Implications for soil environment from uranium isotopes of stalagmites

Abstract

By analyzing U and Th isotopic compositions of 41 samples in two stalagmites from Hulu Cave, Nanjing, we first discovered that variations of 23SV and a 23 'U o along the stalagmite growth-sequence (covering a period from 75 to 18 kaBP) are in high similarity to summer insolation curve at 33°N and a 18 0-based climate record of the studied stalagmites. The concentration of 238U is mainly controlled by content of organic matter in the soil above the cave. This mechanism can be used to explain our result that 238U curve of stalagmites is in phase with fluctuation of the a 18 0 record of the same stalagmites and summer insolation at cave locality. However, 238U concentration curve v.5. age is, in amplitude, inconsistent with the climatic curves, possibly due to complex processes of soil-water-rock interaction. a 234 u o indicates pedogenic intensity of soil profile above the cave and sensitively reflects alternations of pedogenesis and aeolian accumulation processes of Xiashu loess in Nanjing. Consequently, uranium concentration and its isotope ratio in stalagmites may provide a new proxy for climate change.

Speleothem Mg, Sr and Ba records during the MIS 5c-d, and implications for paleoclimate change in NE Sichuan, Central China

“…However, most of these reconstructions have focused solely on speleothem oxygen isotope ( 18 O) records, and much less attention has been paid to other proxies, including geochemical ones [4][5][6][7][8][9][10][11]. In particular, trace metals, such as Mg, Sr and Ba, which are common in speleothems, are seldom explored [4,7,8,11].…”

“…One of the most important issues for understanding climate change is to investigate variations of past climate and environment on various time scales, and to investigate their controlling mechanisms. In the past several decades, speleothems have been increasingly used for reconstruction of past climate and environments, and for the investigation of characteristics and controlling mechanisms of paleoclimatic and paleoenvironmental change [1][2][3][4][5]. In the East Asian summer monsoon (EASM) regime, speleothem-based reconstructions of past climates and environments have led to significant advances.…”