DIATOM ASSEMBLAGES AND PALEOENVIRONMENTAL CHANGE OF THE HONGSHUIPAO PEATLAND IN THE MIDDLE PART OF THE GREAT KHINGAN MOUNTAINS SINCE THE MIDDLE HOLOCENE
本文提取大兴安岭中段红水泡泥炭地中晚全新世以来泥炭沉积中所含的硅藻化石,在82个样品中共发现32属94种硅藻。结合硅藻化石中优势种类生态特征,通过主成分分析发现,水位为控制该区域硅藻组合变化的最主要因素。其中,Meridion circulare,Meridion criculare var.constrictum等硅藻百分含量的升高指示水位的上升,Hantzschia amphioxys,Pinnulariaspp.等硅藻百分含量的升高伴随水位的下降。根据主成分得分建立的红水泡泥炭地古水位曲线发现,中晚全新世以来当地气候经历了数次干湿交替变化,在总体上趋于干旱。其中5000-3300 cal a BP为相对湿润期,优势种类为M.circulare,M.criculare var.constrictum;3300-1900 cal a BP为气候转干期,H.amphioxys,C.meneghiniana,Pinnulariaspp.成为该带中的优势种类;1900-600 cal a BP,该段内红水泡泥炭地水位较上一阶段进一步下降,气候继续转干;600-200 cal a BP为气候转湿期,红水泡泥炭地水位迅速上升,Achnanthes lanceolata含量迅速增加成为该段优势种;200 cal a BP至今,红水泡泥炭地水位迅速下降,Pinnulariaspp.成为该带中的绝对优势种。通过与季风区边缘其他研究区的古气候变化特征对比发现,红水泡泥炭地气候变化与多数研究区气候变化特征具有良好的一致性,因而推断其主要受东亚季风活动控制,泥炭沉积中硅藻化石组合记录可作为反映东亚季风变迁历史的良好指标。
英文摘要:
We extracted fossil diatoms from the Hongshuipao peatland in the middle part of the Great Khingan Mountains to study the climate change since the middle Holocene.A total of 94 taxa belonging to 32 genera were found in 82 samples.The result of Principal components analysis(PCA)method suggests that the water level would be the major driver for changes in fossil diatoms in the Hongshuipao peatland.An increase in species such as Meridion circulare,Meridion criculare var.constrictumindicates a wet condition;on the contrary,species such as Hantzschia amphioxys and Pinnulariaspp.become more abundant during the dry phases.The middle and late Holocene water levels are reconstructed based on sample scores on PCA axis 1.The result showed that the water level of the Hongshuipao peatland experienced several dry and wet changes and finally became shallower.The peatland water level was relatively high from 5.0 to 3.3 ka cal BP,and deep water species,such as M.circulare and M.criculare var.constrictum were dominant at that time,but it also noted a sudden drop of from 4.4 to 4.2 ka cal BP.Then the water level declined from 3.3 to 1.9 ka cal BP,shallower water species,such as H.amphioxys,C.meneghinianaand Pinnulariaspp.dominant at that time.The water level subsequently declined from 1.9 to 0.6 ka cal BP and increased markedly from 0.6 to 0.2 ka cal BP,when A.lanceolata became the dominant species.From 0.2 ka cal BP to the present,dominanted by Pinnularia spp.,the water level of the peatland became shallower again.The results obtained from fossil diatoms records are largely consistent with other palaeoenvironmental records in the edge of East Asian monsoon area,which implies the regional climate change was dominated by the East Asian monsoon since the middle Holocene.The palaeoenvironmental evolution indicated by fossil diatoms in Core HSP-2 can be used as a good clue to track the variability of the East Asian monsoon.