Assessing the collection efficiency of Ross Sea sediment traps using Th-230 and Pa-231

Annual fluxes of particulate Th-230 and Pa-231 collected by sediment traps deployed at two locations in the Ross Sea are compared to expected fluxes, derived by combining the seasonal depletion of Th-230 and Pa-231 in surface waters with the steady-state production of each nuclide by radioactive decay of its respective dissolved uranium parent. Conservative (minimum) estimates of the expected Th-230 flux are greater than the flux collected by sediment traps deployed at similar to 200 m by factors of 3 and 6 at the two sites. The actual discrepancy may be much larger. The discrepancies between expected and measured fluxes of Pa-231 are slightly smaller, but comparable in magnitude to those for Th-230. The discrepancies between expected and measured fluxes for these natural radionuclides are similar in magnitude to those determined previously, using the same sediment traps, for particulate organic carbon, which suggests that the sediment traps undercollected the actual flux of sinking particles. (C) 2002 Elsevier Science Ltd. All rights reserved.