[MIS23-P08] Seasonal change recorded in carbonate clumped isotope of tufa deposits
Keywords:Clumped isotope, tufa, thermometer
The generated carbon dioxide was carefully purified in column cooled at -10ºC, and measured by MAT 253 with applying the background correction of He et al. (2012). Each value was adjusted on the absolute reference frame of Dennis et al. (2011). A typical measuring error was 0.015 permil (1s) that corresponds to 3ºC in the temperature range of Hiro-1. We applied the temperature equation based on our own measurements of synthesized calcites of known temperatures, which is very similar to the theoretical equation of Guo et al. (2009).
The fufas from Ehime Prefecture indicated a clear seasonal changes of temperature ranging from 3.7 to 20.9ºC, which is consistent with measured temperature range of 5-19ºC. A similar consistent result from the Okayama tufa indicates that the carbonate clumped isotope of tufa can be used for a thermometer. CO2 degassing was observed in these tufa sites, but did not resulted in a recognizable disequilibrium. We suspect that the kinetic effect was insignificant in a pH condition around 8.3 where the dominant carbonate species is bicarbonate.