Deciphering anthropogenic uranium sources in the equatorial northwest Pacific margin

This work reports the first high-resolution deposition records of anthropogenic uranium(U-236 and U-233) in a sediment core taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial northwest Pacific Ocean. Two notable peakswere observed in both profiles of U-236 and U-233 concentrations, with a narrower peak in 1951-1957 corresponding to close-in Pacific Proving Grounds (PPG) signal, and a broader peak in 1960s-1980s corresponding to the global fallout fromnuclear weapons testing. U-236 and U-233 areal cumulative inventories in the studied sediment core are (2.79 +/- 0.20).10(12) atom.m(-2) and (3.12 +/- 0.41).10(10) atom.m(-2), respectively, about 20-30% of reported U-233 and U-236 inventories from the direct global fallout deposition. The overall U-233/U-236 atomic ratios obtained in this work vary within (0.3-3.5).10(-2), with an integrated U-233/U-236 atomic ratio of (1.12 +/- 0.17).10(-2). The contribution from global fallout and close-in PPG fallout to U-236 in the sediment core is estimated to be about 69% and 31%, respectively. We believe the main driving process for anthropogenic uranium deposition in the Philippine sediment is continuous scavenging of dissolved U-236 from the surface seawater by sinking particles. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

This study presents the first high-resolution deposition records of anthropogenic uranium (U-236 and U-233) in a sediment core taken at the Philippine Sea continental slope off Mindanao Island in the equatorial northwest Pacific Ocean. The results show two notable peaks in U-236 and U-233 concentrations, with one peak corresponding to close-in Pacific Proving Grounds signal and the other peak corresponding to global fallout from nuclear weapons testing.