3:30 PM - 3:45 PM
[MIS10-13] Seasonal temperature changes recorded in carbonate clumped isotopes of tufas
★Invited Papers
Keywords:carbonate, clumped isotopes, tufa, oxygen isotope
The carbonate clumped isotopes thermometry is a novel technique to reconstruct the temperature of mineral precipitation without the isotopic information of the parent water. The abundance anomaly of 47CO2 (Δ47) generated by acid digestion of calcite is an index of temperature (Ghosh et al. 2006). However, natural samples often show unexpected Δ47 values likely due to kinetic effect. We analyzed the clumped isotopes of two sample sets, synthetic calcites and natural tufa deposits. The calcites synthesized at four different temperatures (2.9–61.0°C) were in equilibrium for the oxygen isotopes. Tufa samples were collected from two sites, Shimokuraida (Okayama Pref.) and Shirokawa (Ehime Pref.), every month during a period from December 1998 to December 2000 (Kano et al., 2003; Kawai et al., 2006). Analyzed materials were carefully collected from the superficial 0.5 mm of each tufa sample which has a depositional interval of around 45 days.
Our Δ47-temperature calibration by the synthetic calcites is undistinguishable from many previous studies. A typical inter-measurement error was 0.0078‰ (1σ) estimated by in-house standard, which corresponds to 1.2°C in temperature.
The tufa Δ47 exhibited clear seasonal patterns ranged from 0.695‰ (Dec. 2000) to 0.731‰ (Aug. 2000) in Shimokuraida and from 0.696‰ (Jan. 2000) to 0.733‰ (Oct. 1999) in Shirokawa. These ranges correspond to 10.1–22.5°C and 9.7–22.3°C and these temperature ranges are 0–7°C higher than the actual water temperatures (ranging from 5.6 to 16.0ºC). The temperature offset at both sites became the largest in late summer and early autumn, when the water had high pCO2 and precipitation rate. It is assumed that active CO2 degassing and rapid calcite precipitation caused the temperature offset.
Although absolute temperature calibration of natural samples is in need of improvement, our tufa Δ47 values exhibited clearer seasonal patterns rather than in conventional δ18O thermometry.
Reference
1. Ghosh P., Adkins J., Affek H., Balta B., Guo W. F., Schauble E. A., Schrag D. and Eiler J. M. (2006) 13C–18O bonds in carbonate minerals: a new kind of paleothermometer. Geochim. Cosmochim. Acta 70, 1439–1456.
2. Kano A., Matsuoka J., Kojo T. and Fujii H. (2003) Origin of annual laminations in tufa deposits, southwest Japan. Palaeogeogr. Palaeoclimatol. Palaeoecol. 191, 243–262.
3. Kawai T., Kano A., Matsuoka J. and Ihara T. (2006) Seasonal variation in water chemistry and depositional processes in a tufa-bearing stream in SW-Japan, based on 5 years of monthly observations. Chem. Geol. 232, 33–53.
Our Δ47-temperature calibration by the synthetic calcites is undistinguishable from many previous studies. A typical inter-measurement error was 0.0078‰ (1σ) estimated by in-house standard, which corresponds to 1.2°C in temperature.
The tufa Δ47 exhibited clear seasonal patterns ranged from 0.695‰ (Dec. 2000) to 0.731‰ (Aug. 2000) in Shimokuraida and from 0.696‰ (Jan. 2000) to 0.733‰ (Oct. 1999) in Shirokawa. These ranges correspond to 10.1–22.5°C and 9.7–22.3°C and these temperature ranges are 0–7°C higher than the actual water temperatures (ranging from 5.6 to 16.0ºC). The temperature offset at both sites became the largest in late summer and early autumn, when the water had high pCO2 and precipitation rate. It is assumed that active CO2 degassing and rapid calcite precipitation caused the temperature offset.
Although absolute temperature calibration of natural samples is in need of improvement, our tufa Δ47 values exhibited clearer seasonal patterns rather than in conventional δ18O thermometry.
Reference
1. Ghosh P., Adkins J., Affek H., Balta B., Guo W. F., Schauble E. A., Schrag D. and Eiler J. M. (2006) 13C–18O bonds in carbonate minerals: a new kind of paleothermometer. Geochim. Cosmochim. Acta 70, 1439–1456.
2. Kano A., Matsuoka J., Kojo T. and Fujii H. (2003) Origin of annual laminations in tufa deposits, southwest Japan. Palaeogeogr. Palaeoclimatol. Palaeoecol. 191, 243–262.
3. Kawai T., Kano A., Matsuoka J. and Ihara T. (2006) Seasonal variation in water chemistry and depositional processes in a tufa-bearing stream in SW-Japan, based on 5 years of monthly observations. Chem. Geol. 232, 33–53.