Supplementary material to "Changes in the high latitude Southern Hemisphere through the Eocene-Oligocene Transition: a model-data comparison"

Abstract

Global and regional climate changed dramatically with the expansion of the Antarctic Ice sheet at the Eocene-Oligocene Transition (EOT). These large-scale changes are generally linked to declining atmospheric pCO2 levels and/or changes in Southern Ocean gateways such as the Drake Passage around this time. To better understand the Southern Hemisphere regional climatic changes and the impact of glaciation on the Earth's oceans and atmosphere at the EOT, we compiled a database of sea and land surface temperature reconstructions from a range of proxy records and compared this with a series of fully-coupled climate model simulations. Regional patterns in the proxy records of temperature show that cooling across the EOT was less at high latitudes and greater at mid-latitudes. Climate model simulations have some issues in capturing the zonal mean latitudinal temperature profiles shown by the proxy data, but certain simulations do show moderate-good performance at recreating the temperature patterns shown in the data. When taking into account the absolute temperature before and after the EOT, as well as the change in temperature across it, simulations with a closed Drake Passage before and after the EOT or with an opening of the Drake Passage across the EOT perform poorly, whereas simulations with a drop in atmospheric pCO2 in combination with ice growth generally perform better. This provides further support to previous research that changes in atmospheric pCO2 are more likely to have been the driver of the EOT climatic changes, as opposed to opening of the Drake Passage.