Dataset: PNPC and Nitrogen Uptake Rates
Deployment: HRS1610

Particulate Carbon and Nitrogen (PNPC)

Whole water from three target depths (near surface, the depth above the Chl maximum (or near the bottom of the mixed layer), and the depth of the Chl maximum) at each station was collected from Niskin bottles into 10 L carboys and transported to the on-board laboratory where water samples were mixed and sub-samples (0.2–1.4 L) were collected onto pre-combusted GF-75 filters (Whatman®, nominal pore size 0.3 μm) in triplicate, for analysis of particulate nitrogen (PN) and carbon (PC) concentrations and the natural abundance of 15N and 13C. The filters were stored in cryovials and immediately frozen and stored in a freezer at -20 °C until analysis. Prior to their analysis, filters were dried at 40 ºC, pelletized in tin capsules, and analyzed on a Europa 20/20 isotope ratio mass spectrometer equipped with an automated N and C analyzer. The detection limit of the mass spectrometer was 0.0018 and 0.0005 atom% for 15N and 13C, respectively; these values were derived based on three times the standard deviation (3 × SD) of the atom% of 12.5 µg N and 100 µg C standards (n=40).

Nitrogen Uptake 

Parallel sets of triplicate whole water (0.5−2 L) from the three target depths mentioned above (near surface, above the depth of the Chl maximum (or near the bottom of the mixed layer), and at the depth of the Chl maximum) from 27 stations were dispensed from 10 L carboys into acid-cleaned polyethylene terephthalate glycol incubation bottles (NalgeneTM).

Nitrogen uptake incubations were initiated by amending incubation bottles with highly enriched (98−99%) 15N-labeled substrates (Cambridge Isotope Laboratories, Inc., USA), including ammonium chloride (15NH4Cl), potassium nitrate (K15NO3), potassium nitrite (K15NO2), and 15N- and 13C-labeled potassium cyanate (KO13C15N), urea (13CO(15NH2)2), and algal amino acid mixture.