Abstract:
The opening of the Drake and Tasman passages initiated proto-Antarctic Circumpolar Current (ACC) flow during the late Eocene to early Oligocene, which contributed to the isolation and glaciation of Antarctica and greatly impacted global thermohaline circulation. Even at its early stages of development, the proto-ACC hindered the Weddell Sea surface waters from mixing with warm equatorial surface waters of the subtropical gyre. The isolated Weddell Sea surface waters then cooled and became a source of the cold, dense Southern Component Water (SCW) that flowed north as a deepwater mass from Antarctica. We present new benthic foraminiferal delta (super 18) O and delta (super 13) C records from the Walvis Ridge, ODP Site 1263, with comparisons to published records from other ocean basins in the late middle Eocene to early Oligocene (40-33 Ma). Comparison of Site 1263 to Site 689 on the Maud Rise reveals the paleocirculation history of the SCW and its effect at the Walvis Ridge. The delta (super 18) O record from Site 1263 correlates to equatorial Pacific Site 1218 and Site 689 from 40 to approximately 38.5Ma. At 38.5Ma, the Weddell Sea deepwater continued to cool, while deep water at the Walvis Ridge and Site 1218 was warmer until 37.5Ma. At this time, the Site 1263 delta (super 18) O diverged from Site 1218 and began to cool and track Site 689 through 33Ma. The correlation between these records shows that SCW was the primary deepwater mass at the Walvis Ridge after 37.5Ma, while more northern locations (e.g., Site 1218, North Atlantic Site 1053) maintained warmer deepwater as indicated by their published delta (super 18) O records. This implies that the early stages of the development of the Drake Passage and proto-ACC impacted South Atlantic deepwater circulation in the late middle to late Eocene, prior to the large isotopic shift of the early Oligocene associated with continent-scale Antarctic glaciation and the deepening of the Tasman Gateway.