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Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations

Piepgras, D. J. and Wasserburg, G. J. (1987) Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations. Geochimica et Cosmochimica Acta, 51 (5). pp. 1257-1271. ISSN 0016-7037.

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The isotopic composition of Nd in the water column from several western North Atlantic sites and formational areas for North Atlantic Deep Water shows extensive vertical structure at all locations. In regions where a thermocline is well-developed, large isotopic shifts (2 to 3 ϵ units) are observed across the base of the thermocline. Regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth. In general, the data reveal an excellent correlation between the Nd isotopic distribution in the western North Atlantic water column and the distribution of water masses identified from temperature and salinity characteristics. NADW, as identified from T-S properties, is also characterized by a well-defined isotopic composition having ϵ_(Nd)(0) = −13.5 ± 0.5. This signature is associated with waters identified as NADW from high latitudes near formational areas in the Labrador Sea down to the equatorial region. The isotopic signature of NADW would appear to be formed by a blend of more negative waters originating in the Labrador Sea (ϵ_(Nd)(0) < −18) and more positive waters originating in the overflows from the Norwegian and Greenland Seas (ϵ_(Nd)(0) ≈ −8 to −10) and is consistent with classical theories on the formation of NADW. The isotopic signature of NADW is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic Nd associated with northward-spreading Antarctic Intermediate and Bottom Waters. The preservation of the isotopic signature of NADW over these large distances indicate that the REE undergo extensive lateral transport. The isotopic composition of Nd is largely conservative over the time scales of mixing within the Atlantic in spite of the intrinsic nonconservative behavior of neodymium. Nd concentration gradients generally show surface waters to be depleted in Nd relative to deep waters, which must require vertical transport processes. However, isotopic differences in the water column preclude the local downward transport of REE from the surface into underlying deep waters as a simple explanation of the concentration gradient. The apparent decoupling of REE in NADW from overlying (local) surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1987 Pergamon Journals Ltd. Received May 5, 1986; accepted in revised form February 13, 1987. We wish to thank J. Sarmiento and I. Takahashi for allowing us to participate in the TTO/TAS expedition. We also wish to thank the PACODF crew for making the hydrographic measurements on the samples collected during this cruise. T. Takahashi also kindly provided us with the TTO/NAS samples. C. Wunsch provided us with ship time and on-board hydrographic measurements for samples collected from cruise A-II 109-1. J. Lazier provided the ship time for the Labrador Sea work. Nutrient analyses on these samples were kindly measured by P. Jones at the Bedford Institute of Oceanography. Finally, we wish to thank the crews of the RV Atlantis II, RV Knorr and the CSS Hudson for their support during the collection of these samples. We are grateful to M. P. Bacon for his review, the associate editor for his comments and H. De Baar for his criticisms. Their comments helped to improve this report. This work was supported in part by grants from the National Science Foundation (NSF OCE 8308884 and NSF OCE 8320516) and the National Aeronautics and Space Administration (NAG 9-43). Division Contribution No. 4118 (491). Editorial handling: H. Elderfield
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NSFOCE 8308884
NSFOCE 8320516
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Caltech Division of Geological and Planetary Sciences4118
Lunatic Asylum Lab491
Issue or Number:5
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Official Citation:D.J Piepgras, G.J Wasserburg, Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations, Geochimica et Cosmochimica Acta, Volume 51, Issue 5, May 1987, Pages 1257-1271, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42123
Deposited By: Ruth Sustaita
Deposited On:30 Oct 2013 16:56
Last Modified:09 Mar 2020 13:19

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