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Advance in study of oxygen and carbon isotope variations in cave stalagmites as Palaeo-climate proxies

KONG Xing-gong   

  1. College of Geography Science, Nanjing Normal University, Nanjing 210046, China
  • Received:2009-06-20 Revised:2009-06-20 Online:2009-06-20 Published:2009-06-20

Abstract: Stalagmites are now regarded as valuable archives in study of climatic conditions on the continents. They are ideal materials for precise U-series dating, yielding ages in calendar years, coupled with annual layer counting, the chronology of stable oxygen-isotope then be made with the resolution higher than year. These absolute precise dating and high resolution records offer a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores. In many cases, stalagmite records may provide climate conditions that rival those obtained from marine sediments and ice cores. The controls on stalagmite δ18O are numerous, under equilibrium condition, the δ18O values of stalagmites are related to intensity of summer monsoon or amount of the monsoon precipitation at the typical monsoon area. This emphasis on global climate teleconnections has replaced attempts to constrain absolute palaeotemperature, allowing the scientific community to place global climate changes on a firm chronological and climate dynamical footing. Unlike the global comparison of δ18O, under equilibrium open system conditions, the δ13C of the dissolved species reflects the isotopic composition of the soil CO2, with no detectable isotopic imprint from the carbonate host-rock. Thus the stalagmite δ13C is mainly controlled by the vegetation covering the cave, normally by the C3/C4 ratio of the local vegetation. The δ13C can still be related to the change of precipitation and temperature at special region.We should pay special attention to these processes including evaporation, rapid degassing of cave dripwaters, kinetic fractionation,CO2 degassing of dripwaters and consequent calcite precipitation in the vadose zone above a cave that could affect the carbonisotope to a relatively heavier signature. The literature is reviewed briefly to provide for the readers a sense of the current research work of the stable isotope of stalagmite and provide some ideas for future research directions.