长江下游巢湖9870cal.aB.P.以来孢粉记录的环境演变

根据对巢湖490cm湖泊沉积物柱样7个AMS¹⁴C年龄的测定以及98个孢粉样品的分析,植物种类分属于86个（科）属,可以划分为6个孢粉组合带:孢粉带Ⅰ（9870～6040cal.aB.P.）代表了末次冰期之后全新世温暖气候到来之前气候转暖的早全新世过渡时期,气候呈现温和略干的特点,其中亚带Ⅰ-1（9870～7700cal.aB.P.）,Ⅰ-2（7700～6250cal.aB.P.）和Ⅰ-3（6250～6040cal.aB.P.）分别对应温暖湿润→温暖较湿→温和干燥的气候波动;孢粉带Ⅱ（6040～4860cal.aB.P.）代表中全新世温暖湿润期,水热配置条件最佳;孢粉带Ⅲ（4860～2170cal.aB.P.）体现中全新世后期温和干燥的气候,约2170cal.aB.P.干旱程度达到最高;孢粉带Ⅳ（2170～1040cal.aB.P.）反映巢湖流域由干燥向湿润气候的转型,气候总体上温和湿润;孢粉带Ⅴ（1040～200cal.aB.P.）反映了晚全新世巢湖流域温凉稍湿的气候;孢粉带Ⅵ（200cal.aB.P.至今）则体现巢湖流域处在相对温暖湿润的时期。植被类型演替大体为:以壳斗科的落叶、常绿属种为主的落叶阔叶、常绿阔叶混交林→以落叶栎类、栗属、青冈属和栲/石栎属为主的落叶阔叶、常绿阔叶混交林→以落叶栎类占绝对优势的落叶阔叶、常绿阔叶混交林→以禾本科为主的草地→以禾本科、蒿属和蓼属等为主的草丛。

POLLEN RECORD FROM CHAOHU LAKE IN THE LOWER REACHES OF THE CHANGJIANG RIVER AND ENVIRONMENTAL CHANGES SINCE 9870cal.aB.P.

A continuous typical lake sediment core with depths of 490cm was obtained from the Chaohu Lake(31°33'44.6″N,117°23'39.4″E)in the lower reaches of the Changjiang River,Anhui Province,China.7 dating data by AMS ¹⁴C method provide a high-resolution time scale and indicate that the core was deposited during the past 9870 years.86 pollen types were identified from 98 samples taken at 5cm intervals,among which arbors and shrubs are dominant.6 pollen zones were derived from bottom to top.In Zone Ⅰ,from 490cm to 337cm(9870-6040cal.aB.P.),the dominant pollen was arbors,pollen concentration was high,percentage of Quercus was high,and evergreen broad-leaf trees were less than deciduous broad-leaf trees,showing a relatively warm and dry climate after late-glacial period.According to pollen percentage spectrum and concentration spectrum,warm and humid→warm and moderately humid→warm and dry climatic fluctuations existed.In Zone Ⅱ,from 337cm to 247cm(6040-4860cal.aB.P.),pollen percentage of Moraceae was high,but there was a marked decrease in Castanopsis/Lithocarpus and a fast increase of Cyclobalanopsis,representing the Holocene Optimum and showing the best condition of water and heat with a warm and humid climate condition.In Zone Ⅲ,from 247cm to 117cm(4860-2170cal.aB.P.),pollen percentage of arbors researched the maximum value and concentrations of Cyclobalanopsis and Quercus(evergreen)were high,impling a warm-dry climate during the Holocene.Two obvious dry events occurred in 3760cal.aB.P.and 2170cal.aB.P.Zone Ⅳ,from 117cm to 87cm(2170-1040cal.aB.P.),pollen concentration increased but fluctuated greatly and Gramineae was the main component,representing a climatic transition period with relatively warm-wet climate in this area.In Zone Ⅴ,from 87cm to 17cm(1040-200cal.aB.P.),percentage of terraneous herbs and ferns was high and Pinus and trilete spore increased obviously,impling a relatively cool and wet climate during Late Holocene.In Zone Ⅵ,from 17-0cm(200-0cal.aB.P.),grassland occupied most areas around the lake with some conifers and broad-leaf trees,indicating that the climate during this period is relatively warm and moist with some cool-dry fluctuations.Five stages about the evolution of vegetation were reconstructed in this area as follows:(1)mixed forest of evergreen broad-leaf trees and deciduous broad-leaf trees with predominant Fagaceae;(2)mixed forest of evergreen broad-leaf trees and deciduous broad-leaf trees with predominant Quercus,Castanea,Cyclobalanopsis,and Castanopsis/Lithocarpus;(3)mixed forest of evergreen broad-leaf trees and deciduous broad-leaf trees with predominant Quercus;(4)grassland with predominant Gramineae;(5)grassland with predominant Gramineae,Artemisia,and Polygonum.The results correlate well with the previous researches around the research area.The climate reflected by pollen record fluctuates significantly in the Chaohu Lake during the Holocene.Palynological data from the Chaohu Lake gives new evidence for paleoenvironmental reconstruction of the lower reaches of the Changjiang River during the past 9870 years.The current primary research results show that the climate changes of this region not only are synchronous in a certain extent with other places,but also show local and regional characteristics.