唐朝末年以来广西柳州干湿变化及人类活动演变

Climate and Human Disturbance Changes since the Late Tang Dynasty in the Karst Area of Liuzhou,Guangxi

中世纪暖期和小冰期是近2 000年气候变化中重要的气候事件,厘清其在低纬度地区干湿变化特征及其对古代农业发展及人口增长的影响,具有重要的意义。通过对广西柳州岩溶洞穴中一60 cm岩芯进行孢粉、炭屑分析发现,研究区的气候、稻作农业从唐末以来先后经历了6个阶段演化:1)875―940 a A.D.,C/P值及花粉记录指示:研究区气候整体偏干,水稻种植减少;2)940―1 050 a A.D.,C/P值及花粉记录指示:夏季风增强,水稻种植稍增长,人口增加;3)1 050―1 140 a A.D.,C/P值及花粉记录指示:夏季风减弱,稻作农业及人口较前期有所增长;4)1 140―1370 a A.D.,C/P值及莎草科花粉含量指示:研究区当时气候处于"中世纪暖期"温暖湿润期,稻作农业面积扩大,人口增加;5)1 370―1 900 a A.D.,C/P值及莎草科花粉含量指示:"小冰期"气候变干,水稻种植及人口逐渐减少;6)1 900―2 009 a A.D.气候变暖湿,水稻种植扩大,人口迅速增长。进一步对研究区气候事件与稻作农业及人口关系研究发现:历史时期气候事件与水稻种植、人口具有耦合关系,即中世纪暖期,气候暖湿,水稻种植扩大,人口增殖;小冰期,气候冷干,水稻种植萎缩,人口锐减。在非原地沉积时,莎草科和C/P对水分反映敏感,可以用来指示气候干湿变化。

Medieval Warm Period and Little Ice Age are important climatic events in the last two millenniums.To clarify the characteristics of dry and wet changes in low latitudes and its influence on the development of ancient agriculture and population growth is of great significance.A 60cm continuous cave-sedimental core from Liuzhou,Guangxi province,Southwest China,based on palynological investigation,has revealed that since the 875a A.D.,climate and human activities of the research area has undergone six stages:875a A.D.-940a A.D.,the pollen and C/P index both indicated drought event,meanwhile the rice cultivation gradually dropped.The population of the research region was poorly recorded after Late Tang Dynasty.940a A.D.-1050a A.D.,with the climate gradually transferring to humid,the rice cultivation generally developed,and so did the population.1050a A.D.-1140a A.D.,the C/P index pollen record and the stalagmiteδ^18O all referred this stage as a relatively dry climate,while the rice cultivation and population was similar with prior stage.1140a A.D.-1370a A.D.,Medieval Warm Period,the C/P and Cyperaceae pollen percentage was high,and the high rice pollen and low arboreal pollen also revealed strengthened human disturbance.The historical record indicated that the population of the research area grew quickly in this period.1370a A.D.-1900a A.D.,Little Ice Age,the climate was drying and cooling,indicated by pollen analysis,which affected the rice cultivation,and the population reduced continuously.1900a A.D.-2009a A.D.the climate recovered and the rice cultivation area expanded.The result also shows that the climate extremes have a strong corresponds with rice-cultivating and population:during Medieval Warm Period,climate was warm and humid which contributed to the growth of rice-cultivating and population,while in LIA,cold and dry climate decreased the population and the area of rice cultivation.When the Cyperaceae pollen is not local deposit,Cyperaceae pollen percentage and C/P,which are sensitive to moisture,can be used to indicate dry and wet climate changes.