This activity will conduct an unambiguous (or nearly so) calibration of free-drifting cylindrical sediment traps using the in situ scavenging of 234-thorium as an independent predictor of the sinking flux. Thorium fluxes as measured by the sediment trap will be compared with predicted thorium fluxes from the in situ scavenging. To avoid historical problems with the interpretation of single thorium profiles, an expanded experiment will be performed in which both the thorium scavenging through time and the variability in space will be followed. The new profiling technique also averages the entire water column vertically, thus ensuring that any small-scale thorium minima in the profile will be quantitatively included. This set of measurements will provide the most unambiguous prediction to date of the thorium-bearing particle flux that a sediment trap is predicted to collect. If the sediment trap measured thorium flux differs greatly from the predicted value, it will be able to be concluded that the trap does not quantitatively collect the particles that are responsible for thorium transport and thus may be unlikely to be accurate for other particle classes as well. If the values agree, it can be concluded that the trap is accurate for the particles that transport thorium and thus suggest that they may be accurate for other particle classes as well. In either case, this experiment will demonstrate a robust method for the calibration of sediment trap data in the field that will be useful for other experiments on trap performance (e.g. hydrodynamics).
