Response of Late-Eocene warmth to incipient glaciation on Antarctica

• Main Authors: Vermeulen, Dennis H.A., Baatsen, Michiel L. J., Heydt, Anna S.
• Format: Text
• Language: English
• Published: 2024
• Subjects: Antarc*; Antarctic; Antarctica; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-2024-30; https://cp.copernicus.org/preprints/cp-2024-30/

The Eocene-Oligocene Transition (EOT) is marked by a sudden δ 18 O excursion occurring in two distinct phases, ~500 ky apart. These phases signal a shift from the warm Middle- to Late-Eocene greenhouse climate to cooler conditions, with global surface air temperatures decreasing by 3–5 °C and the emergence of the first continent-wide Antarctic Ice Sheet (AIS). While ice-sheet modelling suggests that ice sheet growth can be triggered by declining p CO 2 , it still remains unclear how this transition has been initiated, in particular the first growth phase that seems to be related to oceanic and atmospheric cooling rather than ice sheet growth. Recent climate model simulations of the Late-Eocene show improved accuracy but depict climatic conditions that are not conducive to the survival of incipient ice sheets throughout the summer season. This study therefore examines whether it is plausible to develop ice sheets of sufficient scale to trigger the feedback mechanism(s) required to disrupt the atmospheric regime above the Antarctic continent during warm Late-Eocene summers and establish more favourable conditions for ice expansion. We thereby aim to assess the stability of an incipient AIS under varying radiative, orbital and cryospheric forcing. To do so, we evaluate Community Earth System Model 1.0.5 simulations, using a 38 Ma geo- and topographical reconstruction, considering different radiative (4 and 2 pre-industrial carbon) and orbital (present-day and low summer insolation) forcings. The climatic conditions prevailing during (the lead-up to) the EOT can be characterised as extremely seasonal and monsoonal, featuring a short yet intense summer period and contrasting cold winters — highly inhospitable to ice sheet growth for most of the continent, as limited snow accumulation is expected to survive the summer season. A narrow convergence zone with moist convection around the region where sub-cloud equivalent potential temperature is high is shown to exhibit a ring-like ...