Rare earth elements in suspended particulate material of North Atlantic surface waters

On a transect between the northwest and northeast Atlantic Ocean (30 degree sN/60 degreesW to 60 degreesN/2 degreesW; June/July 1996) suspended particu late 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 lar ge volume centrifuge system. The samples have been analyzed for Y, the rare earth elements (REEs), and major inorganic and biogenic carrier phases suc h as Al (clay), Fe, Mn, POC, opal, and CaCO3. 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 anomal ies in areas of high POC abundances. Significant fractionation between LREE s and HREEs has been found for all major particulate phases. These data are characterized by (1) strong relationships (p < 0.001) exist between concen trations 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 LRE Es (La-Gd) with crust-like signatures, particulate excess Mn is strongly co upled to the POC phase (R-2 = 0.82) and to excess HREEs. We, therefore, sug gest that the enrichment of REEs in Mn particles occurs via the formation o f biogenic material (probably mediated by bacteria) and is not caused by ad sorption onto Mn-oxihydroxides. Another result is that Y, in all studied re lationships with the major inorganic and biogenic phases, is very similar t o Ho implying their chemistries in surface ocean particulates are dominated by similar valency and ionic radii. The Y/Ho ratios (average of 69 +/- 7 m ol mol(-1)) have been very constant along our transect, and lie in between the ratios for seawater (100) and continental crust (50). Copyright (C) 200 1 Elsevier Science Ltd.