High-resolution geochemistry records of climate changes since late-glacial from Dajiuhu peat in Shennongjia Mountains,Central China

A peat core with depths of 297 cm was obtained from the Dajiuhu Basin(31°29′27″N,109°59′45″E,1760 m)in Hubei Province,Central China.10 AMS ages provide a time control and reveal that this core spans the past about 16.0 kaBP(calibrated age)(1 4C age:13.3 kaBP).Multi-proxy indexes analysis of geochemistry shows the following character of climate and environmental changes since about 16 kaBP:(1) The climate during the late-glacial period was cold and wet as a whole,but fluctuated continually.11.4- 12.6 cal.kaBP,12.6-15.2 cal.kaBP and 15.2-16 kaBP were corresponding respectively to the Younger Drays,Bφlling-Allerφd Warm Period and the Oldest Drays.(2)Inheriting the some climate characteristics of the late-glacial,the climate during the early-Holocene was wet and temperature increased gradually,during which an obvious dry event around 10.6 cal.kaB appeared.(3)The climate during the mid-Holocene was genarally warm and wet.During 9.2-7.5 kaBP,temperature increased gradually, precipitation was less comparatively and the 8.2 kaBP cold event which might be representative in the globe was reflected markedly.Then,multi-proxy records were relatively stable during 6.7-4.2 kaBP, which shows the best water and thermal condition in the Holocene Optimum.(4)Around 4.2 kaBP,the climate and environment transform from warm and wet to cool and dry,which may result in the collapse of the Neolithic Culture and midwifery the civilization of Xia Dynasty in this region.After 0.9 kaBP,the climate turned cool and wet.Climate and environmental changes archived in Dajiuhu peat respond to the global changes since the late-glacial period and can be contrasted to the changes recorded in other high-resolution archives from the East Asia Monsoon region,which take on the variety model that the monsoon strengthened abruptly after the late-glacial,was strong during the early Holocene,subse- quently declined and became weak after the middle Holocene with dry climate.According to our analysis,the driving mechanism should be the response of s     

Sensitivity of pollen factors in the climate transfer function

Constructing a mathematic transfer function of pollen and climatic factors is one of the most important approaches in the quantitative reconstruction of paleoclimate elements.In the function building,the key point is the response sensitivity to the climate change for different pollen families and categories. As an example in this paper,the pollen samples from the surface and stratum in Dajiuhu basin,Shennongjia are used to estimate the sensitivity of pollen factor-temperature in the transfer function by the EOF analysis,multiple regression and stepwise regression techniques.Thereafter,the selection methods of pollen factors are discussed and compared with other results from different researchers. The results show that in the pollen samples,the quantity of woody plants is larger than others,but the woody plants have relatively lower sensitivity and slow responses to the climate evolution and abrupt climate change.While the pollens from lower grade plants(herb and fern)have a relatively high sensi- tivity to the temperature change and fast response to the abrupt climate changes.Therefore,the pollen of herb and fern may significantly record the extreme events in the climate change.Also in different regions,the pollen samples have different sensitivity and optimum combination in the transfer functions.Final conclusion is that the stepwise regression is one of the best methods for transfer function building since it can obtain the maximum multiple correlation coefficients and optimum combination of sensitive pollen factors.     

Spore-pollen-climate factor transfer function and paleoenvironment reconstruction in Dajiuhu, Shennongjia,Central China

The identified results of 121 surface sediment spore-pollen samples in Shennongjia and meteorological data base of 30 years(January,1971―December,2000)of 7 meteorological stations around Dajiuhu, Shennongjia are used in this study.Selecting 55 species of common spore-pollen with the method of space fitting and stepwise regression we construct the pollen climate factor transfer function of annual mean tem- perature:T=7.649-2.33097X Abies -0.10873X Betula -0.17352X Compositae -0.13176X Cruciferae +0.13356XEuphorbiaceae -0.83069X Campanulaceae +1.96494XPyrrosia+0.38411XPteris+2.77741XSelaginella+0.04439XMonolites.We had reconstructed annual mean temperature series by use of the sporo-pollen samples concentra-tion percentage in peat section with 297 cm thickness in Dajiuhu since 15.753 kaBP.The temperature series reflect well the character of climatic change since the late glacial,which indicates extreme cold climate event of the Oldest Dryas,the Older Dryas,the Younger Dryas and the 8.2 kaBP,the same to the climate fluctuations of Bolling Warm Period and Allerod Warm Period,and the character of temperature change fluctuating frequently at the transition age from the late glacial to the Holocene.The reconstructed temperature also indicate Holocene Optimum,late Holocene warm-dry climate,and the character of climatic change in Dajiuhu in the last 1 ka.The conclusion is that the sporo-pollen samples have important climatic significance to surface sediment and the section of Dajiuhu,Shennongjia and important reference value to studying climatic change during the last glaciation by the temperature transfer function and reconstructed temperature series.     

神农架大九湖泥炭藓Sphagnum palustre沼泽特征分析

在实地调查的基础上 ,本文对神农架大九湖泥炭藓沼泽的植被组成 ,群落学特征 ,发育趋势作了详细的阐述     

不同沼泽地对神农架大九湖湿地土壤—植被碳氮磷化学计量比的影响

湿地生态系统碳氮磷(C、N、P)生态化学计量比已成为当前探索群落生态动态过程的热点.然而,人类活动对沼泽湿地生态化学计量比的影响规律及其影响机制尚未明确.以神农架大九湖沼泽湿地为研究对象,探索植被—土壤碳氮磷生态化学计量比及其对人类活动的响应规律,以期为该区域湿地保护恢复提供决策支撑.研究表明:随着人类活动的影响,与泥...