Net effect of ice-sheet-atmosphere interactions reduces simulated transient Miocene Antarctic ice sheet variability

Benthic δ¹⁸O levels vary strongly during the warmer-than-modern early- and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO₂ levels and orbital settings. Earlier transient simulations lacked ice-sheet-atmosphere interactions, and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet-atmosphere interactions, running IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO₂ levels (between 280 and 840 ppm) as well as varying ice sheet configurations (between no ice and a large East Antarctic ice sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo-temperature feedback, partly compensated by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO₂ and ice volume. Together, these ice-sheet-atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations. Forced by quasi-orbital 40-kyr forcing CO₂ cycles, the ice volume variability reduces by 21% when ice-sheet-atmosphere interactions are included, compared to when forcing variability is only based on CO₂ changes. Thereby, these interactions also diminish the contribution of AIS variability to benthic δ¹⁸O fluctuations. Evolving bedrock topography during the early- and mid-Miocene reduces ice volume variability by 10%, under equal 40-kyr cycles of atmosphere and ocean forcing.