First study on236U in the Northeast Pacific Ocean using a new target preparation procedure for AMS measurements.
We succeeded in obtaining the depth profile of236U for a sampling station in the Northeast Pacific Ocean using only one litre of seawater sample from each depth. For this purpose, a new procedure was developed that allowed for the preparation of accelerator mass spectrometry targets for trace uranium using only 100 μg of iron carrier material. The236U concentrations in water samples from the Northeast Pacific Ocean showed large variations from (9.26 ± 0.42) × 106atoms/kg at 60 m depth to (0.08 ± 0.02) × 106atoms/kg at a depth of 3000 m. The high236U concentrations in surface water reflect the input of236U by global and local fallout from nuclear weapons tests. The low236U concentrations in seawater from 1500 m and below are an indicator for the low vertical diffusion of surface water to deeper layers in the North Pacific Ocean. The total inventory of236U on the water column was (8.35 ± 0.23) × 1012atoms/m2, which is lower compared to those of other ocean regions solely affected by global fallout on comparable latitudes. This study represents the first dataset for236U in the Pacific Ocean and shows the possibility of downsizing sample volumes which may help in future applications of236U as tracer for large ocean areas.
Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526, Japan. Electronic address: rosmarie_eigl@yahoo.de.
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R
Eigl
VERA-Laboratory, Faculty of Physics - Isotope Research, University of Vienna, Währinger Str. 17, 1090, Vienna, Austria.
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Steier
VERA-Laboratory, Faculty of Physics - Isotope Research, University of Vienna, Währinger Str. 17, 1090, Vienna, Austria; iThembaLABS (Gauteng), National Research Foundation, Private Bag 11, WITS 2050, Johannesburg, South Africa.
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Winkler
Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526, Japan.
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Sakata
Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577, Japan.
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Sakaguchi
D013058:Mass Spectrometry; D010140:Pacific Ocean; D011834:Radiation Monitoring / Q000379:methods*; D011847:Radioactive Fallout / Q000032:analysis; D014501:Uranium / Q000032:analysis*
D011847:Radioactive Fallout; D014501:Uranium
Accelerator mass spectrometry; Geotraces; Global fallout; Pacific Ocean; U-236