Short fluctuations in Antarctic isotope records: a link with cold events in the North Atlantic?

The recent synchronization of Antarctic and Greenland ice cores obtained by Blunier and colleagues from methane measurements in the 10–15 kyr and 25–45 kyr intervals allows us to investigate leads and lags between climatic changes in the two hemispheres. We observe that most of the cold episodes recorded in the Greenland ice correspond to peaks in isotope Antarctic records once the common timescale derived from methane measurements is adopted. These Antarctic peaks are commonly interpreted as reflecting warmings in Antarctica. Here we draw attention on a possible alternative explanation. Those peaks could, at least partially, correspond to a temporary cooling of the source water providing Antarctic precipitation as a result of cold conditions in the North Atlantic, and of a fast interhemispheric transfer of this cooling via the atmosphere or the ocean. This suggestion would be consistent with recent measurements of the deuterium excess in Vostok ice (Antarctica). Although there are good arguments in favor of the currently accepted interpretation, the influence of temperature changes in the source regions of Antarctic precipitation on the temperature proxy has to be kept in mind when interpreting the phasing between Greenland and Antarctic ice core records.