Modelling the early Cenozoic Antarctic ice sheet oxygen isotope ratio and implications for the benthic δ18O change

At the Eocene-Oligocene Transition (~34 Ma), ephemeral ice sheets grew into a large continental-scale Antarctic ice sheet. During the late Eocene there is evidence for short-lived, continental-scale glaciations in the benthic oxygen isotope record, as well as geomorphic evidence pointing towards large-scale glaciations on Antarctica. Here, the modelled mean oxygen isotope ratio of these early Cenozoic Antarctic ice sheets is presented. Since benthic oxygen isotopes are a proxy for both the deep sea temperature and the ice volume stored on land, it is possible to estimate the benthic oxygen isotope change once the mean oxygen isotope content of the ice sheet is known.The modelled ice sheet oxygen isotope ratio of the late Eocene Antarctic ice sheets are strongly dependent on the size of the modelled continental-scale ice sheet, which in turn is determined by the bedrock. The ice sheet volume expansion during the Priabonian Oxygen Isotope Maximum (at around 37.2 Ma during the late Eocene) results in a modelled benthic oxygen isotope change between 0.3‰ and 0.55‰, sufficient to explain the observed excursions in the benthic oxygen isotope records. At the Eocene-Oligocene Transition, the modelled benthic oxygen isotope change due to ice sheet growth is found to be between 0.65‰ and 0.75‰. The remainder 0.45‰ to 0.55‰ of the observed benthic oxygen isotope change should therefore have been caused by oceanic cooling.