The Climate Change Of The Southern Tibetan Plateau During The Early-middle Holocene:Records Of Stable Carbon And Oxygen Isotopic Compositions Of The Mozhugongka Travertine,NE Lhasa

Global warming has caused great concern of geologists?especially paleoclimatologists?.Travertine as an important carrier of the paleoclimate environment,has important implications to understand regional and even global climate change.This paper makes a preliminary analysis regarding the petrology and stable carbon and oxygen isotopic compositions of the Mozhugongka travertine,Northeast Lhasa.The results showed that the ²³⁰Th age of the travertine ranges from11644±294 a BP to 7188±163 a BP,belongs to the Early-Middle Holocene.the time at the bottom of the travertine may extend to the late Pleistocene.Scanning electron microscope and energy spectrum analysis show that the travertine is mainly of inorganic origin with a trivial biological contribution.The travertine components are mainly calcite,followed by aragonite,undergoing moderate alteration of diagenetic.The carbon and oxygen isotope data reveals that the CO₂ source of the travertine is mainly caused by deep geothermal.In addition,the Mozhugongka travertine show bright laminaes alternating with dark laminaes.Compared to light laminaes,the dark laminaes are thinner and have lower values of?¹³C and?¹⁸O,these characteristics indicate that the dark layers formed in the summer-autumn season,but the light layers formed in the winter-Spring season.Finally,based on carbon and oxygen isotopic variations of the travertine,the climate change during the early-middle Holocene in Mozhugongka area is divided into three stages.Firstly,a warm and humid climate from 11.826 ka BP to 9.419 ka BP was related to a strong summer monsoon,however,a cold-dry event around 11.207 ka BP may be related to Younger Dryas.Thereafter,there is a climate turbulence period from 11.826 ka BP to 9.419 ka BP,composed of three warm-wet and cold-dry climate cycles.During this period,Three peaks of dry-cold climate were recorded at 9.381 ka BP,8.921 ka BP and 8.590 ka BP,these dry-cold events reflected the instability of the early Holocene climate and were global.Finally,from 8.254 ka BP to 7.150 ka BP,the climate is generally dry-cold,indicating that the Indian summer monsoon was in a stable recession.