Indian Ocean neodymium isotope

In terms of the global ocean, the intermediate neodymium-isotope rahos and neodymium concentrations of the circum-Antarctic/Indian oceans are not explicable through simple mixing of North Atlantic and Pacihc source waters. In the circum-Antarctic and Indian oceans, neodymium concentrations are too low (Figure 13). This is reasonable, and could be a reflection of neodymium scavenging in the water column during advective transport between the North Atlantic and circum-Antarctic on the one hand, and the Pacihc and circum-Antarctic on the other. 

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. 

Albarede F., Goldstein S. L., and Dautel D. (1997) The neodymium isotopic composition of manganese nodules from the Southern and Indian oceans, the global oceanic neodymium budget, and their bearing on deep ocean circulation. Geochim. Cosmochim. Acta 61, 1277-1291. 

Earth value (s d = —1.5 to —4.3). They concluded correctly that neodymium in the oceans is mainly derived from the continents, and incorrectly that neodymium-isotope ratios in the oceans are like strontium isotopes in the sense that they are globally well-mixed and display this restricted range. In order to reach this conclusion they ignored a sample from the Indian Ocean having high strontium-isotope ratios and a lower, even more continent-like neodymium-isotope ratio of 8n(J = —8.5. 

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). 

These observations, taken together, indicate that the neodymium-isotope ratios of intermediate and deep seawater are imprinted mainly in the Atlantic and Pacihc oceans. The circum-Antarctic is fed by both and its intermediate neodymium-isotope ratio reflects those of the Atlantic and Pacihc water sources. Indian Ocean intermediate and deep water is fed primarily by the circum-Antarctic and tends to retain a circum-Antarctic neodymium-isotope ratio. 

Passage values (Figure 7). This may indicate a source of neodymium with high isotope ratios in the South Atlantic. However, it is premature to conclude that deep South Atlantic neodymium-isotope ratios overstep the Southern Ocean values, for the following reasons. The maxima for all of the deep South Atlantic waters are between SNd = 7 to —9, more variable than presently available data from the Drake Passage but still quite similar. This range is also similar to circumpolar Fe-Mn sediments (Albare(c)de et al., 1997). Depth profiles from the western Indian Ocean near southern Africa are similar to the South Atlantic and Drake Passage, but like the South... 

Jeandel C., Thouron D., and Eieux M. (1998) Concentrations and isotopic compositions of neodymium in the eastern Indian Ocean and Indonesian straits. Geochim. Cosmochim. Acta 62(15), 2597-2607. 

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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