Free floating, unpoisoned surface tethered sediment traps were used to quantify fluxes of sinking particles at St P2 (16.5ºN 107ºW) in January 2017, deployed from the R/V Sikuliaq on cruise SKQ201617S. Trap depths ranged between 69 m and 965 m, and trap deployments ranged between 21 and 91 hours with deeper traps deployed for longer. Traps were deployed in arrays of two traps per line. Two types of traps were deployed: 1) in shallow waters (<150 m), traps with a solid plastic cone top (0.46 m2 opening area) were used, 2) in deep waters (>150 m), net traps (1.24 m2 opening area) modeled from (Peterson et al., 2005) were used. For both types of trap, the cod end had bottoms that were open during deployment and during an 8 hour equilibration period at the target depth performed to remove oxygen contamination. Cod ends were closed with a gate valve, using a pre-programmed electronic dissolving link (burn wire) system controlled by an onboard Arduino microcontroller to start collection at the correct depth, and a second gate valve that closed the top of the cod end before retrieval. The aspect ratio, or height/trap mouth diameter, of the net traps was 2.5 while the aspect ratio of the cone traps was 0.6. These two types of traps have been shown to collect material with similar efficiency when normalized by opening area (Cram et al., 2022). No salt solution was used with these traps and no poisons were used in any chamber.
Some trap deployments functioned as simple sediment traps, and some deployments were combined trap and in situ incubators. The combined trap incubators consisted of upper and lower chambers. The material used to calculate fluxes reported here was collected from the upper chamber and was not incubated. Sinking material was collected in the lower incubation chamber, then isolated by closed a gate valve and injected with 15N-NO2- . While the incubation occurred (in situ), sinking material was collected in an upper chamber that never encountered the spiked material. However, we do not report d15N natural stable isotopes for the sediment trap material here due to proximity to the incubation.
After every deployment, sediment trap material was filtered onto pre-combusted GF-75 filters (0.3 µm nominal pore size). To conform to community standards, zooplankton carcasses were not included in the measurements of carbon and nitrogen flux. Filter samples (particles only) were wafted with HCl overnight to remove carbonate, dried at 40°C, packed into silver foil cups, and sent to the University of Washington Isolab facility in the Department of Earth and Space Sciences (Seattle, WA) for C and N analysis utilizing an Costech elemental analyzer attached to an isotope ratio mass spectrometer (ThermoFinnegan MAT 253).
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