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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-43
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-43
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Apr 2019

Research article | 24 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Bispectra of climate cycles show how ice ages are fuelled

Diederik Liebrand1 and Anouk T. M. de Bakker2 Diederik Liebrand and Anouk T. M. de Bakker
  • 1Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
  • 2LIttoral ENvironnement et Sociétés (LIENSs), Université de La Rochelle, La Rochelle, France

Abstract. The increasingly nonlinear response of the climate-cryosphere system to insolation forcing during the Pliocene and Pleistocene, as recorded in benthic foraminiferal stable oxygen isotope ratios (δ18O), is marked by a distinct evolution in ice-age cycle frequency, amplitude, phase, and geometry. To date, very few studies have thoroughly investigated the nonsinusoidal shape of these climate cycles, leaving precious information unused to further unravel the complex dynamics of the Earth's system. Here, we present higher-order spectral analyses of the LR04 δ18O stack that describe coupling and energy exchanges among astronomically-paced climate cycles during the Pliocene and Pleistocene. These advanced bispectral computations show how energy is passed from precession-paced to obliquity-paced climate cycles during the Early Pleistocene (~ 2,500–~ 750 ka), and ultimately to eccentricity-paced climate cycles during the Middle and Late Pleistocene (from ~ 750 ka onward). They also show how energy is transferred among many cycles that have no primary astronomical origin. We hypothesize that the change of obliquity-paced climate cycles during the mid-Pleistocene transition (~ 1,200–~ 600 ka), from being a net sink into a net source of energy, is indicative of the passing of a land-ice mass-loading threshold in the Northern Hemisphere (NH), after which cycles of crustal depression and rebound started to resonate with the ~ 110-kyr eccentricity modulation of precession. However, precession-paced climate cycles remain persistent energy providers throughout the Late Pliocene and entire Pleistocene, which is supportive of a dominant and continuous fuelling of the NH ice ages by insolation in the (sub-) tropical zones, and the control it exerts on meridional heat and moisture transport through atmospheric and oceanic circulation.

Diederik Liebrand and Anouk T. M. de Bakker
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Status: open (until 24 Jul 2019)
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Diederik Liebrand and Anouk T. M. de Bakker
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Latest update: 18 Jul 2019
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Short summary
We present a new analysis and interpretation of a well-established climate record that spans the past five million years. We describe how the energy the Earth receives from the sun is transferred among climate cycles with different durations. This analysis offers new insights in the complex evolution of the global climate system and land-ice volumes during this time. Furthermore, it provides a more complete solution to the long-standing 40,000 and ~ 100,000-year problems of the ice ages.
We present a new analysis and interpretation of a well-established climate record that spans the...
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