HR: 12:05h
AN: V11H-08    [PDF]
TI: On the 234,238U isotope systematics in two tropical estuaries: the Amazon and Fly Rivers.
AU: * Swarzenski, P W
EM: pswarzen@usgs.gov
AF: US Geological Survey, 600 4th Street South, St Petersburg, FL 33701 United States
AU: Campbell, P L
EM: psutton@usgs.gov
AF: ETI Profesionals, 600 4th Street South, St Petersburg, FL 33701 United States
AU: Porcelli, D
EM: Don.Porcelli@earth.ox.ac.u
AF: Oxford University, Dept of Earth Sciences, Oxford, OX1 3PR United Kingdom
AB: Natural concentrations of 238U and d234U were determined in estuarine surface waters of the Amazon and Fly (Papua New Guinea) Rivers to investigate U transport phenomena across river-dominated land-sea margins. On the Amazon shelf, salinity-property plots of dissolved organic carbon (DOC), pH and total suspended matter (TSM) revealed two vastly contrasting water masses that were energetically mixed. In this mixing zone, the distribution of uranium isotopes was highly non-conservative and exhibited extensive removal from the water column. Uranium removal was most pronounced within a salinity range of 0 to 16.6, and is likely the result of scavenging and flocculation reactions with inorganic (i.e., Fe/Mn oxides) and organic colloids/particles. Removal of uranium may also be closely coupled to exchange and resuspension processes at the sediment/water interface. In the Fly River estuary, 238U appears to exhibit a reasonably conservative distribution as a function of salinity. The absence of observed U removal does not necessarily imply non-reactivity, but instead may record an integration of concurrent U removal and release processes. There is not a linear correlation between d234U versus 1/238U that would imply simple two component mixing. It is likely that resuspension of bottom sediments, prolonged residence times in the lower reaches of the Fly River, and energetic particle-colloid interactions contribute to the observed estuarine U distribution. The supply of uranium discharged from humid, tropical river systems to the sea appears to be foremost influenced by particle/water interactions that are ultimately governed by the particular physiographic and hydrologic characteristics of an estuary.
DE: 4825 Geochemistry
DE: 4860 Radioactivity and radioisotopes
DE: 4885 Weathering
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting