THE CHARACTERISTICS OF CLIMATIC TRANSITION FROM ALLERØD TO EARLY YOUNGER DRYAS

Three U-Th dates, 336 pairs of δ¹⁸O data and 1440 laminar-thicknesses have been measured for QT17 stalagmite from Qingtian Cave in Shennongjia area, Hubei Province. An averaged 4-year-resolution absolute-dated oxygen isotope record from Qingtian Cave represents East Asian monsoon history during the period from 13.5 to 12.1 kaBP. This record bears a high similarity to a grey level record of varved sediments from Cariaco basin in terms of their fluctuation and amplitude at the transition during the period from Allerød to early Younger Dryas. On the contrary, both new Greenland ice cores (GISP2 and GRIP) δ¹⁸O records show large amplitude during that period. Within the dating error, the four records are approximately synchronous at millennical time scale, which supports the coupled link between northern high and low latitudes in climate systems. Despite of the four records in phase, these records display different durations for this transition. We can see from the records in Atlantic climate region(including the two Greenland ice cores)and Caricao basin that the transition lasts 230~400 years only. From the annual layer counting result, our monsoon record shows much longer duration, about 550 years. We interpret the long duration as a mixed isotope effect of the monsoon precipitation and its sourced sea water.