A comparison of the quantity and composition of material caught in a neutrally buoyant versus surface-tethered sediment trap

The flux and composition of material caught using two different upper ocean sediment trap designs was compared at the Bermuda Atlantic Time-series Study site (BATS). The standard surface-tethered trap array at BATS was compared to a newly designed neutrally buoyant sediment trap (NBST). Both traps used identical cylindrical collection tubes. Of particular concern was the effect of horizontal flow on trap collection efficiency. In one experiment, mass, particulate organic carbon (POC) and particulate organic nitrogen (PON) fluxes were slightly lower (20–30%) in the NBST than in the standard BATS trap. In contrast, 234Th and fecal pellet fluxes were up to a factor of two to three lower in the NBST. In a second experiment, mass and POC fluxes decreased significantly with depth in the BATS surface-tethered trap, but not in the NBST. Different brine treatments had no measurable effect on collection efficiencies. A striking observation was that the swimmer “flux” was much larger in the standard BATS traps than in the NBST. Overall, these results show that different components of the sinking flux can be collected with differing efficiencies, depending upon how traps are deployed in the ambient environment.