Fachbereich Geowissenschaften

Description

Stable hydrogen and oxygen isotopes in water vapour and precipitation are widely used as tracers to improve our understanding of the hydrological cycle on a variety of time scales, from hourly variations to changes over millions of years (Botsyun et al., 2019; Pfahl and Wernli, 2008). Stable water isotope proxy data (e.g., lake carbonates in which paleoprecipiation isotope values are preserved) are commonly used for paleoclimate reconstructions. However, mountain uplift affects both the climate and the preserved isotope signal (Botsyun et al., 2016, 2019). Therefore, reconstructing the influence of mountain elevation on stable water isotopes is critical for proper interpretation of paleoclimate data. Interactions between mid-latitude westerlies and the Tian Shan Mountains significantly impact climate patterns in Asia today (Sha et al., 2018) and Tian Shan uplift is hypothesised to play an important role in driving Asian climate change since the last ~ 30 Ma (Wang et al., 2020). Presently, Central Asia receives recycled, enriched with heavy isotopes moisture that has been mainly transported across Eurasia by the westerlies (Caves et al., 2015), but for the time when the Tian Shan Mountains were lower, the isotopic signature across the region remains enigmatic. Our preliminary analysis shows that Tian Shan uplift impact westerly and monsoon circulation in the region that results in precipitation and precipitation δ¹⁸O changes (Fig. 1).

Approach

This work will focus on analysing completed model simulations rather than creating new model runs. We propose using a high-resolution (∼0.75°) isotope-enabled general circulation model (ECHAM5-wiso). Experiments are conducted with boundary conditions for the pre-industrial (year 1850) and varied elevation of Tian Shan. Student will be asked to analyse climatological mid-latitude circulation change and associated surface hydroclimate change. For the M.Sc. – Lagrangian analysis tool “LAGRANTO'' (Sprenger and Wernli, 2015) will be applies to trace moisture trajectories changes for various Tian Shan elevation scenarios.

Requirements

Requirements for this project are an interest in stable water isotopes and paleoclimate, and a willingness to communicate in English (one of the supervisors is not a German speaker). Nevertheless, the final report can be written in German. Experience with scripting languages (Python, Ferret) would be helpful, but can be acquired during the project.

References

• Botsyun, S., Sepulchre, P., Risi, C. and Donnadieu, Y.: Impacts of Tibetan Plateau uplift on atmospheric dynamics and associated precipitation δ18O, Clim. Past, 12(6), 1401–1420, doi:10.5194/cp-12-1401-2016, 2016.
• Botsyun, S., Sepulchre, P., Donnadieu, Y., Risi, C., Licht, A. and Caves Rugenstein, J. K.: Revised paleoaltimetry data show low Tibetan Plateau elevation during the Eocene, Science (80-. )., 363(6430), eaaq1436, doi:10.1126/science.aaq1436, 2019.
• Caves, J. K., Winnick, M. J., Graham, S. A., Sjostrom, D. J., Mulch, A. and Chamberlain, C. P.: Role of the westerlies in Central Asia climate over the Cenozoic, Earth Planet. Sci. Lett., 428, 33–43, 2015.
• Pfahl, S. and Wernli, H.: Air parcel trajectory analysis of stable isotopes in water vapor in the eastern Mediterranean, J. Geophys. Res. Atmos., 113(20), 1–16, doi:10.1029/2008JD009839, 2008.
• Sha, Y., Shi, Z., Liu, X., An, Z., Li, X. and Chang, H.: Role of the Tian Shan Mountains and Pamir Plateau in increasing spatiotemporal differentiation of precipitation over interior Asia, J. Clim., 31(19), 8141–8162, 2018.
• Sprenger, M. and Wernli, H.: The LAGRANTO Lagrangian analysis tool–version 2.0, Geosci. Model Dev., 8(8), 2569–2586, 2015.
• Wang, X., Carrapa, B., Sun, Y., Dettman, D. L., Chapman, J. B., Caves Rugenstein, J. K., Clementz, M. T., DeCelles, P. G., Wang, M., Chen, J., Quade, J., Wang, F., Li, Z., Oimuhammadzoda, I., Gadoev, M., Lohmann, G., Zhang, X. and Chen, F.: The role of the westerlies and orography in Asian hydroclimate since the late Oligocene, Geology, 48(7), 728–732, doi:10.1130/G47400.1, 2020.