Observed and modeled controls on precipitation δ18O over Europe: From local temperature to the Northern Annular Mode

Abstract

Stable isotopes of oxygen and hydrogen are important paleoclimate indicators and can be obtained from many different natural archives in Europe such as tree rings and speleothems. In this study, a comparison was made of controls on European precipitation δ18 O between observations from the Global Network of Isotopes in Precipitation and from the NASA Goddard Institute for Space Studies ModelE general circulation model. In both observations and the general circulation model, the local temperature effect was identified and extended outside of Europe. This temperature control, in turn, was related to a North Atlantic Oscillation-like dipóle but with centers of action different than standard NAO definitions. An examination of midtropospheric circulation controls showed that European δ18O in fact reflects the hemisphere-wide teleconnections associated with the Northern Annular Mode. Seasonal differences were found in the strength of all controls on δ18O, with the annual controls being the combination of strong winter and weak summer controls. The weaker temperature effect in summer is well-known and has been universally attributed to the effects of continental moisture recycling, but the results of this study show that an additional factor is the reduced variability in summertime atmospheric circulation. The strong agreement between observed and modeled controls can help to improve interpretations of paleoclimatic archives of δ18O, particularly in terms of shifts in atmospheric circulation. Copyright 2010 by the American Geophysical Union.