江苏太湖平原北翼的第四纪孢粉与环境

本文根据湖北侧4个钻孔的孢粉分析,^14C和古地磁测试,并结合钙质超微化石,介形类和有孔虫所确定的海侵地层,将太湖地区的划为10个孢粉带,再参照长江下游相关资料,着重对12．7－1．5万年以来的4个孢粉带作了较深入的环境探讨,揭示出VI带（12．7－7．0万年）为常绿落叶阔叶混交林,反映温暖湿润的亚热带气候,其主要温暖阶段冬温较今高4－5度,当时湿度相对偏大,当然其中也有凉湿与干凉时段,Ⅶ带（7．0－3．0万年）为疏林草原,反映冷（半）干气候,其主要寒冷阶段年均温为8度左右,但仍存在剧烈的气候波动,Ⅷ带（3．0－2．1万年）为温性常绿落叶阔叶混交林,反映温凉湿润的季风海洋性气候,其主要温凉阶段生长季月均温比现在低约3度,其中亦有更为干冷或暖湿时期,IX带（2．1－1．5万年）为森林草原－草原或干草原植被,其极干冷阶段年均温约8度,年降雨量400mm左右。     

陇东黄土高原天然草地植被类型及特征

陇东(庆阳)黄土高原天然草地植被可划分为草甸草原区和典型草原区2个植被区域,包括温性疏灌草丛、草甸草原和典型草原3个植被型14个群系,分别是:酸枣-杠柳-蒿类温性灌草丛、蕤核-红花锦鸡儿-蒿类温性灌草丛、杠柳-蕤核-蒿类-白羊草温性灌草丛、酸枣-蒿类-白羊草温性灌草丛、酸枣-河蒴荛花-白羊草温性灌草丛、白草- 鹅观草-达乌里胡枝子-蒿类暖性灌草丛、白羊草草原、白草草原、赖草草原、蒿类-白羊草草甸草原、长芒草草原、百里香草原、铁杆蒿-茭蒿草原、毛沙芦草草原。     

3．2MaBP以来河北黄骅地区孢粉地层学与古气候变迁

依据河北省黄骅市八里庄村HB1孔孢粉、古地磁和光释光等资料,发现第四纪以来渤海西岸的古植被演变受气候变化的影响,也受沉积环境的制约.1.6-3.2 Ma BP期间河流发育时期孢粉不丰富;孢粉富集带多出现在湖相地层,而且持续时间短,孢粉贫乏带多出现在河流相沉积地层,持续时间较长;O.8-1.6 Ma BP期间植被以疏林草原为主,局部草原存在,古气候温和偏干.O.13 Ma BP以来,随着明显的古季风变化,孢粉丰富,气候序列分辨率高,可与海洋氧同位素分期对比;11 ka BP以来气候变暖湿润,为针阔叶混交林草原或沼泽草甸植被,3 ka BP之后为海退时期,气候变凉变干,植被由沼泽草甸演变为盐生草甸.尽管该孔是目前沿海平原深孔分析孢粉样品最密的钻孔,但是未能发现连续丰富的孢粉,可能与该孔位于相对较高部位,多与河流沉积环境有关;故而,平原区内并非每一个钻孔皆足以反映整个第四纪孢粉地层学的全貌.     

滦河流域及周边地区花粉与植被关系的研究

滦河流域及周边地区空气中的花粉组合基本上反映了当地的植被面貌, 与植物的花期相对应, 乔木植物的花期多在春季, 草本植物的花期多在夏秋季, 该地冬季基本上无植物开花, 冬季空气中的花粉应是当年或多年春、夏、秋季散落在地上又被风吹到空气中的表土花粉和一些外来花粉 ;表土花粉随海拔高程的降低依次出现山地草甸、针阔混交林或以针叶树为主的针阔混交林、山地灌草丛、滨海平原草甸和滨海草甸或滨海盐生草甸的等 5个花粉组合带, 分别为蒿 (Artemisia)唐松草 (Thalictrum)松(Pinus)桦 (Betula) 孢粉组合带、松桦栎 (Quercus) 蒿孢粉组合带、藜科 (Chenopodiaceae)蒿禾本科 (Gramineae)中华卷柏 (Selaginellasinensis) 孢粉组合带、藜科蒿菊科 (Com positae)香蒲 (Typha) 孢粉组合带和藜科蒿莎草科 (Cyperaceae)禾本科孢粉组合带 ;由于花粉在河水中是以悬移质颗粒被搬运, 因此在不同时期沉积物花粉组合存在着一定的差异, 其中洪水期间河水对孢粉的分选作用最为明显。     

25000年以来渤海湾西岸古环境探讨

 本文依据孢粉、微体古生物、放射性碳测年、因子分析等资料,表明25000a,BP 以来渤海湾西岸的古植被,古地理环境演变既受气候冷暖变化的影响,又受海平面变化的制约。25000—23000a,BP 为高海平面时期,古植被为森林草甸植被,23000—12000a,BP,气候冷干,为低海平面时期,以草原植被为主,前期和后期为沼泽草甸植被。12000—5000a,BP 气候温凉或温暖湿润为海平面上升时期,为阔叶林草甸或沼泽草甸植被,5000a,BP 以来,气候变凉变干,为海退时期,古植被由沼泽草甸演变为盐生草甸。     

最近12 000年来青藏高原植被的时空分布

青藏高原30个点湖泊的孢粉记录综合研究显示: 在进入全新世之前(12 ka BP以前),除最东南部外,高原从东到西均发育为荒漠草原植被.全新世早期(12.0-9.0 ka BP)高原东南部(104°-98° E)为落叶阔叶林/针阔叶混交林; 中部(98°-92° E)为草甸或灌丛草甸,再向西至80° E左右为草原植被; 全新世中期(9.0-3.2 ka BP)高原由东向西古植被依次发育为针阔混交林和硬叶阔叶林(104°-98° E)→针阔混交林(98°-94° E)→灌丛草甸(94°-92° E)→草原(92°-80° E);全新世晚期(3.2 ka BP以后)由东向西古植被依次为硬叶阔叶林→针阔混交林→草甸→草原→荒漠.     

青海湖QH85—14C钻孔孢粉分析及其古气候古环境的初步探讨

本文主要依据青海湖具有~(14)C 年龄数据的 QH 85-14C 钻孔系统孢粉分析资料,将井深4.5m 岩芯所做的孢粉图式从下至上分为五个区域性孢粉带,进而论述了青海湖区11,000年来的植被曾经历了疏林草原(11,000—10,000年 BP)、森林草原(10,000年 BP)、森林(8,000—3,500年 BP)、森林草原(3,500—1,500竿 BP)和疏林草原(1500年前至今),反映的气候序列为凉干→温湿→温干阶段。     

黑龙江省富拉尔基晚新生代孢粉分析及其意义

本文根据富拉尔基 QH70孔(井深226.07m)73块孢粉样所取得的123科属埴物孢粉,依据其孢粉组合特征,从下至上划分出七个区域性孢粉带。第Ⅰ带属晚白垩世早期,植物群具热带-亚热带的面貌,反映当时的气候热而潮湿。第Ⅱ—Ⅲ带,地质时代为晚第三纪。组合中除葇荑花序植物为主外,同时又保存较多的亚热带落叶和常绿阔叶乔木树种,气候温暖潮湿。至第Ⅲ带晚期,草本植物和半灌木已占优势,表明气温下降,变干。第Ⅳ带由蒿、藜科、禾本科、蓼等中旱生的草本及半灌木组成温性草原,气候冷干。孢粉组合特征结合热释光和磁性地层,将该区上新世和更新世界限确定为距今240万年左右。第Ⅳ—Ⅶ带属更新世,各孢粉组合具明显的差异。在Ⅴ带的早期,植被尚属草原或冻原,气候寒冷干燥,但在其晚期,则属落叶阔叶林和草原,表明气候温暖半潮湿。在Ⅵ—Ⅶ带内,草本植物占优势,但在末次冰期时,由云杉、冷杉、落叶松和桦等组成的北方针叶林曾一度繁盛在低地和平原,气候寒冷潮湿。     

25000年以来勃海湾西岸古环境探讨

本文依据孢粉,微体古生物,放射性碳测年,因子分析等资料,表明25000a,BP以来渤海湾西岸的古植被,古地理环境演变既受气候冷暖变化的影响,又受海平面变化的制约,25000－23000a,BP为高 平面时期,古植被为森林草甸植被,23000－12000a,BP气候冷干,为低海平面时期,以草原植被为主,前期和后期为沼泽草甸植,被12000－5000a,BP气候温凉或温暖湿润为海平面上升时期,为阔叶林草甸或沼泽草佃植被,5000a,BP以来,气候迹凉变干,为海退时期,古植被由沼泽草甸演为盐生草甸。     

最近12000年来青藏高原植被的时空分布

青藏高原 30个点湖泊的孢粉记录综合研究显示 :在进入全新世之前 (12kaBP以前 ) ,除最东南部外 ,高原从东到西均发育为荒漠草原植被。全新世早期 (12 .0 - 9.0kaBP)高原东南部 (10 4° - 98°E)为落叶阔叶林 /针阔叶混交林 ;中部 (98° - 92°E)为草甸或灌丛草甸 ,再向西至 80°E左右为草原植被 ;全新世中期 (9.0 - 3 .2kaBP)高原由东向西古植被依次发育为针阔混交林和硬叶阔叶林 (10 4° - 98°E)→针阔混交林 (98° - 94°E)→灌丛草甸 (94° -92°E)→草原 (92°- 80°E) ;全新世晚期 (3.2kaBP以后 )由东向西古植被依次为硬叶阔叶林→针阔混交林→草甸→草原→荒漠。     

Holocene Palynological Records in Lake Selincuo,Northern Xizang

Selincuo (31°34′–31°57′N, 88°31′–89°21′E)is one of the great lakes in northern Xizang surrounded by alpine grassland, composed mainly of Stipa purpurea, S, subssessifolia var. bassipulomosa. A 3.08 m long core has been taken from a water depth of 27 m, 3 km to the north from the lake. Palynological records of the core combined with surface sample results have revealed from the regional as well as local vegetational and environmental history since the last 12 000 a BP, a very low pollen concentration (19–209 grains/g), mainly of airborne pollen, which indicated a treeless alpine sparse vegetation. A great vegetation change took place at Ca. 9 600 a BP when alpine sparse vegetation was replaced by alpine grassland lasting until Ca. 6 000 a BP. Quite a number of tree pollen grains found in this time interval might be explained as a result of expansion of forests somewhere around the Xizang Plateau. These changes must have caused by climatic warming during the Early Holocene. During the last 6 000 years the vegetation had remained as the alpine grassland, although probably more luxurouste than before, but their was an obvious increase of arboreal pollen, such as the increase of Abies during Ca. 6 000–4 000 a BP, Picea 4 000–2 200 a BP, Pinus 2 200–1 000 a BP which indicated continuous expansion of forests growing around the plateaus. During the last 1 000 years both the concentration and proportion of the arboreal pollen decreased and those of Cypraceae pollen increased sharply. This might mean a reduction of the forests around the plateau and an expansion of swamps around the lake.     

Integrated palaeoecological and historical data in the service of fine-resolution land use and ecological change assessment during the last 1000 years in Rõuge, southern Estonia

Aims Our aim is to reconstruct decadal scale development of historical landscapes during the last 1000 years by means of fossil pollen analysis of annually laminated lake sediments, and detailed historical maps and documents. Location Lake Rõuge Tõugjärv (Estonia), a small lake with annually laminated lake sediments situated in a dense prehistoric setting. Methods The chronology of the palaeodata is based on the annual laminations supported by AMS ¹⁴C and ²¹⁰Pb dating and ¹³⁷Cs, ²⁴¹Am, and spheroidal carbonaceous particle marker horizons. The time‐scale and resolution allows fine sampling (the pollen samples generally comprise 3.5 years) and vegetation change reconstruction. Relevant source area of pollen (RSAP) of the lake was estimated, and the statistical zonation, rate of change, palynological richness, and DCA and PCA ordinations were generated on the basis of the pollen data. The historical calibration data set (maps, numerical information on population, domestic stock, farmland division, etc.) is based on archival material preserved in the Estonian Historical Archives. Results The topmost part (0–180 cm) of the sediment column of Lake Rõuge Tõugjärv, covering the last 1000 years, is visibly laminated carbonaceous gyttja. The varve chronology extends from ad 2000 to ad 1339, with a cumulative ± 9‐year error estimate. Beyond this the chronology is extrapolated using the ¹⁴C date and varve age–depth estimations. The simulation of the RSAP of Lake Tõugjärv shows that the major portion of the pollen loading originating from local vegetation is derived from plants growing within 2000 m of the sampling site. The pollen record divides into five statistically significant subgroups, which fall on the PCA plot into three clusters reflecting the general openness–closedness of the landscape. During the period between ad 1000 and 1200 (RT 1) the Rõuge area was generally wooded with birch, spruce and pine forests. The advancement of extensive farming gradually opened up the landscape between ad 1200 and 1650 (RT 2 and RT 3). The maximum openness of the landscape was reached between ad 1650 and 1875 (RT 4), with the most open period in the late eighteenth century. Historical maps from 1684 and 1870–99 and available quantitative data on population, domestic stock, farmland division, etc. show the same trend. The pollen data covering the last 125 years, and maps from 1935 and 1995, show the reduction of arable land in RSAP of the lake under investigation and the reduction of open land to an extent comparable with the end of the seventeenth century. Main conclusions The formation and development of the cultural landscape at Rõuge over the last 1000 years is characterized by rapid changes in floristic richness and rates of vegetation change attributed to certain historic processes in the RSAP. Five phases of landscape and social development are clearly distinguished during the last 1000 years. The decadal scale vegetation response to human‐induced forcing agrees with historical maps and documents and could be used for past landscapes prior to the period with solid historical data.     

The Holocene vegetation history of northern West Jutland, Denmark

Holocene sediments of three closed Danish lake basins (Solsø, Skånsø, Kragsø) were used for the inference of post-glacial vegetational dynamics in former heathland areas in northern West Jutland, Denmark. The sites were selected to represent the major geomorphological units of West Jutland. The Holocene history of each lake basin was investigated by mapping of sediment distribution, analysis of loss-on-ignition, coarse inorganic matter, humus content, mineral magnetics, δ¹³C, pollen and selected other microfossils. These techniques were supplemented by plant macrofossil analysis at one site. Holocene terrestrial vegetational development was inferred at each site from analyses of pollen and microscopical charred particles. Chronologies were provided by numerous ¹⁴C dates. Stratigraphies of wet ground and terrestrial pollen and spore types were zooned by stratigraphically constrained cluster analysis. Based on the resultant site pollen asemblage zones (site PAZ), regional PAZ were proposed. Using modern analogues, Holocene floristic richness was estimated from pollen richness in the microfossil assemblages. The results support the hypothesis that disturbance is one of the most important mechanisms behind the maintenance of floristic richness. In particular, the response of estimated floristic richness to the intensity of vegetational fires followed the predictions of the Intermediate Disturbance Hypothesis. A period of elevated palynological richness and inferred vegetational disturbance was identified at all sites between 6000 and 5200 BC (calendar years). Using correspondence analysis (CA), the major gradient in the terrestrial pollen sequences was identified as a light-shade gradient, and CA first axis sample scores were used as a supplement to standard AP/NAP pollen ratios as an indicator of the shade-tolerance/light-demand of Holocene terrestrial plant communities. In spite of different vegetational developments since 4000 BC, the timing of major changes towards more light-demanding vegetation types were broadly synchronous at the three sites. Using chord distance as a dissimilarity index, rates of palynological change suggest that the interval between 8000 and 7500 BC (calendar years) was the period of most rapid vegetational change during the Holocene, both in terrestrial as well as lacustrine ecosystems. While climatic forcing of the rapid events around 8000 BC is hypothesised, the synchronous timing of relatively rapid inferred change in lake and terrestrial vegetation around AD 600 may reflect changes in climate as well as in land-use. Reducdancy analysis was used to develop a model between fire intensity (inferred from microscopical charred particles) and vegetational response, as reflected by pollen assemblages. Formulated at one site and tested at the two other sites, the model explains regional Calluna-heathland expansions as a result of vegetational burning. Similarly, declines in heathland cover are explained by lack of maintenance by fire. Regional vegetational development in northern West Jutland is reconstructed and special consideration is given to heathland history. The Holocene heathland development is interpreted as resulting from its importance for grazing. It is hypothesized that on poor soils, Calluna-dominated heathland was a better grazing resource than grass-dominated pasture, due to the winter-grazing offered by Calluna and the low palatibility of dominant grasses on poor soils. This hypothesis is relevant for the explanation of the variation in timing of heathland expansions on the different soil types represented by the study sites.     

The Holocene vegetation history of northern West Jutland, Denmark

Holocene sediments of three closed Danish lake basins (Solsø, Skånsø, Kragsø) were used for the inference of post-glacial vegetational dynamics in former heathland areas in northern West Jutland, Denmark. The sites were selected to represent the major geomorphological units of West Jutland. The Holocene history of each lake basin was investigated by mapping of sediment distribution, analysis of loss-on-ignition, coarse inorganic matter, humus content, mineral magnetics, δ¹³C, pollen and selected other microfossils. These techniques were supplemented by plant macrofossil analysis at one site. Holocene terrestrial vegetational development was inferred at each site from analyses of pollen and microscopical charred particles. Chronologies were provided by numerous ¹⁴C dates. Stratigraphies of wet ground and terrestrial pollen and spore types were zooned by stratigraphically constrained cluster analysis. Based on the resultant site pollen asemblage zones (site PAZ), regional PAZ were proposed. Using modern analogues, Holocene floristic richness was estimated from pollen richness in the microfossil assemblages. The results support the hypothesis that disturbance is one of the most important mechanisms behind the maintenance of floristic richness. In particular, the response of estimated floristic richness to the intensity of vegetational fires followed the predictions of the Intermediate Disturbance Hypothesis. A period of elevated palynological richness and inferred vegetational disturbance was identified at all sites between 6000 and 5200 BC (calendar years). Using correspondence analysis (CA), the major gradient in the terrestrial pollen sequences was identified as a light-shade gradient, and CA first axis sample scores were used as a supplement to standard AP/NAP pollen ratios as an indicator of the shade-tolerance/light-demand of Holocene terrestrial plant communities. In spite of different vegetational developments since 4000 BC, the timing of major changes towards more light-demanding vegetation types were broadly synchronous at the three sites. Using chord distance as a dissimilarity index, rales of palynological change suggest that the interval between 8000 and 7500 BC (calendar years) was the period of most rapid vegetational change during the Holocene, both in terrestrial as well as lacustrine ecosystems. While climatic forcing of the rapid events around 8000 BC is hypothesised, the synchronous timing of relatively rapid inferred change in lake and terrestrial vegetation around AD 600 may reflect changes in climate as well as in land-use. Reducdancy analysis was used to develop a model between fire intensity (inferred from microscopical charred particles) and vegetational response, as reflected by pollen assemblages. Formulated at one site and tested at the two other sites, the model explains regional Colluna-heathland expansions as a result of vegetational burning. Similarly, declines in heathland cover are explained by lack of maintenance by fire. Regional vegetational development in northern West Jutland is reconstructed and special consideration is given to heathland history. The Holocene heathland development is interpreted as resulting from its importance for grazing. It is hypothesized that on poor soils, Calluna-dominated heathland was a better grazing resource than grass-dominated pasture, due to the winter-grazing offered by Calluna and the low palatibility of dominant grasses on poor soils. This hypothesis is relevant for the explanation of the variation in timing of heathland expansions on the different soil types represented by the study sites.     

From ice age to modern: a record of landscape change in an Andean cloud forest

Aim To investigate the palaeoecological changes associated with the last ice age, subsequent deglaciation and human occupation of the central Andes. Location Lake Pacucha, Peruvian Andes (13°36′26″ S, 73°19′42″ W; 3095 m elevation). Methods Vegetation assemblages were reconstructed for the last 24 cal. kyr bp (thousand calibrated ¹⁴C years before present), based on pollen analysis of sediments from Lake Pacucha. An age model was established using ¹⁴C accelerator mass spectrometry dates on bulk sediment. Fossil pollen and sedimentological analyses followed standard methodologies. Results Puna brava replaced the Andean forest at the elevation of Lake Pacucha at the Last Glacial Maximum (LGM). Deglaciation proceeded rapidly after 16 cal. kyr bp , and near‐modern vegetation was established by c. 14 cal. kyr bp . The deglacial was marked by the range expansion of forest taxa as grassland taxa receded in importance. The mid‐Holocene was marked by a lowered lake level but relatively unchanged vegetation. Quinoa and maize pollen were found in the latter half of the Holocene. Main conclusions Temperatures were about 7–8 °C colder than present at this site during the LGM. The pattern of vegetation change was suggestive of microrefugial expansion rather than simple upslope migration. The mid‐Holocene droughts were interrupted by rainfall events sufficiently frequent to allow vegetation to survive largely unchanged, despite lowering of the lake level. Human activity at the lake included a 5500‐year history of quinoa cultivation and 3000 years of maize cultivation.     

Late Quaternary vegetation history at Stracciacappa (Rome, central Italy)

The pollen diagram from Stracciacappa (Sabatini volcanic complex, Rome) provides a record of vegetational and climatic change spanning the last 60000 years, which is the time since when volcanic activity in the crater came to an end. The chronological framework of the sediment core is set by five AMS and three conventional radiocarbon dates; the mean sedimentation rate obtained by radiocarbon measurements was used to extrapolate the age of the record beyond the reach of ¹⁴C dating. The sequence from Stracciacappa provides results of fundamental importance for the understanding of the vegetational changes which occurred during the last pleniglacial period in central Italy, and it can be considered as a reference pollen record for the regional biostratigraphic characterization of this period. The site shows a high climatic sensitivity, particularly highlighted by the development of some pleniglacial oscillations with woodland, which interrupted the succession of steppe and grassland vegetational formations typical of the glacial periods. Unfortunately, due to sedimentation problems and alteration of the top level sediments, the Holocene is only recorded in part. Only for one millennium, from ca. 8300 to 7200 uncalb.p., was a real forest expansion characterized by over 90% arboreal pollen found.     

Vegetation changes in Empakaai Crater, northern Tanzania, at 14,800–9300 cal yr BP

Vegetation changes are documented from a well-dated pollen record from Lake Emakat, Empakaai Crater, northern Tanzania. This pollen record includes the time interval covering the Pleistocene/Holocene transition, analysed at a resolution interval averaging 200 yr. Around the crater lake, an Hagenia-forest development starting at 14,500 cal yr BP lasted until 13,000 cal yr BP. A change in vegetation, indicated by an increased proportion of Nuxia congesta in the forest and Artemisia in the afro alpine grassland after 13,000 cal yr BP, corresponds in time to the Northern Hemisphere's Younger Dryas cooling. Grasses and sedges increased at  10,100 cal yr BP, indicating a significant increase in local pollen possibly attributed to lowered lake level, related to drier conditions. Although the Empakaai pollen record documents continuous forest conditions, from 14,500 to 10,100 cal yr BP, the variation in the proportion of forest components seem to respond to environmental changes at the millennium scale.     

Palynological investigations into the Late Pleistocene and Holocene history of vegetation and settlement at the Löddigsee, Mecklenburg, Germany

A Late Pleistocene and Holocene sediment core from the nowadays terrestrialised portion of the Löddigsee in Southern Mecklenburg, Germany was palynologically investigated. The lake is situated in the rarely investigated Young moraine area at the transition from the Weichselian to the Saalian glaciation. The high-resolution pollen diagram contributes to the establishment of the north-eastern German Late Pleistocene pollen stratigraphy. The vegetation distribution pattern after the end of the Weichselian is in good agreement with other studies from North-eastern Germany, but also has its own characteristics. The Holocene vegetation development reveals features from the north-eastern and north-western German lowlands. A special focus was laid on the environmental history of the two settlements on an island within the lake (Late Neolithic and Younger Slavic period), which were preserved under moist conditions. Both settlements were constructed during a period of low lake level. Although there is evidence of agriculture in the area during the respective periods, the two island settlements seem to have served other purposes.     

西藏扎布耶盐湖晚第四纪孢粉植物群的初步研究

扎布耶盐湖位于西藏青藏高原腹地。通过该湖ＺＫ２钻孔的孢粉分析,揭示了约３６０００ａＢ．Ｐ．以来扎布耶地区的气候和湖盆演变。约在３６０００－３３０００ａＢ．Ｐ．,扎布耶地区为森林草原,气候冷、湿;约３３０００－３００００ａＢ．Ｐ．,为灌丛草原,气候温、干;约３００００－２７５００ａＢ,Ｐ．为干旱草原,气候偏暖、湿;约１８０００－１２０００ａＢ．Ｐ．,为干旱草原,环境寒冷,干燥;约１２０００－４０００ａＢ．Ｐ．,扎布耶地区各类草本植物繁茂,气候偏温、干。另外,根据水生藻类化石群的分析,自３６０００ａＢ．Ｐ以来,扎布耶盐湖有三次湖进、淡水湖期,同时也有三次湖退事件。     

Climate-lake interactions recorded in varved sediments from a Swedish boreal forest lake

A 1100-year long record of lake ecosystem response to climate and catchment change with precise chronological control is reported. Diatom and pollen assemblages of an annually laminated (varved) sediment from a northern Swedish lake (Kassjön, Våsterbotten) were used as records of lake diatom communities and catchment vegetation. These data were compared with summer temperature estimates based on tree-ring records of the same geographical area to identify the effects of climate change and catchment disturbance on diatom assemblages in the lake. In a canonical ordination, 23% of the variability in the total diatom assemblages for the period AD1040–1804 was accounted for by changes in pollen data which reflect agricultural development in the catchment. Diatom species richness, however, exhibited a stronger relationship with summer temperature and, significantly, declined with the lower temperatures associated with the Little Ice Age minimum (early 17th century). Summer temperature accounted for 23% of the variability in diatom species richness 20 years later. The mechanism behind this time-lag is unclear, but may be related to catchment-mediated effects, given recent evidence for lags in the response of boreal-forest vegetation regeneration cycles to climatic variability. These results suggest that climate-related effects on lakes occurring over medium timescales can be resolved in lake sediments. Moreover, it is possible to identify these effects despite cultural-related signals, but as the latter become more extreme in the late 20th century the climate signal is obscured.