Abstract
Abstract. The origin of the 100 kyr cyclicity, which dominates ice volume variations and other climate records over the past million years, remains debatable. Here, using a comprehensive Earth system model of intermediate complexity, we demonstrate that both strong 100 kyr periodicity in the ice volume variations and the timing of glacial terminations during past 800 kyr can be successfully simulated as direct, strongly nonlinear responses of the climate-cryosphere system to orbital forcing alone, if the atmospheric CO2 concentration stays below its typical interglacial value. The existence of long glacial cycles is primarily attributed to the North American ice sheet and requires the presence of a large continental area with exposed rocks. We show that the sharp, 100 kyr peak in the power spectrum of ice volume results from the long glacial cycles being synchronized with the Earth's orbital eccentricity. Although 100 kyr cyclicity can be simulated with a constant CO2 concentration, temporal variability in the CO2 concentration plays an important role in the amplification of the 100 kyr cycles.
Highlights
It is generally accepted that, as postulated by the Milankovitch theory (Milankovitch, 1941), Earth’s orbital variations play an important role in Quaternary climate dynamics, the nature of glacial cycles still remains poorly understood
To clarify whether the 100 kyr cycles directly originate from the orbital forcing, we performed a set of additional experiments with the same orbital forcing as in the BE described above but maintaining a constant CO2 concentration in time
Results of our experiments support the notion that 100 kyr cycles represent a direct, strongly nonlinear response of the climate-cryosphere system to orbital forcing and they are directly related to the corresponding eccentricity period
Summary
It is generally accepted that, as postulated by the Milankovitch theory (Milankovitch, 1941), Earth’s orbital variations play an important role in Quaternary climate dynamics, the nature of glacial cycles still remains poorly understood. One of the major challenges to the classical Milankovitch theory is the presence of 100 kyr cycles that dominate global ice volume and climate variability over the past million years (Hays et al, 1976; Imbrie et al, 1993; Paillard, 2001). This periodicity is practically absent in the principal “Milankovitch forcing” – variations of summer insolation at high latitudes of the Northern Hemisphere (NH). Since a number of conceptual models based on fundamentally different assumptions were able to reproduce reconstructed ice volume variations with similar skill, it became clear that a further advance in understanding of 100 kyr cyclicity requires physically-based models
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