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Lanzhou University (2022)

Coupling Relationship between Climate and Ecological Environment in the Agro-pastoral Ecotone in Northern China Since Holocene

张丽

Titre : Coupling Relationship between Climate and Ecological Environment in the Agro-pastoral Ecotone in Northern China Since Holocene

Auteur : 张丽

Grade : Doctoral Dissertation 2022

Université : Lanzhou University

Résumé partiel
The uncertainty of the climate evolution since the last glaciation will have a great impact on the survival and development of mankind,especially the abnormal climate since the Holocene.The climate instability of the Holocene warns us that the future living environment of mankind is very uncertain.With the increasing impact of human activities on the natural environment and the increase of“greenhouse gas”emissions year by year,the impact of global temperature rise on the environment in the future is one of the hotspots of general concern.The argo-pastoral ecotone is the transition zone between agriculture to grassland animal husbandry ecosystem in China,and it serves as the East Asian monsoon transition belt.The change of precipitation patterns caused by the East Asian summer monsoon intensity was the primary factor limiting the scope of the agro-pastoral range.In addition,human factors affect the distribution pattern of the modern agro-pastoral ecotone,resulting in frequent swings of the agro-pastoral boundary.Two sections in the central part of the northern agro-pastoral ecotone were selected for the research.The first component is the fluvial-lacustrine-eolian deposit from Dishaogowan section in the Salawusu River valley,located in the desert-loess ecotone.The second section is the lacustrine-eolian deposit from Tengger Nuur lake,in the sandy-steppe transition area.Based on the analysis of palaeoclimate proxies such as end-member of grain size,δ13Corg,n-alkanes,TOC,C/N and Fe2+contents of sediments,the paleoenvironment of the northern agro-pastoral ecotone since Holocene was reconstructed.The evolution process and characteristics of the East Asian monsoon system and ecological environment were recognized,as was the interaction between wind-blown sand activities and climate,as well as the coupling relationship between climate and environment evolution since the Holocene was discussed.The main understanding of this paper is as follows:The end-member(EM)analysis of grain-size distribution in Dishaogouwan section yielded an optimal model with 3 EMs,EM1(30.2μm and 363.1μm)represents the aeolian sand,EM3(19.18μm and 195.1μm)represents aeolian sand from promixal or local-source and EM2(19.95μm and 120.2μm)belongs to the shore-shallow lacustrine sand component in lacustrine deposits.The sediment from Tengger Nuur lake is mainly composed of 4 EMs and gravel component as well.EM1(5.012μm)belongs to long-term suspended fine silt,reflecting the change of lake water level ;EM2(17.38μm)belongs to offshore suspended particles,representing long-distant transportation of aeolian sand ;EM3(104.7μm)belongs to nearshore suspended component of shore-shallow lacustrine facies,reflecting the change of runoff ;EM4(363.1μm)belongs to jumping particles of Nearshore zone,representing promixal or local-source sand,reflecting the strength of winter monsoon.

Mots clés : Holocene ;Dishaogouwan;Tengger Nuur ;agro-pastoral ecotone ;EASM;

Présentation (CNKI)

Page publiée le 15 octobre 2022