THE INTENSIFICATION OF GLACIATION IN THE MID-PLIOCENE AND THE EARTHS OBLIQUITY VARIATION

The intensification of glaciation in the northern hemisphere during th e past 3 Myr has clearly been confirmed by delta(18)O record for deep- sea sediment cores extending over the past 5-6 Myr. For earth models w ith a lower mantle viscosity of greater than 10(22) pa, inferred from several geophysical observables, perturbations in the Earth's dynamic ellipticity in response to this long term climatic change might have p roduced an increase of the average Earth's obliquity 0.06 degrees thro ugh the resonant effect-associated with the orbits of Jupiter and Satu rn. This predicted obliquity change may consequently operate as a nega tive feedback on solar insolation, resulting in a reduction of the int ensification of glaciation.