Pacific Ocean neodymium isotopes

MORBs. Diagrams involving neodymium isotopes show more overlap, but Indian Ocean MORBs have many e(Nd) values lower than any sample from the Pacific Ocean. 

Few systematic Sr-Nd isotope studies have been performed on ocean island xenolith suites. Ducea et al. (2002) analyzed clinopyroxenes from plagioclase-spinel and spinel peridotites from Pali, (Oahu, Hawaii) and found relatively depleted strontium and neodymium isotope systematics that they interpret as representing their evolution as residues from the extraction of Pacific Ocean crust. Consistent with this is a 61 20Ma errorchron defined by the pyroxene separates that is within error of the 80-85 Ma age of Pacific lithosphere beneath Hawaii. 

The first neodymium-isotopic analyses aimed at characterizing the oceans closely followed the initial development of neodymium isotopes as a chronometer and tracer (Richard et al., 1976 DePaolo and Wasserburg, 1976a O Nions et al., 1977). O Nions et al. (1978) was the first to report neodymium (along with lead and strontium) isotopes in manganese nodules and hydrothermal sediments. They confirmed the distinction between continental and mantle provenances of lead in hydrogenous and hydrothermal manganese sediments, respectively. Consistent with the previous studies, they found that strontium in these deposits is derived from seawater. All of the neodymium-isotope ratios in their samples from the Pacific were similar and lower than the bulk... 

The conclusion of O Nions et al. (1978) that neodymium is relatively well mixed in the oceans was soon shown to be incorrect by studies of Fe-Mn sediments (Piepgras et al., 1979 Goldstein and O Nions, 1981). These studies showed that the Pacific, Indian, and Atlantic oceans have distinct and characteristic neodymium-isotopic signatures. The North Atlantic has the lowest (old continent-like) values ( Nd = 10 to —14), the Pacific the highest (sNd = 0 to —5), and the Indian is intermediate (sNd = —7 to —10). The data, in addition, indicated some systematic geographic variability within ocean provinces. For example, the lowest values in the Atlantic were found in the far north, and some western Indian Ocean samples from locations near southern Africa had Atlantic-type values. In the Pacific, the highest values were found... 

Neodymium-isotope ratios of intermediate and deep water in the Indian Ocean are intermediate to the Atlantic and Pacific. They generally fall between s d = 1 to —9, and are consistent with domination by northward flowing circumpolar water (Bertram and Elderfield, 1993 Jeandel et al., 1998). A depth profile east of southern Africa (Figure 7) displays the same zig-zag pattern as South Atlantic intermediate and deep water, reflecting advection of NADW into the western Indian Ocean (Bertram and Elderfield, 1993). 

The broadest characteristics can be concisely summarized. Neodymium-isotope ratios in seawater vary systematically with location throughout the oceans, high in the Pacific, low in... 

Lacan E. and Jeandel C. (2001) Tracing Papua New Guinea imprint on the central Equatorial Pacific Ocean using neodymium isotopic compositions and rare earth element patterns. Earth Planet. Sci. Lett. 186(3-4), 497-512. 

Shimizu H., Tachikawa K., Masuda A., and Nozaki Y. (1994) Cerium and neodymium isotope ratios and ree patterns in seawater from the North Pacific Ocean. Geochim. Cosmochim. Acta 58(1), 323-333. 

Fig. 33. Histograms of neodymium isotopic compositions (a) compilation of all oceanic data (b-d) comparison of surface (<1 km) and deep waters (>1 km) for Atlantic, Indian, and Pacific Oceans, respectively. From Bertram...

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