The Deep Western Boundary Current at the Bounty Trough, east of New Zealand: Indications for its activity already before the opening of the Tasmanian Gateway

The Eastern New Zealand Oceanic Sedimentary System is influenced by the main deep cold-water inflow to the Pacific Ocean, the Deep Western Boundary Current (DWBC). ODP Leg 181 targeted this region. The two northern sites ODP 1123 and 1124 are mainly used for interpretation of DWBC flow. Newly acquired high-resolution seismic reflection profiles directly cross ODP Site 1122 in the Outer Bounty Trough area. We can decipher the first appearance of a branch of the DWBC meandering into the Bounty Trough as early as 20 to 16.7 Ma. We identified four different drift deposits of the DWBC in the Outer Bounty Trough area. The deepest two drifts were formed before the opening of the Tasmanian Gateway and thus provide the first evidence of a pre-Oligocene deep circulation at the eastern New Zealand margin. Additionally, migration of the drift crests to the west and to the east is interpreted to indicate modifications in core flow pathway of the DWBC due to response to climate changes (Eocene cooling, cooling due to West Antarctic Ice shield build-up), tectonic influence (opening of Tasmanian Gateway) and enhanced sediment input (first turbiditic deposits of Bounty Channel).