The 100 kyr cycle of deglaciation during the last 450 kyr: a new interpretation of oceanic and ice core data

Evolution of global ice volume over the last 2.5 Myr is examined using high resolution δ18O records from deep sea cores in the Atlantic and Pacific oceans. Prior to 0.9 Myr BP, δ18O variations occur almost exclusively at the 41 kyr frequency. An increase in δ18O amplitudes is observed after 0.73 Myr BP accompanied by the 100, 41, 23 and 19 kyr frequencies. The deep sea δ18O records and temperature records from Vostok ice cores show similar variations linked to the movement of planets as described by the astronomical theory. The 100 kyr frequency is equal to 124 kyr for the last two glaciations, and 83 kyr for the earlier two glaciations. The appearance of 23 and 19 kyr frequencies after 0.73 Myr indicates that the equatorial bulge of the Earth responsible for this forcing seems to be a recent geological phenomenon. The deglaciations over the 450 kyr BP would result from a change of orbital forcing and a weaker climate coupling of the hemispheres. The northern orbital forcing (41 and 23 kyr frequencies) would be replaced by the obliquity forcing (41 frequency). The succession of these two orbital forcings seems to be similar for the last four glaciations.