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Paper No. 105-13
Presentation Time: 8:00 AM-5:30 PM
OPENING OF THE TASMAN GATEWAY AND THE CONSEQUENCES FOR OCEAN CIRCULATION IN THE PALEOGENE
The modern-day Antarctic Circumpolar Current (ACC) plays an important role in controlling climate and productivity around the globe, however, the origins and mechanisms driving the onset of this current remain poorly understood. The tectonic opening of ocean gateways during the Eocene break-up of Gondwana has been suggested to have initiated a circum-Antarctic current. Further, the changes in ocean circulation around this time have been thought to provide suitable conditions for Antarctic glaciation. These ideas have been debated for decades through various modelling and proxy studies. Recently, high resolution modelling has provided more support to the importance of these ocean gateways in influencing currents and climate in Antarctica. The South Tasman Rise (STR) was likely the final barrier to an open ocean for the ACC, situated in the middle of the Tasman Gateway, between East Antarctica and Australia. Timing of the subsidence of the STR is a key, but elusive, piece of information regarding the opening of the Tasman Gateway and tectonic initiation of the ACC. Geochemical analysis of marine sediment core DSDP site 281, located on the STR, has revealed new information about the timing and environmental conditions surrounding the subsidence of the STR. A new age model has been created using strontium isotope stratigraphy. Rare earth element patterns and neodymium isotopes provide an insight into environmental conditions and ocean circulation. These results show a shallow, restricted circulation environment with initial deepening prior to 35 Ma, an increasingly well-ventilated ocean across the Eocene-Oligocene transition, and a long hiatus followed by an open water depositional environment at 22 Ma. These data provide new constraints on the opening of the Tasman Gateway, indicating that the gateway was open sufficiently to allow a proto-ACC to circulate before the Eocene-Oligocene transition and the start of glaciation in Antarctica.