The intensification of glaciation in the mid-Pliocene and the Earth's obliquity variation

The intensification of glaciation in the northern hemisphere during the past 3 Myr has clearly been confirmed by δ¹⁸O record for deep-sea sediment cores extending over the past 5-6 Myr. For earth models with a lower mantle viscosity of greater than 10²² Pa s inferred from several geophysical observables, perturbations in the Earth's dynamic ellipticity in response to this long term climatic change might have produced an increase of the average Earth's obliquity 0.06°through the resonant effect associated with the orbits of Jupiter and Saturn. This predicted obliquity change may consequently operate as a negative feedback on solar insolation, resulting in a reduction of the intensification of glaciation.