial transition and thus register the evolution of the EASM during the last deglaciation. The vegetation history has gone through distinct changes from subalpine meadow in the last glacial maximum to dry steppe dominated by Artemisia from 20.3 to 17.4 ka BP, subalpine meadow dominated by Cyperaceae and Artemisia between 17.4 and 14.4 ka BP, and forest steppe dominated by Betula and Artemisia after 14.4 ka BP. The pollen-based temperature index demonstrates a gradual warming trend started at around 20.3 ka BP with interruptions of several brief events. Two cold conditions occurred around at 17.2–16.6 ka BP and 12.8–11.8 ka BP, temporally correlating to the Henrich 1 and the Younger Dryas events respectively, 1and abrupt warming events occurred around at 14.4 ka BP and 11.8 ka BP, probably relevant to the beginning of the Bølling-Allerød stages and the Holocene. The pollen-based moisture proxy shows distinct drought condition during the last glacial maximum (20.3–18.0 ka BP) and the Younger Dryas. The climate history based on pollen record of Lake Moon suggests that the regional temperature variability was coherent with the classical climate in the North Atlantic, implying the dominance of the high latitude processes on the EASM evolution from the Last Glacial Maximum (LGM) to early Holocene. The local humidity variability was influenced by the EASM limitedly before the Bølling-Allerød warming, which is mainly controlled by the summer rainfall due to the EASM front covering the Northeast China after that.     

Reconstruction of late-glacial and holocene environments in southeast France based on the study of a 66-m long core from Biot, Alpes Maritimes

A pollen analytical study of a 66-m long core from the Brague valley, Biot, Alpes-Maritimes, France, suggests that thalwegs in eastern Provence may have served as refugia for mesophilous trees such asTilia, Fagus andAbies during the last glacial period. During the Younger Dryas the vegetation was considerably less steppic in character than that described from western Provence. The varying role of taxa such asQuercus ilex-type in pollen profiles from the wider region suggests a longitudinal gradient in both climate and vegetation development in the French/Italian north-western meditcrranean region during the Holocene.     

Palynological evidence for plant-animal interaction in the late Holocene

Pollen grains of Centaurea cyanus and Polygonum aviculare are common indicators of the activity of man in palaeoenvironmental reconstructions. Studied through pollen analysis, the vegetation history of Holocene deposits reveals numerous occurrences of atypical grains of these species in the youngest pollen zones. Other pollen types with the same atypical features as the taxa mentioned above also occur sporadically; these include Centaurea rhenana/jacea and Apiaceae. The occurrence of some of these pollen types is not only restricted to the period of human impact. They are also noted in earlier periods—in the Younger Dryas, in the Eemian interglacial and in the Saalian. It is possible that a large proportion of the pollen introduced into lake deposits had passed through the throats and abdomens of various animals. The pros and cons of possible explanations are considered in this paper.     

Anti-phase oscillation of Asian monsoons during the Younger Dryas period: Evidence from peat cellulose δC of Hani, Northeast China

Significant changes in the global atmospheric and oceanic circulation system occurred during the Younger Dryas cold period. Several researchers have demonstrated a weakening of intensity of the Indian Ocean Summer Monsoon during that period. However, the exact characteristics of the East Asian Summer Monsoon still remain vague. Here we present a late-glacial precipitation proxy record of the East Asian Summer Monsoon, based on the peat cellulose δ¹³C found in Hani, Northeast China. Both the peat cellulose record and a pollen record from Lake Sihailongwan sediment indicate an abrupt increase in precipitation in the region during the Younger Dryas period. These results support the occurrence of wet conditions in the north and of dry conditions in the south of the Chinese Mainland during that period. By examining the activity of the East Asian Summer Monsoon on an interannual timescale, we propose a theory for the anomalous precipitation distribution that we attribute to the occurrence of an El Niño-like phenomenon in the Equatorial Pacific Ocean during the Younger Dryas. In this case, the intensity of the Western Pacific subtropical high may strengthen, and its position over the western Pacific Ocean may move northward. This could cause an enhancement of the East Asian Summer Monsoon and migration of a monsoonal rainbelt towards the northern region of the Chinese mainland, resulting in a precipitation distribution of wet conditions in the north and dry conditions in the south. Therefore, this anomalous rainfall distribution should be considered to indicate the strengthening of the East Asian Summer Monsoon, in anti-phase with the Indian Ocean Summer monsoon that weakened during the same period. This agrees with the previously revealed anti-phase variations of the two monsoons during the ice-rafted debris cold events of the North Atlantic Ocean. It appears that, in relation to the abrupt temperature drop in the Northern Hemisphere on centennial to millennial time scales, anti-phase variations of the two Asian summer monsoons occurred.     

晚更新世以来呼伦湖地区孢粉植物群发展与环境变迁

呼伦湖是我国纬度最高的湖泊。晚更新世以来,由于气候冷暖干湿的多次波动,湖相及河流,风成为主的水上沉各佼替变化。通过对该区东露天煤矿沉积剖面１１３块样品进行系统孢粉百分比及浓度分析,划分出８个孢粉组合带。结合＾１４Ｃ测年数据,确定了该区２００００年以来的气候演变序列。     

Climate-related changes during the Late Glacial and early Holocene in northern Poland, as derived from the sediments of Lake Sierzywk

Reconstruction of past climate change and ecosystem response is important to correctly assess the impacts of global warming. In this study, we provide a paleoenvironmental record of in-lake and catchment changes in northern Poland during the Late Glacial and early Holocene using various biotic proxies (pollen, macrofossils and Cladocera) preserved in the lake sedimentary record. Chronology was derived from palynological correlation with a well-dated pollen sequence from nearby-lying Lake Ostrowite and some well-dated events of vegetation history in Central Europe. Pollen analysis provided information on regional climate change affecting vegetation dynamics, whereas macrofossils supplied substantial information on the response of local flora and fauna to climatic, geomorphological and limnological changes. Data were supplemented by analysis of Cladocera remains, which are of special importance because of their quick response to changes in trophic conditions and climate (especially temperature). The bottom of the sediment core reflects an initial stage of the lake formed during the late Aller?d. The Younger Dryas cooling apparently resulted in forest recession and presence of cold tolerant Cladocera species. Due to amelioration of climate at the end of the Younger Dryas and melting of ice, the lake deepened. The beginning of the Holocene was characterised by forest shrinkage and induced clear changes in local flora and fauna communities. The regional vegetation development deduced from the lake’s core is generally consistent with the vegetation history of central Europe. Due to the location of the site near the seashore (oceanic climate and western wind), signals of warming came earlier than inland and in eastern Poland.     

四万年来南海北部周边地区植被演替序列—孢粉生物群区化方法恢复古植被的尝试

就南海北部海域17940孔的孢粉资料,利用孢粉生物群区化方法和因子分析方法,对南海北部周边地区4万年以来的植被演替序列进行研究。结果表明：对于深海沉积物,在排除远距离搬运的花粉尤其是松属（Pinus L.)花粉的噪音后,可以利用孢粉生物群区化方法恢复周边大陆古植被演替序列。因子分析表明,湿度和温度的变化是影响南海北部周边大陆植被演化的主要因子。在40500－11100aBP南海北部沿海大陆地区的古植被,主要为常绿阔叶林（WAMF）,山地针叶林（MRGF）分布于低山、丘陵、而广泛出露的大陆架上则发育了以蒿属(Artemisia L.)为主的草原（STEP）景观：末次冰期时环境变化的突出特征山地针叶林（MRGF）、常绿阔叶林（WAMF）与草原（STEP）之间的频繁交替,反映了气候冷湿和温干的千年级尺度的迅速变化,可以与Heinrich事件以及Dansggard-Oscherge事件进行对比。其中在7.0m处（12700aBP)所恢复的山地针叶林（MRGF）景观反映了一次气候变冷变湿的事件,可能与新仙女木事件相对应。全新世早期和末期较多出现热带雨林（TRFO0以及热带季雨林（TSFO）景观,而全新世中期以常绿阔叶林（WAMF）为主,缺乏热带雨林（TRFO）以及热带季雨林（TSFO）景观,可能表明在全新世中期尽管温度升高,但湿度有可能降低。     

Early Holocene environmental change and the presence of Mesolithic people in the Tungelroyse Beek valley near Mildert,the Netherlands

An archaeological excavation in the Tungelroyse Beek valley revealed the remains of two red deer specimens (Cervus elaphus) of Early Mesolithic age that possibly were the victims of hunter-gatherers. The find of animal remains of this age is unique in the Netherlands. In this respect, a sediment core taken close to the remains was investigated, i.e. to reconstruct the vegetation and landscape development of the site and to find more evidence for human activity at this site during the Early Mesolithic. The sediment core shows a typical Early Holocene palynological sequence from the Younger Dryas into the Middle Atlantic, which is supported by AMS dating. The microscopic charcoal record shows peaks in fire activity during the Younger Dryas and Friesland phase, probably wildfire related. Records of spores of coprophilous fungi indicate that the Tungeroyse Beek valley was a favourable place for large herbivores (game) to visit during the investigated period. However, around the age of the oldest red deer remains, no significant peak in fire activity or spores of coprophilous fungi is visible in the investigated record. The pollen diagram does not show disturbed or open vegetation around this age either. This study therefore suggests the impact of Early Mesolithic people on their environment was very low.     

Vegetation responses to rapid climatic changes during the last deglaciation 13,500–8,000?years ago on southwest And?ya, arctic Norway

The late-glacial vegetation development in northern Norway in response to climate changes during the Aller?d, Younger Dryas (YD), and the transition to the Holocene is poorly known. Here we present a high-resolution record of floral and vegetation changes at lake Lusvatnet, south-west And?ya, between 13500 and 8000 cal b.p. Plant macrofossil and pollen analyses were done on the same sediment core and the proxy records follow each other very closely. The core has also been analyzed using an ITRAX XRF scanner in order to check the sediment sequence for disturbances or hiatuses. The core has a good radiocarbon-based chronology. The Saksunarvatn tephra fits very well chronostratigraphically. During both the Aller?d and the Younger Dryas time-periods arctic vegetation prevailed, dominated by Salix polaris associated with many typically arctic herbs such as Saxifraga cespitosa, Saxifraga rivularis and Oxyria digyna. Both periods were cold and dry. Between 12450 and 12250 cal b.p. during the Younger Dryas chronozone, the assemblage changed, particularly in the increased abundance of Papaver sect. Scapiflora and other high-Arctic herbs, suggesting the development of polar desert vegetation mainly as a response to increased aridity. After 11520 cal b.p. a gradually warmer and more oceanic climate initiated a succession to dwarf-shrub vegetation and the establishment of Betula woodland after 1,000 years at c. 10520 cal b.p. The overall late-glacial aridity contrasts with oceanic conditions in southern Norway and is probably related to sea-ice extent.     

Spatial patterns of genetic differentiation in <Emphasis Type="Italic">Brachionus</Emphasis> <Emphasis Type="Italic">calyciflorus</Emphasis> species complex collected from East China in summer

In this study, the mtDNA COI genes of 124 individuals in Brachionus calyciflorus complex were sequenced and analyzed. Overall, 84 mtDNA haplotypes were defined, and were split into three clades by the phylogenetic trees. The divergences of COI gene sequence among the three clades ranged from 11.4 to 22.5%, indicating the occurrence of three cryptic species (cryptic species 1, cryptic species 2, and cryptic species 3). Within cryptic species 3, a remarkable degree of differentiation (F _st = 0.0947) might be attributable to habitat fragmentation, restricted gene flow, and founder effect, most probably together with local adaptation. The more shared haplotypes were observed, and a non-significant correlation existed between geographic and genetic distance, suggesting that some ancestral haplotypes might be involved in a past range expansion, and as founders give a similar distribution pattern among geographic populations. The networks were also in agreement with the pattern of genetic differentiation in B. calyciflorus species complex revealed by molecular phylogeny. The nested clade analysis suggested a slight geographic structure in the network I, network II, and the highest nesting clade levels within the network III. Under the possible effect of the Younger Dryas Event, the three cryptic species might have survived in multiple relict refugia throughout the south of China. The co-occurrence of cryptic species 2 and 3 might be found in Guangzhou and Hainan due to the possible interference of the barrier and contiguous range expansion. After the Younger Dryas Event, cryptic species 3 with high colonization ability might have arrived and colonized whole habitats at first, and reduce effective gene flow among cryptic species, thus effectively increasing persistence of founder events. Cryptic species 2 might, respectively, have expanded their ranges into Wuhu and Nanjing regions only because of the probable barrier of the Yangtze River, its weak colonization abilities and the ‘priority effects’ of cryptic species 3. Cryptic species 1 distributed exclusively in Danzhou probably failed to expand its ranges into mainland China because of small population size, weaker dispersal capacity, and the barrier of the Qiongzhou Strait.     

Late-glacial and Holocene vegetation history and dynamics as shown by pollen and plant macrofossil analyses in annually laminated sediments from Soppensee, central Switzerland

The palynostratigraphy of two sediment cores from Soppensee, Central Switzerland (596 m asl) was correlated with nine regional pollen assemblage zones defined for the Swiss Plateau. This biostratigraphy shows that the sedimentary record of Soppensee includes the last 15 000 years, i.e. the entire Late-glacial and Holocene environmental history. The vegetation history of the Soppensee catchment was inferred by pollen and plant-macrofossil analyses on three different cores taken in the deepest part of the lake basin (27 m). On the basis of a high-resolution varve and calibrated radiocarbonchronology it was possible to estimate pollen accumulation rates, which together with the pollen percentage data, formed the basis for the interpretation of the past vegetation dynamics. The basal sediment dates back to the last glacial. After reforestation with juniper and birch at ca. 12 700 B.P., the vegetation changed at around 12 000 B.P. to a pine-birch woodland and at the onset of the Holocene to a mixed deciduous forest. At ca. 7000 B.P., fir expanded and dominated the vegetation with beech becoming predominant at ca. 500¹⁴C-years later until sometime during the Iron Age. Large-scale deforestation, especially during the Middle Ages, altered the vegetation cover drastically. During the Late-glacial period two distinct regressive phases in vegetation development are demonstrated, namely, the Aegelsee oscillation (equivalent to the Older Dryas biozone) and the Younger Dryas biozone. No unambiguous evidence for Holocene climatic change was detected at Soppensee. Human presence is indicated by early cereal pollen and distinct pulses of forest clearance as a result of human activity can be observed from the Neolithic period onwards.