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 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 about ~180 ppmv or between 3.5 °C and 5.5 °C, depending only weakly on the bedrock elevation dataset. Excluding the solid Earth feedback decreases the hysteresis effect significantly towards ~40 ppmv, because the transition to a glacial state can occur at a higher forcing. 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.