Seasonal temperature changes obtained from carbonate clumped isotopes of annually laminated tufas from Japan: Discrepancy between natural and synthetic calcites

Hirokazu Kato, Shota Amekawa, Akihiro Kano, Taiki Mori, Yoshihiro Kuwahara, Jay Quade

研究成果: Contribution to journalArticle査読

8 被引用数 (Scopus)

抄録

Carbonate clumped isotopes provide a novel paleo-thermometer that does not require knowledge of the isotopic compositions of environmental water. Despite considerable effort, there are substantial inter-laboratory disagreements in empirical calibrations between the abundance anomaly of the clumped isotopes (Δ47) and absolute temperature, and discrepancies in paleo-temperature estimates from natural samples. In this study, clumped isotopes using two types of 17O corrections were analyzed for two sample sets of synthetic calcites and tufas collected monthly from two sites in southwest Japan with known δ18O values and temperatures of parent water. These measurements form the basis for two new temperature calibrations of carbonate clumped isotopes, the first from our Kyushu University laboratory in Japan. The calcites synthesized at four different temperatures (2.9–61.0 °C) yield a temperature-Δ47 relationship of Δ47=0.0354±0.0013×106/T2+0.290±0.015 (R2 = 0.986), which is indistinguishable from the calibrations of other recent studies based on acid digestion experiments at high temperature (70–100 °C). The Δ47 thermometry for the natural tufa samples display the seasonal pattern of water temperature better than the δ18O thermometry. However, the Δ47 values of the tufa samples deposited at temperatures ranging from 5.6 to 16.0 °C were lower than the values expected from the calibration using synthetic calcites, thus providing another temperature calibration of Δ47=0.0336±0.0036×106/T2+0.301±0.048 (R2 = 0.735). Therefore, our results clearly identify a detectable, but fairly uniform, discrepancy in Δ47-temperature calibration between synthetic calcite and natural samples (tufas). The amplitude of Δ47 offset between the tufa and synthetic samples appears to be independent of the seasonal change in water temperature and the chemical properties of water, including pH, pCO2, and precipitation rate of calcite. The lower Δ47 values have been previously reported from other tufas and travertines, and therefore appear to be associated with processes inherent to tufas and travertines, such as CO2 degassing. We also find that our results are insignificantly influenced by types of 17O corrections and almost independent with bulk isotopic composition.

本文言語英語
ページ(範囲)548-564
ページ数17
ジャーナルGeochimica et Cosmochimica Acta
244
DOI
出版ステータス出版済み - 1 1 2019
外部発表はい

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

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