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

Annual fluxes of particulate 230Th and 231Pa collected by sediment traps deployed at two locations in the Ross Sea are compared to expected fluxes, derived by combining the seasonal depletion of 230Th and 231Pa 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 230Th flux are greater than the flux collected by sediment traps deployed at ∼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 231Pa are slightly smaller, but comparable in magnitude to those for 230Th. 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.