[In situ N2 production rates from the ETNP ODZ] - In situ N2 production rates from the Eastern Tropical North Pacific Oxygen Deficient Zone on the R/V Sikuliaq cruise SKQ201617S in January 2017 and R/V Revelle in April 2018 cruise RR1805 (Dimensions: Diversity, assembly and function of microbial communities on suspended and sinking particles in a marine Oxygen Deficient Zone)

For all 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 incubation and closed a bottle containing only seawater. 15N labeled nitrite was added in situ to both the +particles chamber and the water only chamber using a syringe and the Arduino microcontroller.

Incubations were 12-36 hours. Immediately after returning the sediment trap-in situ incubator systems shipboard, the experimental chambers were sampled using single-use needles into 12 mL septum-capped glass Exetainer vials (LabCo, UK) that had been purged with helium gas for 5 minutes. Duplicate vials were sampled for each incubation.

Vials were poisoned with 50% (w/v) zinc chloride and stored in the dark at room temperature. To obtain background isotopic composition of N2 gas, water from CTD casts was collected into Exetainers by overfilling the exetainer four times and closing the exetainer with a needle inserted to just below the septa, to cause any bubbles to be removed during closing. Exetainers were measured for 29N2 and 30N2 accumulation on a Thermo Delta V IRMS in continuous flow mode using helium gas at the University of Washington.

Allan Devol, Wendi Ruef and Rick Keil designed these in situ incubator trap systems. Megan Duffy, Allan Devol and Rick Keil from the University of Washington deployed and sampled these in situ incubator sediment trap systems. Clara Fuchsman from the University of Washington and Horn Point Laboratory, part of the University of Maryland Center for Environmental Science, ran the rate measurements on the mass spectrometer and did the initial data analysis.

Both Megan Duffy and Clara Fuchsman did further data analysis.