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  • 1 University of Hawaii Department of Oceanography 1000 Pope Road Honolulu Hawaii 96822 USA
  • | 2 Woods Hole Oceanographic Institution Department of Marine Chemistry and Geochemistry Woods Hole MA 02543 USA
  • | 3 Alfred-Wegener Institute P.O. Box 120161 D-27515 Bremerhaven Germany
  • | 4 University of British Columbia Department of Forest Sciences Vancouver BC V6T 1Z4 Canada
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Abstract  

Thorium-234 is a naturally occurring radionuclide that has been widely studied in ocean sciences. These studies use the disequilibrium between the soluble parent uranium-238 (T1/2 = 4.5·109 y), and its particle reactive daughter, 234Th (T1/2 = 24.1 d), to quantify the in-situ removal rates of 234Th on sinking particles. Here, we present additional experiments that test a new 2-l procedure in which 234Th is co-scavenged with a MnO2 precipitate. Unlike other techniques, this method can be easily applied at-sea with an overall precision and accuracy of 5%. Our experiments have sought to elucidate the effects of delaying reagent addition and precipitate filtration, differences in sample bottle types, and issues related to sample backgrounds and 234Th particulate sampling. Most of these experiments were conducted using water collected on repeated occupations of station ALOHA (22°45.0'N, 158°00.0'W), 100 km North of Oahu, Hawaii.