How variations in Earth's orbit pace the glacial-interglacial cycles of
the Quaternary are probably one of the greatest mysteries of modern
climate science. Supposing coevolution of climate, ice sheets, and
carbon cycle over the past 3 million years a current theory cannot
explain the observations when it is driven by orbital variations as the
only external forcing. Taking advantage of the alkenone paleothermometer
in sediment cores sampled in the Tasman Sea floor, we show that the
transition of glacial-interglacial periods from 41,000- to 100,000-year
that happened during the mid-Pleistocene is not singular. A similar
transition involving 10 times longer periods occurred at the hinge of
Pliocene-Pleistocene. Referring to the recent theory of gyral Rossby
waves we put forward the idea that the climate system preferentially
responds to certain orbital variations according to subharmonic modes,
which is inherited from the resonant forcing of Rossby waves wrapping
around the subtropical gyres.