How obliquity cycles powered early Pleistocene global ice-volume variability

Milankovitch theory proposes that the magnitude of high-latitude summer insolation dictates the continental ice-volume response by controlling summer snow melt, thus anticipating a substantial ice-volume contribution from the strong summer insolation signal of precession. Yet almost all of the early Pleistocene O-18 records' signal strength resides at the frequency of obliquity. Here we explore this discrepancy using a climate-vegetation-ice sheet model to simulate climate-ice sheet response to transient orbits of varying obliquity and precession. Spectral analysis of our results shows that despite contributing significantly less to the summer insolation signal, almost 60% of the ice-volume power exists at the frequency of obliquity due to a combination of albedo feedbacks, seasonal offsets, and orbital cycle duration differences. Including eccentricity modulation of the precession ice-volume component and assuming a small Antarctic ice response to orbital forcing produce a signal that agrees with the O-18 ice-volume proxy records.