A phase-space model for Pleistocene ice volume

We present a phase-space model that simulates Pleistocene ice volume changes based on Earth's orbital parameters. Terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for Late Pleistocene terminations. The average phase at which model terminations begin is approximately 90 ± 90∘ before the maxima in all three orbital cycles. The large variability in phase is likely caused by interactions between the three cycles and ice volume. Unlike previous ice volume models, this model produces an orbitally driven increase in 100-kyr power during the mid-Pleistocene transition without any change in model parameters. This supports the hypothesis that Pleistocene variations in the 100-kyr power of glacial cycles could be caused, at least in part, by changes in Earth's orbital parameters, such as amplitude modulation of the 100-kyr eccentricity cycle, rather than changes within the climate system.

Research highlights
► Phase-space model simulates Pleistocene ice volume from Earth's orbital parameters.
► Direct orbital forcing is separated from internal forces of change.
► Threshold for terminations is a combination of ice volume and its rate of change.
► Model exhibits an increase in 100-kyr power at the mid-Pleistocene transition.