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 the direct, strongly nonlinear response of the climate-cryosphere system to the 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 presence of a large continental area with exposed rocks. We show that the sharp peak in the power spectrum of ice volume at 100 kyr period 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.
Orbital forcing and role of the latitudinal insolation/temperature gradient
