2018 SCOPE Falkor Mesopelagic Nitrification Rates

2018 SCOPE Falkor Mesopelagic Nitrification Rates Experiments to quantify ammonia and nitrite oxidation rates were conducted in the center of the upwelling eddy during the 2018 SCOPE Falkor-Eddies cruise in the North Pacific Subtropical Gyre. Incubations with 15N-labled NH4+ and NO2- were conducted on in situ arrays to quantify the vertical variability in rates of nitrification. Incubations explicitly aimed at understanding the influence of light on nitrifiers and rates of nitrification were conducted by collecting water from depths throughout the upper mesopelagic, and incubating it with 15N-NH4+ or 15N-NO2- at depths above and below the depth of collection, in the light and the dark. Samples were prepared for d15N-NOx determination via the denitrifier method. Samples that were spiked with 15NO2- for determination of NO2- oxidation rates were first amended with 10 µL of sulfamic acid (8% w/v in 20% hydrochloric acid) per mL of sample volume and incubated at room temperature for 1 – 2 hours to remove any unreacted NO2- prior to subjecting to the denitrifier method. The resulting 15N2O was analyzed by isotope ratio mass spectrometry at the University of California, Santa Barbara. The timestamp is in UTC