Department of Earth Sciences

Description

Stable hydrogen and oxygen isotopes in water vapor (δDv, δ¹⁸Ov) and precipitation (δDp, δ¹⁸Op) are widely used as tracers to improve our understanding of the hydrologic cycle on various time scales, from hourly variations to changes over millions of years (Botsyun et al., 2019; Pfahl and Wernli, 2008). Isotope fractionation is strongly dependent on temperature (Gat, 1996). Moreover, global atmospheric dynamics affecting stable water isotopes (Botsyun et al., 2016) is largely controlled by surface temperature. In this study, we aim to isolate the effects of sea surface temperature (SST) change (both increase and decrease) on stable water isotopes. Preliminary results show that the magnitude of isotopic change for the case of a 5°C decreased SST is > 8‰ and is most pronounced over continents, particularly over mountainous regions (Figure 1).

Approach

In this work, we will first analyze the completed model simulations. Two sensitivity experiments are performed with a high-resolution (∼0.75°) isotope-enabled general circulation model (ECHAM5-wiso). In these simulations, the SST is changed (increased and decreased) by 5°C. All other boundary conditions are kept as pre-industrial (year 1850). In the first step, student will be asked to analyze the global climate and associated isotope changes caused by the shift in SST. In the second step (or at M. Sc. level), additional ECHAM5-wiso experiments will be designed to test the impact of model resolution on the SST-isotope link.

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/improved 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.

Gat, J. R.: Oxygen and hydrogen isotopes in the hydrologic cycle, Annu. Rev. Earth Planet. Sci., 24(1), 225–262, 1996.

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.