Insolation evolution and ice volume legacies determine interglacial and glacial intensity

Abstract

Abstract. Interglacials and glacials represent low and high ice volume end-members of ice age cycles. While progress has been made in our understanding of how and when transitions between these states occur, their relative intensity has been lacking an explanatory framework. With a simple quantitative model, we show that over the last 800 000 years interglacial intensity can be described as a function of the strength of the previous glacial and the summer insolation at high latitudes in both hemispheres during the deglaciation. Since the precession components in the boreal and austral insolations counteract each other, the amplitude increase in obliquity cycles after 430 000 years ago is imprinted in interglacial intensities, contributing to the manifestation of the so-called Mid-Brunhes Event. Glacial intensity is also linked to the strength of the previous interglacial, the time elapsed from it, and the evolution of boreal summer insolation. Our results suggest that the memory of previous climate states and the time course of the insolation are crucial for understanding interglacial and glacial intensities.

Extreme glacial cooling likely led to hominin depopulation of Europe in the Early Pleistocene

“…1 and table S1) ( 7 ). This dispersal lag may be attributed to a period of cooler interglacials ~1.8 to ~1.6 Ma, which in turn may be related to the 1.2-million-year (Myr) amplitude modulation of the obliquity cycle ( 8 ).…”

Distinguishing Between Insolation‐Driven and Phase‐Locked 100‐Kyr Ice Age Scenarios Using Example Models

“…Naively one often assumes that, at least in the insolation‐driven case, a stronger summer insolation should lead to a larger ice volume loss. This is supported by the finding that the ice volume rate of change (Roe, 2006) and magnitude of termination (Mitsui et al., 2022; Tzedakis et al., 2017) are correlated with different insolation measures. However, we find that there is no statistically significant correlation between the size of the ice volume drop and the termination‐integrated insolation in the observed proxy record or in the models examined.…”

“…We next compare the ice volume drop during terminations to the insolation integrated over the period of termination. On the one hand, Roe (2006) found that dV/dt can be approximated by I(t) throughout time, and Mitsui et al (2022) found that the size of terminations is directly related to the amount of insolation integrated over the caloric summer half of the year. On the other hand, one expects physical processes other than insolation to significantly contribute to the retreat of the ice sheets during terminations (e.g., sea ice shutting off snow accumulation in the SIS mechanism), so it is not obvious that there should be a relation between dV/dt and ice volume change during terminations, specifically.…”

“…This analysis suggests that one cannot use this measure to distinguish between internally-or insolationdriven glacial cycles. Note that this result is affected by our analysis choices, such as defining T6 to include two steps, the choice of insolation measure as opposed to other possibilities (e.g., caloric summer half-year insolation, Mitsui et al, 2022), etc.…”

A gradual change is more likely to have caused the Mid-Pleistocene Transition than an abrupt event

“…To investigate the relative relevance of the three simulations in a quantitative way, we use an objective criterion named the Bayesian Information Criterion (BIC; see Methods). The BIC enables quantifying the relevance of a model against another one [43][44][45] . This criterion is Fig.…”