Hysteresis and orbital pacing of the early Cenozoic Antarctic ice sheet

Abstract. The hysteresis behaviour of ice sheets arises because of the different thresholds for growth and decline of a continental-scale ice sheet depending on the initial conditions. In this study, the hysteresis effect of the early Cenozoic Antarctic ice sheet to different bedrock elevations is investigated with an improved ice sheet–climate coupling method that accurately captures the ice–albedo feedback. It is shown that the hysteresis effect of the early Cenozoic Antarctic ice sheet is ∼180 ppmv or between 3.5 and 5 ∘C, depending only weakly on the bedrock elevation dataset. Excluding isostatic adjustment decreases the hysteresis effect significantly towards ∼40 ppmv because the transition to a glacial state can occur at a warmer level. The rapid transition from a glacial to a deglacial state and oppositely from deglacial to glacial conditions is strongly enhanced by the ice–albedo feedback, in combination with the elevation–surface mass balance feedback. Variations in the orbital parameters show that extreme values of the orbital parameters are able to exceed the threshold in summer insolation to induce a (de)glaciation. It appears that the long-term eccentricity cycle has a large influence on the ice sheet growth and decline and is able to pace the ice sheet evolution for constant CO2 concentration close to the glaciation threshold.