Effect of the Deepening of the Tasman Gateway on the Global Ocean

1 We examine the effect of the deepening of the Tasman Seaway at the end of 2 the Eocene in a climate model with realistic late Eocene bathymetry and winds. 3 For this, we have contructed an Eocene numerical model based on the University 4 of Victoria climate model with wind forcing derived from a fully coupled Eocene 5 simulation. The model climate state is characterized by an oceanic meridional 6 overturning circulation (MOC) involving Southern Hemisphere sinking and a 7 northward atmospheric moisture transport across the equator. The deepening of 8 the Tasman Seaway in the presence of an open Drake Passage and the associ9 ated establishment of the Antarctic Circumpolar Current (ACC) have a limited 10 climatic impact on Antarctica. Nonetheless, the Antarctic deep sinking regions 11 cool sufficiently to lead to a global deep ocean cooling of 3 C. No initiation 12 of Northern Component Water is found, indicating that this may require the de13 velopment of a more mature ACC. Previous studies suggest that the Ross Sea 14 gyre cools the east coast of Australia, and expected the deepening of the Tasman 15 Seaway to lead to a warming east of Australia due to the introduction of warmer 16 water from the Australo-Antarctic Gulf. We here find that this warming is lim17 ited to close to the Australian coast, and that widespread cooling prevails further 18 off shore. 19