A novel application of triple oxygen isotope ratios of speleothems

Lijuan Sha, Sasadhar Mahata, Pengzhen Duan, Boaz Luz, Pu Zhang, Jonathan Baker, Baoyun Zong, Youfeng Ning, Yassine Ait Brahim, Haiwei Zhang, R. Lawrence Edwards, Hai Cheng

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

We present triple oxygen isotope data from speleothems obtained by an O2-CO2 Pt-catalyzed oxygen-isotope equilibration method. The high precision (9 per meg or better, 1σ SD) of our new speleothem Δ17O (carbonate 17O anomaly) data is sufficient to resolve subtle hydroclimatic signals. In addition, we determined triple oxygen isotope fractionation factors through two sets of modern paired carbonate-dripwater samples collected at a temperature of 17 ± 1 °C, which is prerequisite to the calculation of triple oxygen isotope compositions of parent meteoric waters at cave sites from speleothem proxy data. Based on this calibration, we back calculated triple oxygen isotope compositions of parent waters across well-characterized climate transitions using speleothem proxy data from three regions. Resulting oxygen-isotope data closely track the Global Meteoric Water Line (GMWL), providing a preliminary validation of the method. Our speleothem Δ17O data indicate a 21 per meg difference between Marine Isotope Stage 5d and 5e in samples from Central Asia and a 15 per meg difference between the Middle Holocene and Last Glacial Maximum in samples from the eastern Mediterranean, suggesting a shift in moisture source and/or fractionation history. Unexpectedly, there were no measurable Δ17O differences between glacial and interglacial samples from both the South American (western Amazon) and Asian (southern China) monsoon domains, implying consistent moisture-source conditions across glacial and interglacial cycles, at least in terms of relative humidity. Remarkably, Δ17O values from the western Amazonian samples are significantly higher (∼20 per meg) than those from Asian monsoon regions, suggesting lower relative humidity along moisture trajectories in the western Amazon during the Middle Holocene and Last Glacial period. Similarly, Δ17O values of the eastern Mediterranean samples are significantly higher (19–55 per meg) than those of coeval samples from Central Asia, implying different hydrological environments or moisture sources despite being in the same westerly circulation domain. Speleothem Δ17O data may thus provide new and important constraints for understanding regional and global hydroclimate dynamics.

Original languageEnglish (US)
Pages (from-to)360-378
Number of pages19
JournalGeochimica et Cosmochimica Acta
Volume270
DOIs
StatePublished - Feb 1 2020

Bibliographical note

Funding Information:
This work was supported by grants from National Natural Science Foundation of China, China (Nos. 41888101, 41561144003, 41761144069 and 41731174), Israel Scinece Foundation, Israel (Grant No. 633/15) and National Science Foundation, USA (Grant No. 1702816). Dr. E. Barkan is greatly appreciated for his mentoring in all laboratory aspects. We also thank M.C. Liang, H.P. Affek, and I. Musan for their continual helps to set up the method in Xi'an Jiaotong University. We are grateful to Prof. T.Y. Li and Mr. C.J. Chen, and J.J. Yin for providing the paired modern cave carbonates/dripwater samples. Finally, the authors appreciate the suggestions made by Associate Editor Jay Quade and two anonymous reviewers, which helped to improve the original manuscript.

Funding Information:
This work was supported by grants from National Natural Science Foundation of China , China (Nos. 41888101 , 41561144003 , 41761144069 and 41731174 ), Israel Scinece Foundation , Israel (Grant No. 633/15 ) and National Science Foundation , USA (Grant No. 1702816 ). Dr. E. Barkan is greatly appreciated for his mentoring in all laboratory aspects. We also thank M.C. Liang, H.P. Affek, and I. Musan for their continual helps to set up the method in Xi'an Jiaotong University. We are grateful to Prof. T.Y. Li and Mr. C.J. Chen, and J.J. Yin for providing the paired modern cave carbonates/dripwater samples. Finally, the authors appreciate the suggestions made by Associate Editor Jay Quade and two anonymous reviewers, which helped to improve the original manuscript. Appendix A

Keywords

  • Dripwater
  • Moisture source
  • Paleohydroclimate
  • Relative humidity
  • Speleothems
  • Triple oxygen isotope

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