Geosciences (Nov 2023)
Global Evidence of Obliquity Damping in Climate Proxies and Sea-Level Record during the Last 1.2 Ma: A Missing Link for the Mid-Pleistocene Transition
Abstract
A recent research has identified an inverse amplitude link between obliquity damping and short eccentricity amplification during the Mid-Late Pleistocene based on LR04 δ18O and equatorial Pacific Site 846 sea surface temperature records that is associated with the Earth’s long-term cooling. In the present study, new evidence of this anticorrelation is presented from Antarctic δD-CO2-CH4 records, global benthic–planktic δ18O, and regional (Atlantic, Pacific, Mediterranean, and Indian) climate-related proxies. Based on a critical review of theoretical constraints (Earth’s oblateness changes and ice-volume phase lag in the obliquity band <5.0 kyr), this widespread and symmetric (bipolar) obliquity response damping has been interpreted as an effect of the obliquity–oblateness feedback, which could be the latent physical mechanism at the origin of the Mid-Pleistocene Transition (MPT). Indeed, results and considerations of the present work suggest that fast and positive/negative net variation in the Earth’s oblateness in the obliquity band was controlled by a dominant glacio-eustatic water mass component and, assuming a rapid response of the ice volume to surface temperature changes, the mean obliquity lag response is estimated to be <5.0 kyr over the past 800 kyr. These elements may explain the interglacial/glacial damping observed in the obliquity response. The consolidation of the Earth’s long-term icy state in the subtrend IV, culminating with the post-MPT obliquity damping, might have contributed to the strengthening of the short eccentricity response by mitigating the obliquity ‘ice killing’ during obliquity maxima (interglacials), favouring the obliquity-cycle skipping and a feedback-amplified ice growth in the short eccentricity band (obliquity damping hypothesis). This suggests a different impact of the climate friction than what is generally believed, which is presumably the latent physical mechanism that triggers the transient ‘competitive’ interaction between obliquity and short eccentricity started early during the Piacenzian.
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