A 12 Million Year Record of Caribbean Outflow to the Northwest Atlantic Based on Radiogenic Nd Isotopes Obtained from ODP Site 1006.

Kirillova, Valeriia (2013) A 12 Million Year Record of Caribbean Outflow to the Northwest Atlantic Based on Radiogenic Nd Isotopes Obtained from ODP Site 1006. (Master thesis), Saint Petersburg State University ; University of Hamburg, Saint Petersburg, Russia ; Hamburg, 66 pp.

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Abstract

The closure of the Central American Seaway (CAS) has been an interesting research problem for several decades. The exact timing of Panama seaway closure is still unknown, though many methods have been used to try and solve this scientific problem. One such method uses the neodymium isotopic composition (Nd IC) of authigenic Fe-Mn oxihydroxides, which has been successfully applied as a paleoceanographic tool for water mass tracing due to the residence time of Nd in the oceans being shorter than the ocean overturning time and due to independence of Nd IC from biological fractionation and physical processes.
The aim of our project was to reconstruct the paleocirculation in the Florida Straits for the last 12 Myrs, and to consider the results in connection with either the Panama closure or the Northern Hemisphere Glaciation. For this purpose we carried out isotopic measurements of Nd, Sr and Pb on the sediment core from ODP Site 1006 (water depth 658 m).
The methods applied included the leaching of sediments to obtain the authigenic water signal from Fe-Mn oxyhydroxides and total dissolution to obtain the detrital fraction composition. Measurements were made at GEOMAR Helmholtz Centre for Ocean Research, Kiel, using an Inductive-Coupled Plasma Mass Spectrometer (ICP-MS). Pb IC results were obtained only for the detrital material since the concentrations of Pb in the leachate samples were too low for the isotopic measurements. Isotopic compositions in several core-top sediments were also measured, which could tell us if our signal was a true seawater one.
The εNd curves obtained for authigenic and detrital material almost replicate each other. However we observed a strong correlation of our Nd IC record for leachates with other records for Sites close to our. This is why we suggest that we can trust our age model and consider our seawater signal as not having been contaminated by the detrital fraction. According to the Nd IC curve, most likely the Panama seaway was closed by 9.5 Ma for intermediate water exchange, but the final closure timing is hard to evaluate. It has also been shown that an intensive boundary exchange with the material from the continents plays an important role in deriving isotopic signals (since the Site is so shallow and close to the ocean margin). Core top Nd IC was different depending on whether carbonate was removed prior to leaching or not. Therefore as possible future work we would suggest to constrain measurements of Nd IC using fossil fish teeth, as they should reflect a true bottom water signal. Direct seawater measurements in this location would also be very helpful.

Document Type: Thesis (Master thesis)
Thesis Advisors: Frank, Martin, Osborne, Anne H. and Krylov, Alexey
Keywords: Central American Seaway, CAS; Panama Canal; Neodymium isotopic composition; Paleoceanography; Florida Strait; Paleocirculation; Northern hemisphere glaciation
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Open Access Journal?: No
Projects: POMOR
Expeditions/Models/Experiments:
  • ODP Site 1006
Date Deposited: 21 Jan 2014 07:05
Last Modified: 04 Mar 2015 10:29
URI: http://oceanrep.geomar.de/id/eprint/23152

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