The geochemistry of rare earth elements in the Amazon River estuary
- Woods Hole Oceanographic Institution, MA (United States)
The estuarine geochemistry of rare earth elements (REEs) was studied using samples collected in the Amazon River estuary from the AmasSeds (Amazon Shelf SEDiment Study) cruise of August 1989. Extensive removal of dissolved (0.22 [mu]m filtered) trivalent REEs from river water occurs in the low (0--6) salinity region. Removal by the salt-induced coagulation of river colloids leads to fractionation among the REE(III) series; the order of removal is light REEs > middle REEs > heavy REEs. There also is the enhanced removal of Ce (relative to trivalent La and Nd) in the low salinity (0--6) zone and in the zone of high biological activity. This is the first field observation of strong Ce removal associated with coagulation of river colloids and biological productivity. The argument is made that the decrease in the Ce anomaly across a biological front is caused by biologically mediated oxidation of Ce(III) to Ce(IV). Coagulation of river colloids and biologically mediated oxidation of Ce(III) lead to fractionation of REE(III) and redox modification of Ce. These processes result in the REE composition becoming fractionated relative to the Amazon River water and crust and more evolved toward the REE composition of the oceans. This study implies that reactions in estuaries play significant, yet poorly understood roles in controlling the REE composition and Ce anomaly of the oceans. 46 refs., 9 figs., 2 tabs.
- OSTI ID:
- 6084681
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 57:10; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
540320* -- Environment
Aquatic-- Chemicals Monitoring & Transport-- (1990-)
AMAZON RIVER
CERIUM
CHEMISTRY
ELEMENTS
ENVIRONMENTAL TRANSPORT
ESTUARIES
FRACTIONATION
GEOCHEMISTRY
LANTHANUM
MASS TRANSFER
METALS
NEODYMIUM
RARE EARTHS
REMOVAL
RIVERS
SEPARATION PROCESSES
STREAMS
SURFACE WATERS