Nanomolar ammonium concentration data from the ETNP St P2 in October 2019

In October 2019, ammonium concentrations were measured at St P2 in the Eastern Tropical North Pacific on board the ship (the R/V Kilo Moana) using the o-phthaldialdehyde (OPA) method with sodium sulfite additive to prevent derivatization of non-ammonium molecules (Holmes et al., 1999). The OPA solution included OPA, sodium sulfite and borate buffer exactly as prescribed in the protocol, and was stored in a dark bottle. Samples were taken in 15 mL falcon tubes that had been pre-incubated in OPA solution overnight to remove any ammonium contamination. The tubes were then rinsed three times with sample water before sampling. The OPA solution was added to the sample immediately after sampling. Standards (50, 200, 500, 1000, 2000 nM) were made using water from 500 m depth. A standard curve was run with the samples from each cast. We considered samples with &gt;50 nM ammonium to be detectable in this dataset.This dataset supports the paper "<b>Contributions of Vertically Migrating Metazoans to Sinking and Suspended Particulate Matter Fuel N</b>_{<strong>2</strong>}<b> Production in the Eastern Tropical North Pacific Oxygen Deficient Zone</b>."