The removal rates of234Th and228Th from waters of the New York Bight |
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| Authors: | Aaron Kaufman Yuan-Hui Li Karl K Turekian |
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| Institution: | 1. Department of Geology and Geophysics, Yale University, New Haven, CT 06520, U.S.A.;2. Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY 10964, U.S.A. |
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| Abstract: | The mean residence time (τ) of thorium with respect to non-radioactive removal from water was determined as a function of location in three traverses of the New York Bight using both234Th/238U and228Th/228Ra. τ correlates well with salinity increasing from about ten days near shore to 70 days at the shelf break. It shows a much weaker correlation with suspended matter concentrations both because suspended matter varies in its scavenging efficiency and because salinity is a longer-term integrator of scavenging potential.τ's computed from228Th/228Ra were often higher than those computed from234Th/238U either because of the detrital matter present as reflected in the232Th concentrations or because the water parcels had recently arrived from environments of lower scavenging efficiency.Anomalous isotopic concentrations found in three adjacent samples can best be explained as the result of an episodic release of228Ra from bottom sediments at a rate 200 times the normal one. |
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