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Lanzhou University (2021)

Pollen Recorded Humidity Changes in the Northern Margin of the Qinghai-tibetan Plateau over the past 300 Years and Comparison with Tree-ring Records

王嘉乐

Titre : Pollen Recorded Humidity Changes in the Northern Margin of the Qinghai-tibetan Plateau over the past 300 Years and Comparison with Tree-ring Records

Auteur : 王嘉乐

Grade : Master 2021

Université : Lanzhou University

Résumé partiel
The Qinghai-Tibetan Plateau(QTP)is a droven force and an amplifier of global climate change.The northern part of QTP is climatically influenced by the westerlies and the summer monsoon systems in the western and eastern part of Qilian Mountains respectively,and regional climate change has unique complexities of the transition zone between the two climate systems.Therefore,it is an ideal area for studying the interaction between monsoon and westerlies.With global warming,the spatial heterogeneity of humidity changes is strengthened.The past 300 years is a critical interval bridging the gap between meteorological records and geological records,and it also includes the transition period from the cold Little Ice Age(LIA)to the Current Warming Period(CWP).Here we use pollen record from core TE18A of Tian’E Lake(66 cm,128 samples in total with an average temporal resolution of~2 years)and core GH17B of Gahai Lake(42 cm,42 samples in total with an average temporal resolution of~8.5 years),with chronologies based on 210Pb and 137Cs,and compared with other climate records,mainly tree ring records,to discuss the spatial differences of humidity changes over the past 300 years.In the extremely arid area of the western Qilian Mountains and the surrounding dryland areas,where forest is absent,it is unclear how humidity conditions have changed over the past several centuries.We have obtained a high-resolution pollen record spanning the last 300 years from the sediments of Tian’E Lake in the western Qilian Mountains,which helps fill the spatial gap in recent climate records from the region.The results show that the pollen assemblages are dominated by Artemisia and Amaranthaceae(=Chenopodiaceae),and therefore the A/C ratio(Artemisia/Chenopodiaceae)can be used to reconstruct changes in humidity conditions.Based on the pollen A/C ratio,we found two relatively wet periods of~1740-1750 and 1840-1980,and two dry intervals of~1750-1840 and 1980-2018.This pattern of variation is similar to that reconstructed from nearby humidity records based on tree-ring width adjacent to Tian’E Lake area and with instrumental records from meteorological stations over the past several decades.However,forested mountain areas reflect local climate and may experience a different pattern of humidity variations than extensive dryland areas on a longer timescale.

Mots clés : northern Qinghai-Tibetan Plateau ;Qilian Mountains ;Tian’E Lake ;Gahai Lake ;pollen;global warming ;humidity changes ;

Présentation (CNKI)

Page publiée le 12 mars 2022