A theory of Pleistocene glacial rhythmicity

• Published in: Earth System Dynamics
• Main Authors: Verbitsky, Mikhail Y., Crucifix, Michel, Volobuev, Dmitry M.
• Other Authors: UCL - SST/ELI/ELIC - Earth & Climate
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2018
• Subjects: General Earth and Planetary Sciences; Ice Sheet
• Online Access: http://hdl.handle.net/2078.1/204290; https://doi.org/10.5194/esd-9-1025-2018

Variations in Northern Hemisphere ice volume over the past 3 million years have been described in numerous studies and well documented. These studies depict the mid-Pleistocene transition from 40kyr oscillations of global ice to predominantly 100kyr oscillations around 1 million years ago. It is generally accepted to attribute the 40kyr period to astronomical forcing and to attribute the transition to the 100kyr mode to a phenomenon caused by a slow trend, which around the mid-Pleistocene enabled the manifestation of nonlinear processes. However, both the physical nature of this nonlinearity and its interpretation in terms of dynamical systems theory are debated. Here, we show that ice-sheet physics coupled with a linear climate temperature feedback conceal enough dynamics to satisfactorily explain the system response over the full Pleistocene. There is no need, a priori, to call for a nonlinear response of the carbon cycle. Without astronomical forcing, the obtained dynamical system evolves to equilibrium. When it is astronomically forced, depending on the values of the parameters involved, the system is capable of producing different modes of nonlinearity and consequently different periods of rhythmicity. The crucial factor that defines a specific mode of system response is the relative intensity of glaciation (negative) and climate temperature (positive) feedbacks. To measure this factor, we introduce a dimensionless variability number, V. When positive feedback is weak (V ∼ 0), the system exhibits fluctuations with dominating periods of about 40kyr which is in fact a combination of a doubled precession period and (to smaller extent) obliquity period. When positive feedback increases (V ∼ 0.75), the system evolves with a roughly 100kyr period due to a doubled obliquity period. If positive feedback increases further (V ∼ 0.95), the system produces fluctuations of about 400kyr. When the V number is gradually increased from its low early Pleistocene values to its late Pleistocene value of ...