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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2609 |
| Date | 01 November 2005 |
| Creators | Via, Rachael Kathleen |
| Contributors | Thomas, Deborah J. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1918592 bytes, electronic, application/pdf, born digital |
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