Abstract
On a transect between the northwest and northeast Atlantic Ocean (30°N/60°W to 60°N/2°W; June/July 1996) suspended particulate material (SPM) in 24 near-surface water samples (4 to 22 m 3 with SPM concentrations between 32 and 447 mg m −3) has been collected using a large volume centrifuge system. The samples have been analyzed for Y, the rare earth elements (REEs), and major inorganic and biogenic carrier phases such as Al (clay), Fe, Mn, POC, opal, and CaCO 3. The concentration pattern of particulate REEs roughly follows the SPM distribution. Average values (pmol l −1) are for Y (2.36), La (0.84), Ce (0.82), Pr (0.17), Nd (0.67), Sm (0.14), Eu (0.030), Gd (0.15), Tb (0.024), Dy (0.16), Ho (0.036), Er (0.12), Tm (0.018), Yb (0.13), and Lu (0.022). Extensive variability in negative Ce anomalies have been observed along our transect, with the strongest anomalies in areas of high POC abundances. Significant fractionation between LREEs and HREEs has been found for all major particulate phases. These data are characterized by (1) strong relationships ( p < 0.001) exist between concentrations of nonlithogenic (excess) HREEs (Tb–Lu) and POC values indicating that complexation with organic ligands promotes (temporary) HREE enrichment on solid surfaces. (2) The behavior of particulate Fe and Mn fractions is decoupled. While Fe and Al (clay) phases exhibit preferential uptake of LREEs (La–Gd) with crust-like signatures, particulate excess Mn is strongly coupled to the POC phase ( R 2 = 0.82) and to excess HREEs. We, therefore, suggest that the enrichment of REEs in Mn particles occurs via the formation of biogenic material (probably mediated by bacteria) and is not caused by adsorption onto Mn–oxihydroxides. Another result is that Y, in all studied relationships with the major inorganic and biogenic phases, is very similar to Ho implying their chemistries in surface ocean particulates are dominated by similar valency and ionic radii. The Y/Ho ratios (average of 69 ± 7 mol mol −1) have been very constant along our transect, and lie in between the ratios for seawater (100) and continental crust (50).
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