Vegetation And Climate Changes Reflected By Palynology In Chongce Ice Core On Tibetan Plateau During 1820?1916 AD

As one of the most direct and reliable proxies,pollen and spores can be used to reflect the paleoenvironmental and paleoclimate changes at different time scales.Palynology in snow and ice provides a new version for climate reconstruction when taking both advantages of pollen and spores,as well as snow and ice.In foreign researches,regional studies have been carried out in Arctic areas,but it is limited by the low pollen concentration,low sampling resolution,and inadequate species identification.More in-depth researches on modern process have been developed in mountainous areas and great progress has been made in respect of pollen-based ice core dating in these areas.In domestic researches,the key content focus on the relationship between pollen records and climate changes in ice caps such as Dunde,Guliya and Puruogangri.In view of abundant paleoclimate records on TP(Tibetan Plateau),palynology in snow and ice can not only provide the information on vegetation succession,but also confirm with other paleoclimatic indicators,so it is of great significance for paleoclimate reconstruction.So far,there are few studies on TP concerning the palynology in ice cores and fewer pollen records in ice cores with high resolution,continuous and long time series.Based on the pollen identification results of upper 29.8-53.1 m from the 216.6 m Chongce ice core,the vegetation and climate change information was reconstructed for the period from 1820 to 1916.The conclusions are as follows:1)In this paper,more than 60 pollen taxa in Chongce Ice core were identified,including trees and shrubs such as Pinus,Betula,Alnus,Carpinus/Corylus,Abies,Quercus D,Juglans,Pterocarya,Rosaceae,Hippophae,Rhamnaceae,Nitraria,Ulmus;herbs such as Chenopodiaceae,Artemisia,Poaceae,Aster,Labiatae,Umbelliferae,Cruciferae,Humulus,Solanum,Ranunculaceae,Thalictrum;spores such as Triletes,Polypodiaceae,Gleicheniaceae.The taxa of pollen and spores identified by Chongce Ice Core is basically the same as the modern vegetation pollen types.Therefore,the pollen and spores of Chongce Ice Core can reflect the regional vegetation in Chongce area.2)The characteristics of pollen assemblage in Chongce ice core are as follows:arbor pollen is characterized by high percentage of Pinus,followed by Betulaceae;desert pollen is characterized by high percentage of Chenopodiaceae,only in a specific period of time can Ephedraceae reaches a high value;steppe pollen is characterized by high percentage of Artemisia and poaceae.The average percentage of Chenopodiaceae and Artemisia is 26.6%and 15%respectively.The sum of them is more than 50%in most periods,so it is concluded that these two are the most important pollen types in Chongce area.3)The vegetation changes in Chongce area during 1820-1916 AD were as follows:1820-1852 AD,the steppe vegetation successed to desert types;1852-1887 AD,the desert vegetation evolved to steppe types;1887-1916 AD,the vegetation evolution is still in progress from desert to steppe.4)The humidity changes in Chongce area during 1820-1916 AD were as follows:there are four humidity periods in Chongce area,1820-1825 AD,1843-1849 AD,18851895 AD and 1905-1916 AD.1820-1852 AD,the humidity changed from wet to dry;1852-1887 AD,the humidity gradually changed from dry to wet;1887-1916 AD,the humidity increased further.