Evolution of Atlantic deep-water circulation: from the greenhouse to the icehouse

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Title: Evolution of Atlantic deep-water circulation: from the greenhouse to the icehouse
Author: Via, Rachael Kathleen
Abstract: To better understand how the evolution of Cenozoic deep -water circulation related to changes in global climate and ocean basin configuration , we generated Nd isotope records from Ocean Drilling Program sites in the southeastern Atlantic to track deep water mass composition through time . We used fossil fish debris from ODP Sites 1262 -1264 (Leg 208 ) , spanning present -day water depths of 2500 -4750 m , to reconstruct the isotopic signature of deep waters over the past ~53 Ma . The data indicate an initial transition from relatively non -radiogenic values ( ? ?Nd= ~ -10 ) at 53 Ma to more radiogenic values ( ~ -8 .5 ) at ~32 Ma . From ~32 Ma to 3 .85 Ma , the Nd signal becomes more nonradiogenic , ~ -12 .3 at the top of the record . Comparison of our data with Nd isotopic records derived from a North Atlantic Fe -Mn crust show similar non -radiogenic values ( ~ -10 .5 ) in the 53 ? ?32 Ma interval and a trend toward more non -radiogenic values beginning at ~20 Ma . The data likely reflect an overall shift from a Southern Ocean deep water source to the ultimate incursion of deep waters from the North Atlantic . The non -radiogenic values at the base of the record reflect a Southern Ocean source of deep water . The shift toward more radiogenic values indicates an increased contribution of Pacific waters to the Southern Ocean source as the tectonic gateways changed after ~35 -33 Ma . The subsequent trend toward more non -radiogenic Nd isotope values is approximately concurrent with the increase of benthic foraminiferal ? ?18O values , based on comparison with a compilation of global data . Thus , changes in oceanic gateway configuration in addition to overall cooling and the build -up of continental ice on Antarctica may have altered the Nd isotope character of Southern Ocean deep waters during the early Oligocene .
URI: http : / /hdl .handle .net /1969 .1 /2609
Date: 2005-11-01

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Evolution of Atlantic deep-water circulation: from the greenhouse to the icehouse. Available electronically from http : / /hdl .handle .net /1969 .1 /2609 .

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