Interglacials of the Quaternary defined by northern hemispheric land ice distribution outside of Greenland

Peter Köhler,Roderik S W Van De Wal

doi:10.1038/s41467-020-18897-5

Abstract

Glacial/interglacial dynamics during the Quaternary were suggested to be mainly driven by obliquity (41-kyr periodicity), including irregularities during the last 1 Myr that resulted in on average 100-kyr cycles. Here, we investigate this so-called Mid-Pleistocene Transition via model-based deconvolution of benthic δ18O, redefining interglacials by lack of substantial northern hemispheric land ice outside of Greenland. We find that in 67%, 88% and 52% of the obliquity cycles during the early, middle and late Quaternary, respectively, a glacial termination is realized leading to irregular appearances of new interglacials during various parts of the last 2.6 Myr. This finding suggests that the proposed idea of terminations leading to new interglacials in the Quaternary as obliquity driven with growing influence of land ice volume on the timing of deglaciations during the last 1 Myr might be too simple. Alternatively, the land ice-based definition of interglacials needs revision if applied to the entire Quaternary.

Highlights

Glacial/interglacial dynamics during the Quaternary were suggested to be mainly driven by obliquity (41-kyr periodicity), including irregularities during the last 1 Myr that resulted in on average 100-kyr cycles
One of the most recent approaches to explain the observed pattern during the MPT24 (T17 in the following) developed a simple rule by which the onset of new interglacial periods during the last 2.6 Myr are identified based on caloric summer half-year insolation at 65°N, whereby it assumes that deglaciations mainly depend on local summer insolation
One study[6] deconvolved the same benthic δ18O stack[4] used in T17 into its sea level and temperature components by applying physically consistent 3-D land ice models and came up with the simulated temporal evolution of land ice distribution. They concluded that after the Mid-Pleistocene Transition (MPT) the longer glacial cycles with larger amplitudes in sea-level change seemed to be controlled by North American land ice dynamics: when growing to a certain size, the Laurentide and Corrdilleran ice sheets merge to a single dome, which supports thicker ice sheets

Summary

Results

The detrending of the LR04 δ18O applied in T17 is according to our results too imprecise to correct as suggested for the effects of deep ocean temperature and ice volume in Antarctica and Greenland (Fig. 4b) By our definition, this turns the obliquity cycles containing MIS 55, 61, 65, 71, 79, 93, and 101 into periods without the onset of a new interglacial. Our definition of interglacials clearly illustrates a shift in the climate system, from an interglacial-dominated period in the early Quaternary to a glacial-dominated period in the late Quaternary, a pattern which has originally been suggested from results of a simplified vertically integrated sectorial ice model without thermodynamics[28] This becomes especially clear when we base our findings on constant thresholds (e.g., Fig. 3c). The authors were able to simulate climate dynamics across the MPT confirming a dominant role of regolith removal on glacial

Ice cores Allan hills blue ice

Methods

Code availability