Isotopic Composition of Neodymium in Waters from the Drake Passage

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Abstract
The isotopic composition of neodymium has been determined in seawaters from the Drake Passage. The Antarctic Circumpolar Current, which controls interocean mixing, flows through this passage. The parameter εNd(0) which is a function of the ratio of neodymium-143 to neodymium-144, is found to be uniform with depth at two stations with a value which is intermediate between the values for the Atlantic and the Pacific and indicates that the Antarctic Circumpolar current consists of about 70 percent Atlantic water. Cold bottom water from a site in the south central Pacific has the neodymium isotopic signature of the waters in the Drake Passage. By using a box model to describe the exchange of water between the Southern Ocean and the ocean basins to the north together with the isotopic results, an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the Pacific and the Southern Ocean. Concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth. These results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo-oceanographic studies.