Dataset: sediment trap PN flux
Deployment: AT15-61

Sinking particulate nitrogen (PNsink) mass and d15N analysis: Sinking particulate material was collected using surface-tethered floating particle-interceptor traps (PIT) equipped with 12 polycarbonate cylinders, deployed for up to 70 hours. Floating sediment traps were deployed at 200 m at Stations 3 and 5 on the 2010 cruise; for all other stations, traps were deployed at 100 m. Sediment trap samples were collected into a brine solution and then filtered and split into replicate samples. In most cases, two splits were collected from each sediment trap, one of which was acidified to remove inorganic carbon. In 2010 filtration removed the contribution of “swimmers” from sediment trap material. On the 2011 cruise, “swimmers” were identified by dissecting microscopy and hand-picked from sediment trap samples using sterilized micropipettors and forceps to remove their isotopic contribution to the sinking flux. Mass and isotopic fluxes were determined by dividing the mass of sinking particulate material captured in each trap by the trap surface area and by the duration (hrs) of trap deployment. Subsequently, the total mass flux was multiplied by the %N determined by combustion analysis of trap samples at the UC Davis Stable Isotope Facility to calculate PNsink mass fluxes; the d15N of trap samples was determined at the same time. The limit of detection for combustion analysis is 1.5 µmols N and the precision of the d15N measurement is + 0.3‰. No systematic difference was observed in the d15N of acidified vs. non-acidified trap samples.

References:

Soutar, A., Kling, S. A., Crill, P. A. & Duffrin, E. MONITORING MARINE-ENVIRONMENT THROUGH SEDIMENTATION. Nature 266, 136-139, doi:10.1038/266136a0 (1977).

Knauer, G. A., Martin, J. H. & Bruland, K. W. Fluxes of particulate carbon, nitrogen, and phosphorus in the upper water column of the northeast Pacific. Deep-Sea Research 26, 97-108, doi:10.1016/0198-0149(79)90089-X (1979).