Near the Eocene's close (∼34 million years ago), the climate system underwent one of the largest shifts in Earth's history: Antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed. Previous studies conjectured that poleward penetration of warm, subtropical currents, the East Australian Current (EAC) in particular, caused Eocene Antarctic warmth. Late Eocene opening of an ocean gateway between Australia and Antarctica was conjectured to have disrupted the EAC, cooled Antarctica, and allowed ice sheets to develop. Here we reconstruct Eocene paleoceanographic circulation in the Tasmanian region, using (1) biogeographical distributions of phytoplankton, including data from recently drilled Ocean Drilling Program Leg 189 sites and (2) fully coupled climate model simulations. We find that the EAC did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern. Our results do not support changes in “thermal isolation” as the primary driver of the Eocene-Oligocene climatic transition.


Originally published by AGU Publications, in Paleoceanography. DOI: 10.1029/2004PA001014

Manuscript received: 28 July 2004

Manuscript accepted: 4 October 2004

Version of record online: 18 December 2004


Climate dynamics, Meteorology and Atmospheric Dynamics: Paleoclimatology, Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions, Paleoceanography

Date of this Version