Ocean's likely roles in determining the change of dominant period of Pleistocene glacial cycles?

Hönisch, B. et al.(Science 2009) mentioned that the dominant period of Pleistocene glacial cycles changed during the mid-Pleistocene from 40,000 years to 100,000 years, for as yet unknown reasons.Their reconstruction of the sea surface pCO2 shows a close relationship between atmospheric CO2 concentration and global climate but the drawdown of atmospheric CO2 was not the main cause of the climate transition.

Could the ocean circulation play some roles in this process? The bathymetry changed? The tidal strength changed due to the orbit variation? If so, could the ocean mixing change? Since the ocean mixing is supposed to play essential roles in determining the overturning circulation, ocean mixing pattern changed could then result in overturning circulation change, which would induce variation of heat transport? Finally ~