VARIATION IN URANIUM ISOTOPES OF STALAGMITES FROM SANBAO CAVE, HUBEI PROVINCE: IMPLICATIONS FOR PALAEOCLIMATE: VARIATION IN URANIUM ISOTOPES OF STALAGMITES FROM SANBAO CAVE, HUBEI PROVINCE: IMPLICATIONS FOR PALAEOCLIMATE

A great number of oxygen isotope ratios and U-Th ages data were collected and studied by the authors for the stalagmites from the Sanbao cave,Hubei Province,China.Uranium-series dating of the speleothem suggests that the stalagmites are formed in the period from the penultimate glacial period up to the present.This paper deals with the relationship between uranium concentration in stalagmites and paleoclimate data induced from the 160 precise ICP-MS 230Th data collected from 17 stalagmites from the Sanbao Cave.We discovered that the variations in 238U show a negative relation with the δ18O records of the studied stalagmites,and a positive relation with the temperature changes in West Pacific Warm Pool.The concentration of 238U in the stalagmites fluctuated rapidly during the interglacial periods,slowly during the glacial periods,and increased sharply in the past two terminations.On the orbital scale,the higher the average growth rate,the higher the uranium concentration is,and vice versa.The results also show that the pedogenic processes of the soil profile above the cave and the complex soil-water-rock interaction are well related with the outer-cave climate changes,possibly responsible for the shifts of uranium concentration.However,the shift of the 234U/238U in stalagmites seems having no any relation with the external palaeoenvironment over the past 180000 years.Therefore,the uranium concentration in the stalagmite could only be used as a new proxy for climate change with caution.