A novel method to study the phase relationship between Antarctic and Greenland climate

A classical method for understanding the coupling between northern and southern hemispheres during millennial-scale climate events is based on the correlation between Greenland and Antarctic ice core records of atmospheric composition. Here we present a new approach based on the use of a single Antarctic ice core in which measurements of methane concentration and inert gas isotopes place constraints on the timing of a rapid climate change in the North and of its Antarctic counterpart. We applied it to the Marine Isotope Stage (MIS) 5d/c transition early in the last glaciation similar to108 ky BP. Our results indicate that the Antarctic temperature increase occurred 2 ky before the methane increase, which is used as a time marker of the warming in the Northern Hemisphere. This result is in agreement with the "bipolar seesaw'' mechanism used to explain the phase relationships documented between 23 and 90 ky BP [Blunier and Brook, 2001].