Ocean particle chemistry: The fractionation of rare earth elements between suspended particles and seawater

Journal Article · Tue Mar 01 00:00:00 EST 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90559-2· OSTI ID:7182962

Sholkovitz, E R ^[1]; Landing, W M; Lewis, B L ^[2]

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1. Woods Hole Oceanographic Institution, Woods Hole, MA (United States)
2. Florida State Univ., Tallahassee, FL (United States)

Sargasso Sea suspended particles were sequentially digested with three chemical treatments (acetic acid, mild HCl/HNO[sub 3], and HF/HNO[sub 3]/HCl in a bomb). The latter two treatments dissolve detrital minerals, while the acetic acid removes surface coatings (organic matter and Mn oxides). The rare earth element (REE) composition of the surface coatings, in marked contrast to the crust-like REE composition of the two detrital phases, is extensively fractionated with respect to both filtered seawater and the crust. Surface coatings are responsible for the removal and fractionation of REEs from seawater and, as such, play a key role in the marine geochemical cycles of trace elements. Relative to seawater, the surface coatings are systematically enriched tenfold across the trivalent REEs from Lu to La and develop large positive Ce-anomalies. The Ce-anomalies of the coatings switch from being negative (seawater-like) in the upper 100 m to being strongly positive at greater depths. The ingrowth of Ce and LREEs on particle surfaces reflects the in situ oxidation of dissolved Ce(III) to particulate Ce(IV), and the preferential removal of LREE(III)s over HREE(III)s. REEs(III) fractionation of this type is consistent with particle/solution models. Both processes appear to be related to the in situ formation of Mn oxide particles from the oxidation of dissolved Mn(II) in the upper 200 m of the water column. Preferential removal of LREEs in the upper waters is countered by their preferential release at depth due to remineralization of surface coatings on particles. A new method is explored for estimating the residence time of suspended particles by combining Ce concentration data of dissolved and surface-bound phases with the Ce(III) oxidation rate measurements of MOFFETT (1990). A Ce-based residence time of thirteen days is similar in magnitude to the value calculated from U-[sup 234]Th disequilibria in the Sargasso Sea.

• OSTI ID: 7182962
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 58:6; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
PARTICLES
CHEMICAL REACTIONS
RARE EARTHS
PARTITION
SEAS
WATER CHEMISTRY
CERIUM
HYDROCHLORIC ACID
HYDROFLUORIC ACID
MANGANESE OXIDES
CHALCOGENIDES
CHEMISTRY
CHLORINE COMPOUNDS
ELEMENTS
FLUORINE COMPOUNDS
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
MANGANESE COMPOUNDS
METALS
OXIDES
OXYGEN COMPOUNDS
SURFACE WATERS
TRANSITION ELEMENT COMPOUNDS
540320* - Environment
Aquatic- Chemicals Monitoring & Transport- (1990-)