Uranium and thorium decay series nuclides in plankton from the Caribbean1

Zooplankton (predominantly calanoids and cyclopoids) from the Caribbean were analyzed for 238 U, 234 U, 232 Th, 228 Th, 228 Ra, 2 2 6 Ra, 210 Pb, and 210 Po. The concentration factor in the zooplankton relative to seawater is highest for 210 Po. 210 Pb and 228 Th have similar concentration factors and are comparable (when normalized to 226 Ra) to reported fiber‐scavenging experimental data on 210 Pb and 234 Th. The dominant transport agent for 210 Po and 210 Pb from the mixed layer to depth cannot be unmodified zooplankton debris.