The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles

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 CO 2 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 CO 2 concentration, temporal variability in the CO 2 concentration plays an important role in the amplification of the 100 kyr cycles.

Deglacial ice sheet meltdown: orbital pacemaking and CO<sub>2</sub> effects

“…However, our model results also illustrate that orbital forcing alone was not sufficient, and that the ∼ 100 ppmv CO 2 rise needs to be taken into account to explain the fast and full retreat of the North American and Eurasian ice sheets during the deglaciation. This supports previous model studies, which have identified GHG variations as an important contributor to Pleistocene glacial cycles (Gallée et al, 1992;Yoshimori et al, 2001;Ganopolski and Calov, 2011;AbeOuchi et al, 2013). And the results emphasize how important it is to identify the mechanisms responsible for the orbitalscale modulation of atmospheric CO 2 concentrations (Kohfeld and Ridgwell, 2009;Tagliabue et al, 2009;Chikamoto et al, 2012;Menviel et al, 2012;Brovkin et al, 2012).…”

“…On the other hand, the reduction of dust deposition rates on snow and ice during the deglaciation may have been a negative feedback process. Previous studies with the coupled ice sheet-climate model CLIMBER-2, including a dust model, indicated that aeolian dust feedbacks played an important role during glacial cycles Ganopolski and Calov, 2011).…”

“…It was demonstrated, however, that the carbon cycle feedbacks played an important role during the last deglaciation and the Quaternary Period (last ∼ 2.6 million years), amplifying glacial-interglacial cycles (Gallée et al, 1992;Yoshimori et al, 2001;Ganopolski and Calov, 2011;Abe-Ouchi et al, 2013). Still, their role in triggering and promoting the climate change and ice sheet retreat during the last deglaciation has not been firmly established.…”

“…The ice sheet response to the simulated climate feedbacks, such as the elevation-desert effect (Yamagishi et al, 2005), ice albedo and stationary wave feedbacks (Roe and Lindzen, 2001;Abe-Ouchi et al, 2013), and ocean circulation changes (Gildor and Tziperman, 2000) were not represented. To account for the ice sheet-climate interactions, numerical models of varying complexity have been employed, including zero-dimensional conceptual models (Imbrie and Imbrie, 1980;Paillard, 1998), box models (Gildor and Tziperman, 2000), two-dimensional zonally averaged coupled climate-ice sheet models (Gallée et al, 1992), a threedimensional ice sheet model driven by climatic parameterizations derived from an atmosphere-ocean general circulation model (Abe-Ouchi et al, 2007, and a threedimensional ice sheet model coupled to an earth system model of intermediate complexity Ganopolski and Calov, 2011). To our knowledge, the transient effects of orbital parameter changes and carbon cycle feedbacks during the last deglaciation have not been previously quantified in a coupled ice sheet-climate model with three-dimensional ice sheet, atmosphere, and ocean components.…”

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…Second, temporal development of ice-age cycles provides critical information about the nature of long-term climate cooling over the past few million years, in response to CO 2 reduction and interactions among ice, land cover, and climate (e.g., Clark et al, 2006;K€ ohler and Bintanja, 2008;de Boer et al, 2010de Boer et al, , 2012Hansen et al, 2013). Third, variable amplitude of individual ice ages helps to determine the relationship between climate change, astronomical climate forcing cycles, and climate feedbacks on timescales of 10se100s of kiloyears (e.g., Oglesby, 1990;Imbrie et al, 1993;Raymo et al, 2006;Colleoni et al, 2011Colleoni et al, , 2016Ganopolski and Calov, 2011;Carlson and Winsor, 2012;Abe-Ouchi et al, 2013;Hatfield et al, 2016;Liakka et al, 2016). Fourth, the size and spatial distribution of land ice during past glacials determines crustal rebound processes when ice masses melt, which in turn affects sea-level reconstructions for subsequent interglacials.…”