Pacific Proving Grounds radioisotope imprint in the Philippine Sea sediments

Highlights: • Radionuclide depth profiles were studied in sediment cores from the Philippine Sea. • ²¹⁰Pb_xs, ²²⁸Th_xs and artificial radionuclides provided the age model. • Very hight particle reactive radionulide inventories were found due to boundary scavenging. • The contribution of plutonium from the Pacific Proving Grounds is at least 60%. • Both radionuclide and bulk organic geochemistry identified a sediment layer related to 2012 typhoon Bopha. - Abstract: Radionuclide concentrations were studied in sediment cores taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial Western Pacific. High resolution deposition records of anthropogenic radionuclides were collected at this site. Excess ²¹⁰Pb together with excess ²²⁸Th and anthropogenic radionuclides provided information about accumulation rates. Concentrations of Am and Pu isotopes were detected by gamma spectrometry, alpha spectrometry and ICP-MS. The Pu ratios indicate a high portion (minimum of 60%) of Pu from the Pacific Proving Grounds (PPG). This implies that the transport of PPG derived plutonium with the Mindanao Current southward is similarly effective as the previously known transport towards the north with the Kuroshio Current. The record is compared to other studies from northwest Pacific marginal seas and Lombok basin in the Indonesian Archipelago. The sediment core top was found to contain a 6 cm thick layer dominated by terrestrial organic matter, which was interpreted as a result of the 2012 Typhoon Pablo-related fast deposition.