Natural periodicities and north–south hemispheres connection of fast temperature changes during the last glacial period: EPICA and NGRIP revisited

We investigate both the European Project for Ice Coring in Antarctica (EPICA) and North Greenland Ice-Core Project (NGRIP) datasets to study the time evolution of the so-called Dansgaard–Oeschger events during the last glacial period. The Empirical 5 Mode Decomposition (EMD) is used to extract the proper modes of both the datasets. It is shown that the time behaviour of Dansgaard–Oeschger events is captured by three EMD modes, while three more EMD modes can be used to describe the evolution at longer time scales. Using EMD signal reconstructions and a simple model based on the one-dimensional Langevin equations, it is argued that the occurrence of a Dansgaard– 10 Oeschger event can be described as an excitation of the climate system within the same state, while the longer time scale behaviour appears to be due to transitions between different states. Finally, on the basis of a cross-correlation analysis performed on EMD reconstructions, evidence is presented that the Antarctic climate changes lead that of Greenland by a lag of 3.6 kyr.