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Influence of the Mediterranean Outflow on the isotopic composition of neodymium in waters of the North Atlantic

Piepgras, D. J. and Wasserburg, G. J. (1983) Influence of the Mediterranean Outflow on the isotopic composition of neodymium in waters of the North Atlantic. Journal of Geophysical Research C, 88 (C10). pp. 5997-6006. ISSN 0148-0227. doi:10.1029/JC088iC10p05997.

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The isotopic composition of neodymium in the water column of the eastern North Atlantic near the Strait of Gibraltar has been determined for several depths. The data show that the Mediterranean outflow results in a significant shift in ε_(Nd)(0) toward more radiogenic values of ^(143)Nd/^(144)Nd in the water column at a 1000-m depth. This corresponds to a depth in the neighborhood of the salinity maximum associated with the Mediterranean outflow. The core of the Mediterranean outflow gives ε_(Nd)(0) = −9.8, as compared to ε_(Nd)(0) ≈ −12 in overlying and underlying waters, demonstrating that the Mediterranean waters are distinct from the Atlantic. From mixing considerations we estimate that pure Mediterranean waters have ε_(Nd)(0) ≈ −6. Possible sources of this relatively radiogenic Nd could be from drainage of young continental terranes or the injection of remobilized Nd from deep-sea sediments that have a young radiogenic volcanic component. New data from a depth profile in the western Atlantic is presented. Comparison of Nd data for the eastern North Atlantic with that for the western North Atlantic shows fundamental differences in the water column structures for ε_(Nd)(0). While both regions show a pronounced maximum in ε_(Nd)(0), the western basin maximum occurs at the near surface rather than at 1000 m. In addition, deep waters of the eastern basin are found to be more radiogenic than the western basin. These differences indicate several sources of isotopically distinct Nd in the North Atlantic. The deep waters of the North Atlantic (>1000 m) have the lowest values of ε_(Nd)(0) measured in the oceans. We believe that the source of these low ε_(Nd)(0) values, which we associate with North Atlantic deep water, is either from freshwater drainage off the Precambrian shields of North America and Asia into the Arctic Ocean or from the injection of ‘older,’ continentally derived REE from deep-sea sediments. Sm and Nd concentrations are found to increase with depth and ε_(Nd)(0) changes with depth, indicating both vertical and lateral transport processes from different sources. This suggests a surface source of Nd and injection of REE into the water column from deep-sea sediments or large-scale bottom currents with high REE concentrations.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1983 by the American Geophysical Union Received September 20, 1982; revised March 14, 1983; accepted March 15, 1983. We thank C. Wunsch and M. S. McCartney for providing ship time in the Atlantic. We appreciate the cooperation of the crew of the RV Atlantis II during the collection of the samples. B. Lowman and J. Jennings performed the nutrient analyses. This study has benefited greatly from many discussions with M. Stordal. We would also like to thank T. Takahashi and C. G. H. Rooth for their suggestions on improving the manuscript. This research was supported by grant NSF OCE-8108595. Basic laboratory operations were supported by NASA NGL-05-002-188. This is contribution 3803 (425) of the Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences3803
Lunatic Asylum Lab425
Issue or Number:C10
Record Number:CaltechAUTHORS:20131016-091716372
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Official Citation:Piepgras, D. J., and G. J. Wasserburg (1983), Influence of the Mediterranean Outflow on the isotopic composition of neodymium in waters of the North Atlantic, J. Geophys. Res., 88(C10), 5997–6006, doi:10.1029/JC088iC10p05997
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41939
Deposited By: Tony Diaz
Deposited On:16 Oct 2013 17:53
Last Modified:10 Nov 2021 04:36

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