Abstract. The 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 10
ocean and 4 land-surface temperature reconstructions from a range of proxy
records and compared this with a series of fully coupled, low-resolution
climate model simulations from two models (HadCM3BL and FOAM). Regional
patterns in the proxy records of temperature show that cooling across the
EOT was less at high latitudes and greater at mid-latitudes. While certain
climate model simulations show moderate–good performance at recreating the
temperature patterns shown in the data before and after the EOT, in general
the model simulations do not capture the absolute latitudinal temperature
gradient shown by the data, being too cold, particularly at high latitudes.
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 for previous research that changes in
atmospheric pCO2 are more likely to have been the driver of the EOT
climatic changes, as opposed to the opening of the Drake Passage.
Changes in the high-latitude Southern Hemisphere through the Eocene–Oligocene transition: a model–data comparison
