Palynological record during the Pleistocene (between 1.05 Ma and 0.36 Ma) from ODP1144, northern South China Sea

This paper presents the pollen record from the lower section of ODP1144 (depth 501.3-225.7 m, ca. 1.05-0.36 Ma). Two pollen zones (PA and PB) and eleven pollen subzones are recognized. Within zone PB, the 11 pollen subzones (PB21-11) are defined according to the pine, fern and herb variations, and are equivalent to the marine isotope stages 21-11 (MISs 21-11). The interglacial periods are typified by an increase in pine pollen and fern spores, and a decrease in herbaceous pollen, while the patterning during the glacial periods is just the opposite. During the interglacial periods, pollen assemblages were dominated by pine similar to those of the present day, suggesting that the paleoenvironment of the interglacial periods was similar to that of the present day, whereas the glacial periods are marked by an increase in herbaceous pollen, mainly Gramineae and Cyperaceae, indicating that grassland covered the exposed continental shelf when sea level declined. Increased Artemisia percentages and the highest     

Records of natural fire and climate history during the last three glacial-interglacial cycles around the South China Sea Charcoal record from the ODP 1144

The history of natural fire and its relationship to climate during the last three glacial-interglacial cycles in the Southern coast areas of China and the northern continental shelf of the South China Sea (SCS) are discussed based on the statistic study of charcoal particles and associated pollen data from ODP 1144 Site (20° 3′N, 117° 25’E, 2037 m in water depth). According to the results of the charcoal and pollen study, the sediments from the upper 225 m are divided into 8 zones (C1–C8), which might be correlated with the Marine Isotope Stage 1–8 (MIS1-8) respectively. Our study indicates that during the last glacial period (MIS2, 4), the influx of charcoal particle was much higher than that from the interglacial period, suggesting strong occurrence of natural fire and dry climate. During MIS 6 and MIS 8 (C6, C8), although the influx of fine charcoal particles was quite high, the influx of the coarse and medium charcoal particle were much low, which might be due to the smaller source area of fire probably resulting from the limited exposure of the continental shelf before MIS5. During the interglacial period (MIS1, 5, 7), the influxes of charcoal particles were much lower, implying dropping of intensity of the natural fire and then a humid climate. Another reason is that the continental shelf was submerged into the sea during the interglacial periods, and the source areas of fire were reduced then. Although the influx of the fine charcoal particles was much lower during MIS3, the influx of the coarse and medium charcoal particles were almost equal to those of MIS4 (C4), which suggests that the intensity of the natural fire remained quite high and the climate was considerably dry during that period.     

Records of natural fire and climate history during the last three glacial-interglacial cycles around the South China Sea Charcoal record from the ODP 1144

The history of natural fire and its relationship to climate during the last three gla cial-interglacial cycles in the Southern coast areas of China and the northern continental shelf of the South China Sea (SCS) are discussed based on the statistic study of charcoal particles and associated pollen data from ODP 1144 Site (20° 3′N, 117° 25′E, 2037 m in water depth). Accord ing to the results of the charcoal and pollen study, the sediments from the upper 225 m are divided into 8 zones (C1-8), which might be correlated with the Marine Isotope Stage 1-8 (MIS1-8)respectively. Our study indicates that during the last glacial period (MIS2, 4), the influx of charcoal particle was much higher than that from the interglacial period, suggesting strong occurrence of natural fire and dry climate. During MIS 6 and MIS 8 (C6, C8), although the influx of fine charcoal particles was quite high, the influx of the coarse and medium charcoal particle were much low,which might be due to the smaller source area of fire probably resulting from the limited exposure of the continental shelf before MIS5. During the interglacial period (MIS1, 5, 7), the influxes of charcoal particles were much lower, implying dropping of intensity of the natural fire and then a humid climate. Another reason is that the continental shelf was submerged into the sea during the interglacial periods, and the source areas of fire were reduced then. Although the influx of the fine charcoal particles was much lower during MIS3, the influx of the coarse and medium charcoal par ticles were almost equal to those of MIS4 (C4), which suggests that the intensity of the natural fire remained quite high and the climate was considerably dry during that period.     

A~200 ka pollen record from Okinawa Trough:Paleoenvironment reconstruction of glacial-interglacial cycles

Pollen analysis was carried out on the Core MD982194 of 29.78 m retrieved from the Middle Okinawa Trough which was dated as old as~200 ka BP.The results revealed that pollen assemblages mainly presented an alternation of coniferous and herb pollen.The coniferous saccate pollen,principally Pinus and Tsuga,predominated in most parts of the core,especially highlighted in the interstadial stages including MIS 1,3,5 and MIS7,whereas the herb pollen significantly increased in the glacial periods.Thus the pollen flora and their percentages showed the sensitive changes under the influence of ice volume during the glacial and interglacial periods.Our record from this core has first documented that the percentage of Cyperaceae was extremely high in the glacial stages with a notable increase in Artemisia,Gramineae,Asteraceae,Chenopodiaceae,and freshwater algae,which can be used as a proxy for sea-level change at the study site because of their close negative correlation of the orbital-scale changes in sea level.The distance between the continental coastline and the Okinawa Trough has deeply shortened due to the sea-level drop in the LGM.As a result,the sediment materials from Yangtze River were extensively deposited on the flat,exposed continental shelf owing to the rapid decline of river flow speed,leading to that pollen grains from Okinawa Trough are derived mainly from the flat coastal vegetation of exposed continental shelf at glacial stages.Changes of pollen assemblage were consistent with the variation of temperature and humidity,which showed that the percentage of arboreal pollen was highly augmented at MIS 7,5 and MIS 1,corresponding to the strengthening of the East Asian summer monsoon and increasing of rainfall.Moreover,the peak of Pinus percentage in MIS 5.3,5.1 and MIS 3.3 may be closely linked by orbital and sub-orbital cycles of solar radiation and monsoonal variability.The present study of core MD981294 implied lower temperature and precipitation during the lowest sea-level stage(LGM),and more visibly testified that the vegetation of the flat plain on the exposed continental shelf was dominated by intrazonal communities such as halophyte grasslands and freshwater wetlands instead of zonal steppe or semi-arid desert.All above evidence demonstrated that the fundamental changes of pollen assemblage and their origins in Okinawa Trough since~200 ka BP were affected by combine factors including the coastline position and climate fluctuation.Moreover,the substantial shortening of distance between shoreline and the Okinawa Trough driven by orbital insolation cycles was clearly indicated by the pollen spectra,whereas the source-area climate signal of the pollen record was largely weakened.     

Evidence for natural fire and climate history since 37 ka BP in the northern part of the South China Sea

The history of natural fire since 37 kaBP and its relationship to climate for the northern part of the South China Sea are revealed from the statistic study of charcoal particles and associated pollen data from deep sea core 17940 (20° 07’N, 117° 23’E, 1 727 m in water depth). Our study indicates that, during the last glaciation, the concentration of charcoal and the ratio of con centration between charcoal and terrestrial pollen are much higher than that of the Holocene. This can be explained as the relatively high strength and frequency of natural fire during glaciation which is probably due to the drier climate; during the Last Glacial Maximum (LGM), the substantial rising of the concentration of large and medium charcoal particles probably suggests the local source area of the natural fires, i.e. the exposed continental shelf; moreover, the correlation between charcoal concentration with different size and pollen percentage may elucidate different transport dynamics. During the glacial time, almost all the peak concentrations of small particles correspond with the peak pollen percentage ofArtemisia, an indicator of comparatively dry climate, while for large particles, their concentrations always lag behind small particles and thus change with pollen percentage of montane conifers implying relatively cold and humid climate. So, it is possible to assume that small particles reflect regional emissions under drier climate and were brought over by strengthened winter monsoon. When the climate became relatively humid, the increasing precipitation carried the large particles accumulated on continental shelf before under arid condition to the studied area.     

A high-resolution history of vegetation and climate history on Sunda Shelf since the last glaciation

This paper presents 16500-year-long high-resolution pollen and spore records from sediments of core 18287 on the continental slope of the southern South China Sea. In the period of 16.5―13.9 ka B.P., the low-mountain rainforest dominated the continental slope of the South China Sea. And in the period of 13.9―10.2 ka B.P., the lowland rainforest and ferns expanded greatly, while the low-mountain rainforest shrank, which indicated a warming at the last deglaciation. Also during this period, the pollen sedi-mentation rates reduced sufficiently. This might imply a rise of the sea level and therefore the sub-mergence of the shelf, resulting in the broadening of the distance between the source area and the slope. After 10.2 ka B.P, decreasing of the fern indicates the early Holocene (10.2―7 ka B.P.) is a cold period, while the increasing of fern marks the rising temperature (7―3.6 ka B.P.).     

An abrupt cooling event early in the last interglacial in the northern South China Sea

The high-resolution quantitative analysis of the planktonic foraminifera and the δ¹⁸O records of the section between 96.49– 137.6 mcd at ODP Site 1144 on the continental slope of northern South China Sea reveals an abrupt cooling event of sea surface temperature (SST) during the last interglacial (MIS 5.5, i.e. 5e). The dropping range of the winter SST may come to 7.5°C corresponding to 1.2‰ of the δ¹⁸O value of sea surface water. This event is comparable with those discovered in the west Europe and the northern Atlantic Ocean, but expressed in a more intensive way. It is inferred that this event may have been induced by middle- to low-latitude processes rather than by polar ice sheet change. Since the Kuroshio-index speciesPulleniatina obliquiloculata displayed the most distinct change at the event, it may also be related to the paleoceanographic change of the low-latitude area in the western Pacific Ocean. This event can be considered as one of “Younger Dryas-style coolings” and is indicative of climate variability of the last interglacial stage.     

Organic carbon isotope and molecular fossil records of vegetation evolution in central Loess Plateau since 450 kyr

Significant uncertainties remain regarding the temporal evolution of natural vegetation during the Quaternary, and drivers of past vegetation change, on the Chinese Loess Plateau (CLP). This study presents analyses of total organic carbon isotopic composition (TOC) and n-alkane ratios (C31/C27) from the Lingtai loess-palaeosol sequence on the central CLP over the last 450 kyr. The results demonstrate that the vegetation in this region comprised a mix of C₃ and C₄ plants of herb and woody growth-form. C₃ plants dominated for most of the last 450 kyr, but this did not lead to extensive forest. C₃ woody plants were more abundant in MIS9 (S3 period) and MIS5 (S1 period) during warm and humid climate conditions. Herbs increased in the region since 130 kyr, possibly as a result of increased aridity. On the orbital timescales, there was a reduction of C₃ herbal plants in MIS11 (S4) than in MIS12 (L5), and in Holocene than in the last glacial period. Our isotope and n-alkane proxy records are in agreement with Artemisia pollen changes in the region, which is/was the dominant species in this area and varying due to different heat and water conditions between glacial and interglacial periods. Though the climate in MIS1 (S0) was similar to that in MIS11 (S4), a significant increase in woody plants during the Holocene suggests the impact of human activities and ecological effects of changes in fire activity.     

Quaternary biogenic opal records in the South China Sea: Linkages to East Asian monsoon, global ice volume and orbital forcing

Particulate fluxes investigated in the central South China Sea (SCS) during 1993―1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470―900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420―450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The vari- ability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ 18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and temporal variations.     

Microgastropod records in paleoceanographical environment of southern shelf of South China Sea since 14 ka

Very diversified and abundant benthic microgastropods and planktonic microgastropods (pteropods) from core NS93-12-25 could provide a glance of change of the sea level in the south continental shelf of the South China Sea since last 14 ka. Research shows that general sea level changes of this sea area were rising and later rising after a short period of falling in this period. In the range from the bottom of the core to the core depth of 200 cm, individuals in big size are common in microgastropods and Turritella filiola is very rich, signifying the environment of the inner continental shelf in the last deglaciation stage. In the core depth range of 200–150 cm the continuously getting light of the δ¹⁸O, the regularly decreasing of the percentage content of T. filiola and the high diversification of microgastropods indicate the rising of the sea level. Especially at the core depth range of 175–150 cm the pteropods became dominant, making sure the fact that the high sea level possibly occurred in the early Holocene. Channels of surrounding straits connecting the adjacent sea thus were opened. But at the core depth of about 100 cm T. filiola became very rich again. This possibly implies that there was a short term of the sea level falling, resulting in the temporal closure of the channels. In the core depth range of 55–50 cm the Scaliola’s representatives relatively develop and this may be inferred to the cooling of climate.     

Instability characteristics of the East Asian Monsoon recorded by high-resolution loess sections from the last interglacial (MIS5)

The selection of high-resolution loess sections is needed in order to determine the climatic variability of the East Asian Monsoon during the last interglacial. Two sequences of S1 on the eastern and west-ern sides of the Liupan Mountain were both composed of five paleosol layers and four loess layers,indicating that there were five strong summer monsoon events and four strong winter monsoon events in MIS5. This corresponds with other records of the East Asian Monsoon,along with NGRIP and the North Atlantic records,implying that the climate of the Northern Hemisphere was very instable during the last interglacial. Two layers of paleosols and one layer of loess had developed during MIS5a and MIS5c. Compared with MIS5e,the climate in MIS5a and MIS5c fluctuated more intensively on a millen-nial scale,whereas the climate was relatively stable in MIS5e.     

Late Quaternary deformation history of the volcanic edifice of Panarea,Aeolian Arc,Italy

A series of raised palaeoshorelines is documented along the emergent coastal slopes of Panarea and surrounding islets at elevations of 115 (palaeoshoreline Ia) and 100 m a.s.l. (Ib), 62.5 m (II), 35 m (III), 12 m (IV), 10–12 (Va) and 5 m (Vb). According to stratigraphic constraints and cross-cutting relationships, these palaeoshorelines are correlated with discrete high sea-level stillstands during marine oxygen-isotope stages (MIS) 5e, 5c, 5a and 3. Coastal elevation changes suggest the occurrence of a long-term, sustained uplift trend of the volcanic edifice since the last interglacial (last 124 ka). The uplift rates are not constant but display a progressive deceleration from maximum values of 1.5–1.58 m/ka, in the period between 124 and 100 ka, down to the lowest values of 0.66–0.69 m/ka, which tend to be constant starting from 81 ka BP. The long-term deformation pattern of Panarea suggests that a transitory, volcano-related component of uplift interplayed with the regional tectonic component affecting the sub-volcanic basement, which has undergone a persistent and widespread uplift since the mid-Pleistocene. The volcano-related component of uplift, prevailing between 124 and 100–81 ka, is interpreted as the result of visco-elastic deformation mechanisms which characterize the progressive re-equilibration of the shallow magmatic system following the incoming quiescence of the volcanic edifice. The long-term uplift values at Panarea are higher than in the main portion of the western-central Aeolian Arc, where a mean uplift rate of 0.34 m/ka was estimated since the last interglacial (last 124 ka). Such a pattern of deformation on a regional scale may be a response to active deformation processes connected with the southeastward rollback of the subducting Ionian slab which is still active only in correspondence with the eastern sector of the Aeolian Arc (including Panarea). In the short-term, a localized submergence trend has been documented at the nearby islet of Basiluzzo for the last 2,000 years, likely connected to neo-tectonic movements along main NE–SW trending faults.     

Dust pollen distribution on a continental scale and its relation to present-day vegetation along north-south transects in east China

A series of dust pollen samples was collected along N-S transects in east China (18°N to 53°N latitudes). Sample sites extend from the cold-temperate zone in the north to the tropical region in the south. Pollen taxa characterize each region and reflect the natural and devastated vegetation as well as corre- sponding climatic zones. The quantitative pollen data can be used to estimate the spatial distribution of planted and introduced species. Valuable information of human disturbance of the natural forest is evaluated by quantitative comparison between dust pollen and in-situ pollen of protected forest. In addition, percentages of grass pollen vary regularly from north to south that is consistent with spatial distribution of net primary productivity in east China. Among all grasses, Artemisia and the Gramineae carry the clearest signal: their ratio increases northwards and therefore represent a suitable and con- venient tool for palaeoclimate reconstructions.     

Variability of dense water formation in the Ross Sea

This paper presents results from a model study of the interannual variability of high salinity shelf water (HSSW) properties in the Ross Sea. Salinity and potential temperature of HSSW formed in the western Ross Sea show oscillatory behaviour at periods of 5–6 and 9 years superimposed on long-term fluctuations. While the shorter oscillations are induced by wind variability, variability on the scale of decades appears to be related to air temperature fluctuations. At least part of the strong decrease of HSSW salinities deduced from observations for the period 1963–2000 is shown to be an aliasing artefact due to an undersampling of the periodic signal. While sea ice formation is responsible for the yearly salinity increase that triggers the formation of HSSW, interannual variability of net freezing rates hardly affects changes in the properties of the resulting water mass. Instead, results from model experiments indicate that the interannual variability of dense water characteristics is predominantly controlled by variations in the shelf inflow through a sub-surface salinity and a deep temperature signal. The origin of the variability of inflow characteristics to the Ross Sea continental shelf can be traced into the Amundsen and Bellingshausen Seas. The temperature anomalies are induced at the continental shelf break in the western Bellingshausen Sea by fluctuations of the meridional transport of circumpolar deep water with the eastern cell of the Ross Gyre. In the Amundsen Sea, upwelling due to a persistently cyclonic wind field carries the signal into the surface mixed layer, leading to fluctuations of the vertical heat flux, anomalies of brine release near the sea ice edge, and consequently to a sub-surface salinity anomaly. With the westward flowing coastal current, both the sub-surface salinity and deep temperature signals are advected onto the Ross Sea continental shelf. Convection carries the signal of salinity variability into the deep ocean, where it interacts with modified circumpolar deep water upwelled onto the continental shelf as the second source water mass of HSSW. Sea ice formation on the Ross Sea continental shelf thus drives the vertical propagation of the signal rather than determining the signal itself.     

黑龙江省连环湖孢粉记录揭示的约220年的环境变化与人类活动

通过210Pb测年建立年代标尺,利用黑龙江省连环湖阿木塔泡高分辨率的孢粉记录,探讨了研究区约220年的环境变化与人类活动.研究表明,1790-1820 AD期间,植被类型可能是以禾本科为主的草甸草原植被,沙地类型以固定沙地为主,气候相对较凉湿或环境几乎不受人类活动的破坏,湖泊营养较丰富.1820-1930 AD期间,草...     

吉兰泰盐湖沉积物孢粉记录的季风边缘区全新世气候演化

全新世气候具有不稳定性,且存在着区域差异,在季风边缘区尤为显著.因此,本研究选取季风边缘区吉兰泰盐湖沉积物的孢粉记录并结合AMS14C测年结果,对该地区全新世的古植被演化及古气候变化历史进行了重建.结果表明,在全新世阶段,该地区植被类型未发生变化,以干旱的荒漠植被为主.早全新世(10.5 8.5 cal ka BP),以蒿属孢粉为主,伴随出现少量藜科、禾本科及麻黄属孢粉,蒿藜比(A/C比值)相对稳定(4.11左右),指示全新世早期气候逐步转湿的过程,在8.5 cal ka BP,蒿属孢粉数量下降且被藜科孢粉取代,指示一次明显气候干旱事件;中全新世(8.5 3.5 cal ka BP),蒿属孢粉含量增加及藜科孢粉含量降低,A/C比值在7.1 cal ka BP左右达到峰值,指示该地区中全新世气候最为湿润;晚全新世(3.5 cal ka BP至今),藜科孢粉含量增加且超过早全新世,A/C比值低至3.66,区域呈现明显的干旱化趋势.此外,结合吉兰泰盐湖沉积物矿物组成结果,发现中全新世湖泊沉积物中,钙芒硝大量出现,一定程度上指示降水量增多所带来的淡水注入,与孢粉指标指示该阶段湿润的结果一致.通过区域对比,发现吉兰泰地区在全新世时期的气候演化模式与东亚季风区具有较好的一致性,表明该地区受到东亚夏季风的影响较大,尤其是在中全新世,东亚夏季风增强,带来较多的降水,气候湿润.     

Spatial patterns of vegetation and climate in the North China Plain during the Last Glacial Maximum and Holocene climatic optimum

Reconstructing the spatial patterns of regional climate and vegetation during specific intervals in the past is important for assessing the possible responses of the ecological environment under future global warming scenarios. In this study, we reconstructed the history of regional vegetation and climate based on six radiocarbon-dated pollen records from the North China Plain. Combining the results with existing pollen records, we reconstruct the paleoenvironment of the North China Plain during the Last Glacial Maximum(LGM) and the Holocene Climatic Optimum(HCO). The results show that changes in the regional vegetation since the LGM were primarily determined by climatic conditions, the geomorphic landscape and by human activity.During the LGM, the climate was cold and dry; mixed broadleaf-coniferous forest and deciduous-evergreen broadleaf forest developed in the southern mountains, and cold-resistant coniferous forest and mixed broadleaf-coniferous forest were present in the northern mountains. The forest cover was relatively low, with mesophytic and hygrophilous meadow occupying the southern part of the plain, and temperate grassland and desert steppe were distributed in the north; Chenopodiaceae-dominated halophytes grew on the exposed continental shelf of the Bohai Sea and Yellow Sea. During the HCO, the climate was warm and wet;deciduous broadleaf forest and deciduous-evergreen broadleaf forest, with subtropical species, developed in the southern mountains, and deciduous broadleaf forest with thermophilic species was present in northern mountains. Although the degree of forest cover was greater than during the LGM, the vegetation of the plain area was still dominated by herbs, while halophytes had migrated inland due to sea level rise. In addition, the expansion of human activities, especially the intensification of cultivation,had a significant influence on the natural vegetation. Our results provide data and a scientific basis for paleoclimate modelling and regional carbon cycle assessment in north China, with implications for predicting changes in the ecological environment under future global warming scenarios.     

Pollen-inferred vegetation and environmental changes in the central Tibetan Plateau since 8200 yr BP

The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200 cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200–6500 cal. yr BP, especially 8200–7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe dominated during the periods of 6000–4900, 4400–3900, and 2800–2400 cal. yr BP. The steppe decreased gradually and the meadow expanded during the period of 4900–4400 cal. yr BP. Three century-scale drought events occurred during 5800–4900, 4400–3900 and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal. yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present level. However, the cold climate between 700–300 cal. yr BP likely corresponds to the Little Ice Age. Supported by Chinese Academy of Sciences 100 Talents Project (Grant No. 29082762), National Natural Science Foundation of China (Grant Nos. 40671196, 40372085, 49371068, 49871078), and U.S. National Science Foundation (Grant Nos. ATM-9410491, ATM-008194)     

Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China

Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA.     

A high-resolution late Pleistocene record of pollen vegetation and climate change from Jingning, NW China

During the late Pleistocene, a number of climatic fluctuations such as the Heinrich events were recorded in the climatic proxies in the Loess Plateau and in North China[1―7]. Most of these records were based on geophysical and geochemical evidence[1―4]. Therefore, more biologic evidence is necessary for explaining the regional ecosystems in response to climatic change in the Loess Plateau during this period since pollen re-cords in other areas presented strong evidence to cli-matic fluctu…