Associations between d18O of Water and Climate Parameters in a Simulation of Atmospheric Circulation for 1979-95

David Noone¹ and Ian Simmonds

School of Earth Sciences, University of Melbourne, Parkville, Victoria, Australia

Abstract

The Melbourne University spectral atmospheric general circulation model is adapted to include prediction of stable water isotopes. The new scheme performs well when the modeled d18O of precipitation is compared to both monthly observations from a global network and high-frequency measurements from two neighboring southern Australian sites. The associations between the modeled isotopic signal, temperature, and precipitation are examined on a variety of timescales by exploring the spatial distribution of temporal partial correlations. In contrast to the view commonly taken in paleoclimate studies, typically less than 20% of d18O variance can be explained by temperature changes. The association with temperature is strongest when daily data are considered while the precipitation is more important on longer (interannual) timescales. This shows that as information about individual events is lost through the averaging process, simple distillation models, which have a strong theoretical temperature dependence, become less applicable. It is suggested that reconstruction of precipitation is more reliable on timescales longer than those considered, and the temperature dependence of precipitation facilitates an association between temperature and d18O in proxy records. The small magnitudes of the correlation coefficients suggest that direct interpretation of proxy records such as temperature, or precipitation, should proceed under utmost scrutiny because reconstruction is far more complex than the simple problem of local regression. Specifically, should strong associations with temperature or precipitation exist, it is only partially due to the phenomenological covariance at the deposition site. As such, relationships used for paleoclimate reconstruction that incorporate information about the origin and condensation history of the moisture should be encouraged in place of overly simplistic relationships that involve just local conditions.

Manuscript received 7 October 2001, in final form 28 March 2002

¹ Now at Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA