The isotopic composition of neodymium in the North Pacific

Abstract

We have determined the isotopic composition of neodymium in two water column profiles in the western North Pacific and in bottom waters from three other locations in the North Pacific. The vertical profiles reveal that the water column is stratified with respect to isotopic composition. Mid-depths associated with Pacific Deep Water are uniform having ϵ Nd (0) ≈−3. Shallow waters are variable, but deep waters are less radiogenic having ϵ Md (0) = −4.4 to −5 in the western basin. The more negative bottom waters in the western North Pacific provide evidence for the advective transport of rare earth elements from Antarctic sources to this region. Bottom waters in the eastern North Pacific are more radiogenic ( ϵ Nd (0) = −3.3 to −3.8) indicating very little transport of REE from Antarctic sources to this basin. Overall, the isotopic composition of Nd in Pacific bottom waters appears to be conservative when compared to the silica distribution in spite of evidence for Nd removal. The findings are generally compatible with other parameters such as temperature, salinity and nutrient distributions. The presence of Nd isotopic signatures associated with Antarctic sources in these waters provides evidence for a small component of rare earth elements of North Atlantic origin in the bottom waters of the North Pacific. This is the first tracer evidence to corroborate the suggestion of Reid and Lynn (1971) that some of the temperature and salinity properties of the deep waters of the North Pacific originated in the Norwegian and Greenland Seas.