Preprints
https://doi.org/10.5194/egusphere-2023-2893
https://doi.org/10.5194/egusphere-2023-2893
20 Dec 2023
 | 20 Dec 2023
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

The Largely Linear Response of Earth’s Ice Volume to Orbital Forcing

Liam Wheen, Oscar Benjamin, Thomas Gernon, Cameron Hall, and Jerry Wright

Abstract. Orbital forcing plays a key role in pacing the glacial-interglacial cycles. However, the mechanistic linkages between the orbital parameters — eccentricity, obliquity, and precession — and global ice volume remain unclear. Here, we investigate the effect of Earth’s orbitally governed incoming solar radiation (that is, insolation) on global ice volume over the past 800,000 years. We consider a simple linear model of ice volume that imposes minimal assumptions about its dynamics. We find that this model can adequately reproduce the observed ice volume variations for most of the past 800,000 years, with the notable exception of Marine Isotope Stage 11. This suggests that, aside from a few extrema, the ice volume dynamics primarily result from an approximately linear response to orbital forcing. We substantiate this finding by addressing some of the key criticisms of the orbitally forced hypothesis. In particular, we show that eccentricity can significantly vary the ocean temperature without the need for amplification on Earth. We also present a feasible mechanism to explain the absence of eccentricity’s 400,000 year period in the ice volume data. This requires part of the forcing from eccentricity to be lagged via a slow-responding mechanism, resulting in a signal that closer approximates the change in eccentricity. A physical interpretation of our model is proposed, using bulk ocean and surface temperatures as intermediate mechanisms through which the orbital parameters affect ice volume. These show reasonable alignment with their relevant proxy data, though we acknowledge that these variables likely represent a combination of mechanisms.

Liam Wheen, Oscar Benjamin, Thomas Gernon, Cameron Hall, and Jerry Wright

Status: open (until 23 Mar 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on “The Largely Linear Response of Earth’s Ice Volume to Orbital Forcing”', Mikhail Verbitsky, 21 Dec 2023 reply
    • AC1: 'Reply on CC1', Liam Wheen, 20 Feb 2024 reply
  • CC2: 'Comment on egusphere-2023-2893, regarding the assumptions built into LR04', Bryan C. Lougheed, 04 Jan 2024 reply
    • AC2: 'Reply on CC2', Liam Wheen, 20 Feb 2024 reply
      • CC3: 'Reply on AC2', Bryan C. Lougheed, 29 Feb 2024 reply
        • AC3: 'Reply on CC3', Liam Wheen, 01 Mar 2024 reply
Liam Wheen, Oscar Benjamin, Thomas Gernon, Cameron Hall, and Jerry Wright

Model code and software

Wheen 23 Liam Wheen https://github.com/liamwheen/Wheen_23

Liam Wheen, Oscar Benjamin, Thomas Gernon, Cameron Hall, and Jerry Wright

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Short summary
We look at the impact of Earth's orbital positioning on its ice volume over the past 800,000 years. We first justify that the temperature change observed in ocean temperature proxy data could be explained by variation in the ellipticity of Earth's orbit. From there, we present a simple linear model of global ice volume. We find this to explain the data well in most regions, suggesting that the majority of global ice volume dynamics can be explained by a linear response to orbital variations.