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 δ18O 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 δ18O ice‐volume proxy records. Key Points Climate responses to orbital changes simulated with an Earth system model Model produces a larger ice‐volume response to obliquity than precession Model results agree with early Pleistocene oxygen isotope records