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Cancellation of the precessional cycle in δ18O records during the Early Pleistocene
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  • Anne Moree,
  • Tianyi Sun,
  • Anais Bretones,
  • Eivind Straume,
  • Kerim Nisancioglu,
  • Geoffrey Gebbie
Anne Moree
Geophysical Institute, University of Bergen and the Bjerknes Centre for Climate Research

Corresponding Author:[email protected]

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Tianyi Sun
Institute for Geophysics, Jackson School of Geosciences, the University of Texas at Austin
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Anais Bretones
Department of Earth Science, University of Bergen and the Bjerknes Centre for Climate
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Eivind Straume
Centre for Earth Evolution and Dynamics (CEED)
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Kerim Nisancioglu
University of Bergen and the Bjerknes Centre for Climate Research
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Geoffrey Gebbie
Woods Hole Oceanographic Institute
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Abstract

Deep-sea δ18O records show a pronounced difference in Milankovitch periodicity between the Early and Late Pleistocene. δ18O is interpreted as a proxy for ice sheet volume and temperature, which led to the conclusion that glacial-interglacial cycles considerably changed their rhythm during the mid-Pleistocene. This transition is referred to as the mid-Pleistocene Transition (MPT). Specifically, the precessional component of the Milankovitch cycles is absent in Early Pleistocene δ18O records, despite its continuous presence in solar insolation forcing to the ice sheets. Climate feedbacks involving (sea) ice, geological processes and carbon and nutrient cycling have been proposed as causes of this marked change. We however show that the absence of an Early Pleistocene precession signal in deep-sea δ18O records could be the result of destructive interference of the precessional cycle in the interior ocean. Such cancellation is caused by the anti-phasing of the precessional cycle between the North Atlantic and Southern Ocean deep-water sources (see Figure). We explore the potential for cancellation in the transient setup of the Total Matrix Intercomparison model for a wide range of source signal strengths. Our results show that cancellation can cause the absence of the precessional signal due to cancellation in the interior South-Atlantic, Indian and Pacific basins. Cancellation is especially widespread for a relative end-member contribution typical for the Early Pleistocene. We therefore conclude that the precessional component is likely incompletely archived in Early Pleistocene δ18O records, and appears as an actual change in Milankovitch periodicity across the MPT. Proxies not susceptible to cancellation of precession (such as those currently retrieved across the MPT from Antarctica) would be able to verify to what extent deep-sea δ18O correctly represents Pleistocene climate.
16 Feb 2021Published in Geophysical Research Letters volume 48 issue 3. 10.1029/2020GL090035