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

• Published in: Journal of Geophysical Research
• Main Authors: Piepgras, D. J., Wasserburg, G. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 1983
• Subjects: Arctic; Arctic Ocean; Western Basin; North Atlantic Deep Water; North Atlantic
• Online Access: https://authors.library.caltech.edu/41939/; https://authors.library.caltech.edu/41939/1/jgrc3075.pdf; https://resolver.caltech.edu/CaltechAUTHORS:20131016-091716372

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.