Vegetation And Climate Change Recorded By Pollen In Gahai Lake During The Past 500 Years

The climate change of the past millennium is a key stage to connect modern instrumental data with past climate proxy indicators.Strengthening high-resolution climate research on the millennium scale will help us deepen our understanding of today's climate issues,and improve our ability to predict future climate changes on a short-term scale and to respond to climate abrupt changes.Based on the changes in pollen and grain size and other climatic proxy indicators of borehole GH19-10 in the northeast of the Qinghai-Tibet Plateau,this paper discusses the vegetation and climate evolution history of the Gahai area in the past 500 years,and compares with existing research to analyze the changes.The climate evolution of Gahai,retrieved by pollen,grain size and other climate proxy data,can be divided into three stages:Stage ?(1533-1720 AD):Regional wind activities are frequent,climate fluctuations are large,regional effective humidity is high,and the overall climate is cold and wet.1533-1575 AD,low pollen concentration,poor vegetation coverage,low pollen A/C value,and low regional effective humidity.The particle size is generally small,the lake's hydrodynamic force is weak,and the climate is relatively dry.1575-1720 AD,corresponding to the ice peak of the Little Ice Age.The particle size components are generally coarser,the wind and sand activities are intense,the winter monsoon is relatively strong,and the climate is relatively cold.In the pollen assemblage,the humidity-loving Artemisia pollen content increases,the A/C value is high,the regional effective humidity is high,and the climate is cold and wet.Phase ?(1720-1900 AD):Regional wind activity weakens,climate fluctuations slow down,regional effective humidity decreases,and the climate is drier.1720-1848 AD,the overall particle size becomes finer,the components of the wind-sand sand decreases,and the wind-sand activity weakens.In the sporopollen assemblage,the dry-like Chenopodiaceae pollen content increased,the A/C value was low,the regional effective humidity was low,the pollen concentration also showed a low value,and the vegetation coverage was poor;1848-1900 AD,the regional effective humidity increased,and drought Remission,the end of the Little Ice Age.In the third stage(1900-2016 AD):regional aridification has intensified,and human activities have an impact on regional environmental changes.From 1900-1977 AD,the particle size became coarser,the components of the wind-blown sand increased,and the wind-blown sand activity intensified.Corresponding to modern sand and dust weather,the pollen A/C value decreased,the regional effective humidity became lower,and the regional climate was relatively dry;From 1977 to 2016 AD,the content of Nitraria and Gramineae in the pollen assemblage increased,the impact of human activities was intensified,and the significance of pollen indicators was weakened.The effective humidity in the area retrieved by the A/C value of borehole GH19-10 corresponds well to the dry and wet stages divided by Delingha tree rings and ice cores before 1950 AD,and Gahai humidity can respond well to regional precipitation The change.After 1950 AD,instrumental data showed that the precipitation in Delingha area increased,while the Gahai A/C value showed that the regional humidity was decreasing.This is because the effective humidity is affected by the combined effects of temperature and precipitation,and it is not completely equivalent to changes in precipitation.After 1990 AD,the effective humidity of Gahai increased and the effective humidity of Tosu Lake decreased,showing that the A/C value under the influence of strong human activities cannot well indicate regional humidity changes.The climate change in the Gahai area is mainly affected by factors such as solar radiation and sea-atmosphere interaction.