Neodymium concentration ocean

Considered separately, the neodymium-isotope ratios and the neodymium concentrations have very different implications, (i) Neodymium-isotope ratios are variable in the different oceans and within an ocean they fingerprint the advective paths of water masses. This requires that the residence time of neodymium is shorter than the ocean mixing time of 10 yr (e.g., Broecker and Peng, 1982). (ii) Neodymium concentrations appear to mimic silicate, implying orders of magnitude longer residence times of 10" yr... 

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. 

Thus, it is possible that all of the three controls are acting on the hafnium contribution to seawater. Despite the low concentrations of neodymium in seawater, the high Nd/Hf ratios in Fe-Mn crusts indicate relatively lower hafnium abundances. Because zircon is not a crystallizing phase in basalts, hafnium is not sequestered in zircon in the oceanic cmst and it may be more available for dissolution due to hydrothermal processes compared to continental rocks. As a result the flux of hafnium from the oceanic crust into seawater, relative to the continental flux, may be higher than for neodymium, making it more visible. 

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. 

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