EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Investigating precession cancellation across the MPT using a zonally averaged energy balance model

Daniel Gunning
Daniel Gunning
  • University of Bergen, Faculty of Mathematics and Natural Sciences, Department of Earth Sciences, Norway (

The precession of the equinoxes has a strong influence on the intensity of summer insolation according to most metrics and we would therefore expect the 23-Kyr and 19-Kyr precession cycles to be strongly reflected in our records of global ice volume, if summer insolation is indeed important for pacing glacial-interglacial cycles as proposed by Milutin Milankovitch. Instead, the precession signal is reduced in amplitude compared with the obliquity cycle in the Late Pleistocene, and in the Early Pleistocene (EP) precession appears completely absent in the δ18O stack. For this reason, the ‘40-Kyr world’ of the EP has been referred to as Milankovitch's other unsolved mystery. Indeed, numerous models of the Northern Hemisphere (NH) ice sheets simulated across the Plio-Pleistocene predict both a strong precessional and obliquity variability during the EP, at odds with the δ18O record. This points to the possibility of a dynamic Antarctic Ice Sheet in the EP that varied out-of-phase with the NH ice sheets at the precession period. In the original theory proposed by Raymo et al., (2006), from 3 to 1 Ma the East Antarctic Ice Sheet may have been land-terminating between 70S to 65S and sensitive to local summer insolation forcing. As precession is out-of-phase between the hemispheres, these variations could be cancelled out in globally integrated proxies of sea-level, concealing the true precession variability of both hemispheres in the marine sediment record. While studies have demonstrated  that precession-driven variations of the Antarctic Ice Sheet could cancel out NH variations in the deep-ocean record, no studies have investigated the actual feasibility of strong precession variability of the Antarctic Ice Sheet in the EP driven by local summer insolation, and whether it would have the magnitudes necessary to offset larger variations of the NH ice sheets. The question remains under what CO2 concentrations and orbital configuration can the East Antarctic Ice Sheet realistically be sensitive to local summer insolation forcing and possibly deglaciated from 70S to 65S, as postulated by Raymo et al. (2006). Can this produce the 10-30 m of sea-level necessary to offset NH variations in ice volume? To investigate the feasibility for anti-phased precession variability between the NH ice sheets and Antarctica in the EP, we use a zonally-averaged energy balance model coupled to a 1-D ice sheet model of a northern and southern hemisphere ice sheet, forced by atmospheric CO2 concentrations and daily insolation fields. The model will simulate glacial cycles across the Quaternary for different CO2 scenarios and determine whether anti-phased precessional cycles in ice volume between the hemispheres is a viable mechanism to explain the 40-Kyr world found in the δ18O record.

How to cite: Gunning, D.: Investigating precession cancellation across the MPT using a zonally averaged energy balance model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7385,, 2023.