HR: 08:00h
AN: PP51F-01 INVITED     [Abstracts]
TI: New insights into Atlantic sector paleoceanography from Nd isotopes
AU: * Scher, H D
EM: howie@earth.rochester.edu
AF: University of Florida, Department of Geological Sciences 241 Williamson Hall P.O. Box 112120, Gainesville, FL 32611 United States
AU: Martin, E E
EM: emartin@geology.ufl.edu
AF: University of Florida, Department of Geological Sciences 241 Williamson Hall P.O. Box 112120, Gainesville, FL 32611 United States
AB: High-resolution (<300 kyr) Nd isotope records from the middle Eocene to early Miocene have been generated from three locations in the Atlantic sector of the Southern Ocean. Variability of ε_Nd values in deep waters on Agulhas Ridge (Site 1090) and Maud Rise (Sites 689 and 690) reflect water mass mixing, which responded to Southern Ocean gateways, cryospheric development, and oceanographic change. ε_Nd gradients between horizontally and vertically offset sites in these oceanographic provinces evolved in response to changes in circulation. The least radiogenic ε_Nd values at all sites occur during the early middle Eocene. Late middle Eocene ε_Nd values are distinct from early middle Eocene values at all sites because of a prominent shift toward higher values around 41 Ma. Within the uncertainty of age models and sampling resolution, the shift occurs at the same time at all sites and is best explained by the initial opening of Drake Passage, which allowed radiogenic Pacific seawater to mix into the Atlantic sector. This interpretation implies that opening of the Tasmanian Gateway removed the final barrier to a complete circum-Antarctic pathway. ε_Nd values on Agulhas Ridge become much more radiogenic than on Maud Rise during the late Eocene, suggesting multiple deep water production areas in the Southern Ocean. Deep-water cooling and organic carbon burial are associated with the change in circulation that accompanied the opening of Drake Passage. During the Oligocene all ε_Nd values become less radiogenic. At Maud Rise a vertical ε_Nd gradient is established as Site 690 ε_Nd values becomes less radiogenic than Site 689. Despite the offset, Sites 689 and 690 experience parallel long-term secular variability during the Oligocene. Initially, ε_Nd values at Agulhas Ridge are more radiogenic than Maud Rise; however, this gradient decreases during the Oligocene until the values at Sites 1090 and 689 become statistically indistinguishable in the early Miocene. Steadily decreasing ε_Nd values at Agulhas Ridge during the Oligocene and Miocene are believed to reflect the increasing influence of nonradiogenic deep waters sourced from the North Atlantic.
DE: 1040 Radiogenic isotope geochemistry
DE: 1621 Cryospheric change (0776)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005