Fallout Pu in Annual Bands from the Coral Montastrea annularis, St. Croix, USVI

Coralline aragonite is known to incorporate certain minor or trace constituents from seawater (U, Sr, Ra, 210Pb) with essentially constant discrimination relative to Ca. Noshkin and others [Limnol. Oceanogr. 20(1975)729] reported that Pu was also incorporated with constant discrimination and suggested the use of annual bands in corals as a recording indicator of ambient seawater Pu. We report preliminary results of a study of fallout Pu in annual bands of Montastrea annularis from St. Croix, U.S.V.I. Along with fallout Pu we have determined: U, 232Th, 228Ra (as 228Th) and 210Pb (as 210Po). These determinations are used to test for constancy of element/Ca discrimination (U, 228Ra, 210Pb), to confirm the band-count chronology (228Ra, 210Pb), and as potential indicators of detrital contamination (232Th, 210Pb). Our results to date show fallout 239,240Pu in annual bands at concentrations of 90Sr deposition with a time lag of about one year; two peaks are resolved, in coral years 1959 and 1964. hence it appears that most of the available (to aragonite) Pu is rapidly removed from surface seawater. Further work is planned to elucidate the mechanism of Pu incorporation into coralline aragonite.