Abstract
Over the Quaternary, the ice volume variations are “paced” by the astronomy. However, the precise way in which the astronomical parameters influence the glacial-interglacial cycles is not clear. The origin of the 100 kyr cycles over the last million year and of the switch from 40 kyr to 100 kyr cycles over the Mid Pleistocene Transition remain largely unexplained. By representing the climate system as oscillating between two states, glaciation and deglaciation, switching once a glaciation and a deglaciation thresholds are crossed, the main features of the ice volume record can be reproduced (Parrenin and Paillard, 2012). However, previous studies have only focused on the use of a single summer insolation as input. Here, we use a simple conceptual model to test and discuss the influence of the use of different summer insolation forcings, having different contributions from precession and obliquity, on the model results. We show that some features are robust. Specifically, to be able to reproduce the frequency shift over the Mid Pleistocene Transition, the deglaciation threshold needs to increase over time, independently of the summer insolation used as input. The quality of the model data agreement however depends on the chosen type of summer insolation and time period considered.
Highlights
To be able 10 to reproduce the frequency shift over the Mid Pleistocene Transition, the deglaciation threshold needs to increase over time, independently of the summer insolation used as input
The implicit assumption 85 is made that the global ice volume changes are mainly driven by the Northern Hemisphere ice sheet waning and waxing, as we focus on the effect of insolation changes at high northern latitudes
The idea that the deglaciation threshold is linked to both, insolation and ice volume, is not new (Parrenin and Paillard, 2003, 2012), and is similar to the one developed by Tzedakis et al (2017), where the threshold for a complete deglaciation 105 decreases with time as the system accumulates instability with ice sheets becoming more sensitive to insolation increase
Summary
Paleoclimate records over the Quaternary (last 2.6 Myr), such as ice cores (Jouzel et al, 2007) or marine cores (Lisiecki and 15 Raymo, 2005) show a succession of oscillations. We are able to reproduce a switch from 41 kyr oscillations before the MPT to 100 kyr cycles afterwards in agreement with the records for all insolation forcings, by varying a single parameter : the deglaciation threshold V0. This is similar to the results of Paillard (1998) who obtained a frequency shift on the glacial cycles by using a linearly increasing deglaciation threshold. This is coherent with the more recent results of Tzedakis et al (2017), which demonstrated that the particular sequence of interglacials that happened over the Quaternary and the frequency shift from 41 to 100 kyr could be explained with a simple rule, taking into account a deglaciation threshold that increases over time, leading to ’skipped’ insolation peaks and longer cycles
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