Links between CO₂, glaciation and water flow: reconciling the Cenozoic history of the Antarctic Circumpolar Current

Abstract

Abstract. The timing of the onset of the Antarctic Circumpolar Current (ACC) is a crucial event of the Cenozoic because of its cooling and isolating effect over Antarctica. It is intimately related to the glaciations occurring throughout the Cenozoic from the Eocene–Oligocene (EO) transition (≈34 Ma) to the middle Miocene glaciations (≈13.9 Ma). However, the exact timing of the onset remains debated with evidence for a late Eocene set up contradicting others data pointing to an occurrence closer to the Oligocene–Miocene (OM) boundary. In this study, we show the potential impact of the Antarctic ice sheet on the initiation of a proto-ACC at the EO boundary. Our results reveal that the regional cooling effect of the ice sheet increases the sea ice formation, which disrupts the meridional density gradient in the Southern Ocean and leads to the onset of a circumpolar current and its progressive strengthening. We also suggest that subsequent variations in atmospheric CO2, ice sheet volumes and tectonic reorganizations may have affected the ACC intensity after the Eocene–Oligocene transition, which in turn may provide an explanation for the second initiation of the ACC at the Oligocene–Miocene boundary and may reconcile evidence supporting both early Oligocene and early Miocene onset of the ACC.