Featured Science Paper
Antarctic isotopic thermometer during a CO2 forced warming event
Water isotopes are the prime tool for diagnosing past temperatures from polar ice cores. This is mainly because the isotopic content of precipitation depends on temperature during the condensation process. This leads to a relationship between temperature and ice-core isotope content. A common assumption for ice-core interpretation is that the isotopes measured over either a geographical region or over a time period at one site always show an identical relationship to temperature. Previous work on Greenland ice cores has shown that this assumption can break down under large climate shifts. However, model experiments looking at climate shifts from the last glacial maximum to the present have found that the common geographical/temporal assumption is adequate for Antarctica.
This paper uses a well-studied forced event, the expected future double CO2 warming, to study how Antarctic isotopes react to a warmer climate. The most unexpected and interesting result found is that the temporal gradients in this experiment are far removed from the geographical ones. This finding suggests that we have to expect a rather muted response of water isotopes to a substantial warming event. This may affect estimates of present day Antarctic warming derived from short ice cores. The paper goes further and diagnoses much of the reason for the discrepancy, caused largely by the way that the occurrence of precipitation is related to temperature. This affects how one should calibrate the isotope thermometer, and might affect the way we interpret the climate of past warm periods. This paper is the first one in which Louise Sime uses HADAM3 with its new capability (gained under the QUEST-Deglaciation project) to follow water isotopes.
Sime, L. C., Tindall, J. C., Wolff, E. W., Connolley, W. M. and Valdes, P. J.
J. Geophys. Res., 113, D24119, 2008.