Uranium, Pb-210, Ra-228, and Pu-239,240 were determined in annual bands (1954-1974) from M. annularis collected off Broward County, FL. These data extend earlier work on St. Croix M. annularis (EOS 52, 1031) to determine whether annual bands preserve a history of fallout Pu in surface seawater.

Published data suggest that corals incorporate U, Pb-210 and Ra from seawater with constant discrimination relative to Ca. With one exception, annual bands from this specimen have a constant U/Ca ratio which is indistinguishable from the seawater ratio. Pb-210 and Ra-228 data are more variable. This is probably due either to variable concentration of these nuclides in ambient seawater or to variable discrimination during incorporation; assuming constant seawater concentrations and annual banding, discrimination was constant to within 14% for Pb-210 and 16% for Ra-228.

The fallout Pu records in the Broward County and St. Croix M. annularis are similar, showing major peaks in annual bands for 1959 and 1964. Peak magnitudes are closely similar for 1964, but Broward County shows a stronger maximum in 1959. The coral Pu records generally mimic records of atmospheric deposition of Sr-90 and coral Pu, and peak broadening in the coral records are compatible with a mean residence time of 2-4 years for the bulk of the fallout Pu in surface seawater.