The concept of stable isotopes

Stable water isotopes in atmospheric research
Stable water isotopes (oxygen 18 and deuterium) are an important observational tool for climate reconstructions from palaeoarchives, such as ice cores. Once callibrated with present-day temperatures, they can be used to reconstruct the temperature changes during the ice ages. These callibrations are possible because the concentration of stable isotopes in water vapour and precipitation depends on the meteorological conditions during the water’s transport history, in particular the temperatures during condensation.

While the climatic isotope information is widely used, it is not fully understood how for example seasonal or inter-annual variability of atmospheric circulation influence the isotope signal. This research focuses on the atmospheric conditions during isotope fractionation along its transport path, based on individual precipitation events. The aim is to gain a better physical understanding of the short-term isotope variability in palaeo archives, and use stable isotopes as an observational tool to validate the hydrological cycle in atmospheric models.

Figure 1: Sketch of stable isotopes fractionation processes during atmospheric transport. Point on the numbers to see a description of each process. From Sodemann (2006).

Inter-annual variability of stable water isotopes in Greenland
We investigated to what extent the inter-annual changes of stable isotopes in Greenland precipitation can be explained when the full moisture transport history is considered. To this end, we studied the transport of water to Greenland during winter months with different North Atlantic Oscillation (NAO) phases using a Lagrangian moisture diagnostic. The results show that modelled inter-annual variability is to 2/3 caused by the strong changes of atmospheric moisture transport to Greenland for different winters. One third is due to the fact that moisture from different evaporation sources is brought to Greenland. There remain however considerable uncertainties with respect to how stable water isotopes are brought into Lagrangian transport models.

Figure 2: Modelled isotopic composition (oxygen 18) of Greenland winter precipitation for the positive NAO phase (left), and the negative NAO phase (right).

Relevant publications

  • Sodemann, H., Schwierz, C., and Wernli, H., 2008: Inter-annual variability of Greenland winter precipitation sources. Lagrangian moisture diagnostic and North Atlantic Oscillation influence, J. Geophys. Res., 113, D03107, doi:10.1029/2007JD008503. [Abstract, PDF, 6.4MB]
  • Sodemann, H., Masson-Delmotte, V., Schwierz, C., Vinther, B. M. and Wernli, H., 2008: Inter-annual variability of Greenland winter precipitation sources. Part II: Effects of North Atlantic Oscillation variability on stable isotopes in precipitation, J. Geophys. Res., accepted February 2008. [Abstract, Manuscript, PDF, 1.6MB]

Leave a Reply

Your email address will not be published. Required fields are marked *