Tropical timings: more studies find evidence for Earth’s 2.4 million year eccentricity ‘grand cycle’ 

Further to two recent posts, we list a few more published research results that find a ‘~2.4 million year’ (we say ~2.47 myr) grand eccentricity cycle in empirical data.

What we’re proposing over these three posts is that all the long-looking cycles and main sub-periods discussed in the papers can be quantified and matched to each other in small number ratios (see the end of this post).

For more on where and how the eccentricity of Earth fits into its other orbital parameters, see our post:
Tropical Timings: Earth’s two eccentricity cycles.

Paper – Obliquity disruption and Antarctic ice sheet dynamics over a 2.4-Myr astronomical grand cycle (2025).

This study splits the ~2.4 myr cycle into two ~1.2 myr cycles, which alternate in amplitude (this is from the Discussion section):
‘Over the course of the 2.4-Myr grand cycles, eccentricity variance changes substantially and approaches zero during “nodes,” where it remains relatively low for a sustained interval (e.g., 18.8 to 19.2 Ma and 16.4 to 16.8 Ma; Fig. 3A). In contrast, obliquity forcing and its variance are substantial even during long-term 1.2-Myr nodes (41) (Fig. 3B). Theoretical obliquity and eccentricity/precession variance are anti-phased at the million-year scale, and the 1.2-Myr obliquity cycle has a 2.4-Myr modulation, where large 1.2-Myr maxima alternate with smaller maxima (see Fig. 3, A and B). Every ~2.4 Myr, the summertime insolation due to obliquity is the highest and equator-pole temperature gradient is the weakest, at which time loss of sea ice and enhanced upwelling of warm deep ocean water results in melting and retreat of the marine-terminating ice margin. These patterns are characterized in detail in (39), but see also (45, 80).

‘We propose the label “obliquity disruption” for this mechanism, as consecutive intervals of high obliquity every ~2.4 Myr forces ice retreat related to meridional gradient-controlled oceanic heat delivery to marine-terminating margins, even when eccentricity and precession summertime forcing is minimized (e.g., ~19.1 Ma).’ [bold added]

Quote: ‘This work provides insights into the past and future of the Earth’s largest ice sheets.’
Quote: ‘Today, Earth’s obliquity forcing variance is near a 2.4-Myr maximum.’

Under the heading: MATERIALS AND METHODS, the authors give details of the Astrochronology techniques they used.
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A Nature research article – Eccentricity pacing and rapid termination of the early Antarctic ice ages (2024) – by van Peer et al, says:
‘The imprint of eccentricity on δ18Ob is remarkably consistent globally whereas the obliquity signal is inconsistent between sites, indicating that eccentricity was the primary pacemaker of land ice volume.’

It also gives ID numbers to the ‘~2.4 Myr’ eccentricity cycle e.g. here: ‘The analysed time interval spans most of ~2.4-Myr Eccentricity Cycle 12 ‘through to the first half of Eccentricity Cycle 9 (Fig. 3c).
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Another Nature research article –
Deep-sea hiatus record reveals orbital pacing by 2.4 Myr eccentricity grand cycles (2024) – by Dutkiewicz et al, says:
‘Here, we apply spectral analysis to a dataset of Cenozoic deep-sea hiatuses to reveal a ~2.4 Myr eccentricity signal, disrupted by episodes of major tectonic forcing. We propose that maxima in the hiatus cycles correspond to orbitally forced intensification of deep-water circulation and erosive bottom current activity, linked to eccentricity maxima and peaks in insolation and seasonality.’

Also: ‘The fundamental Milankovitch cycles, 19–23 kyr precession, 41 kyr obliquity, and 100 and 400 kyr eccentricity, are modulated by longer orbital cyclicities (e.g., 1.2 Myr, 2.4 Myr, etc.).’
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These are all detailed papers of course, but here we’re just trying to draw attention to a grand eccentricity cycle of over 2.4 million years found in the climate data. This amounts to 6 long eccentricity cycles (of 414*996 tropical years each), also equal to 26 short ones (3:13 ratio of long:short per half-cycle of 1.2 myr, hence the split cited above).

Summary of orbital parameter numbers in the ‘2.4 myr’ grand eccentricity cycle:
Long eccentricity: 6
Short eccentricity: 26
Obliquity: 60
Precession (axial): 96
’23 kyr’ (23*996y): 108
(Ratio of 60:96:108 = 5:8:9)
. . .
Links to all Talkshop tropical timings posts can be found here.
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