Dataset: Field physiochemical parameters including nutrient concentrations and nitrogen specific uptake rates from samples collected between 2017 and 2019 from the Arctic Ocean, California Coastal Current, and a Chesapeake Bay estuary

Site water for incubation experiments and for the analysis of ambient nutrients was collected slightly differently for each of the sampling regions. In the Arctic, site water for incubation experiments was collected on the R/V Ukpik and R/V Sikuliaq (cruise ID number SK201712S) during the summer of 2017 using a submersible pump and CTD rosette, respectively. In Baja, sampling occurred twice on the R/V Robert Gordon Sproul during both May and October 2017 (cruise ID numbers SP1714 and SP1727), and site water was collected using a CTD rosette (Turk-Kubo et al. 2021). In Virginia, surface sites in the York River were sampled by directly filling an acid-washed PETG carboy over the side. Filtrations for sample filtrate and filters also varied. These York Rivers samples were obtained during day trips aboard a variety of small powerboats (<21 feet), every other month from June 2018 to July 2019. Powerboats are housed out of the Virginia Institute of Marine Science.

In the Arctic, filtrations were conducted in parallel, which separately passed site water through a larger Nucleopore Membrane filter (3.0 micrometer (μm) nominal pore size) and a smaller Whatman GF-75 filter (nominal pore size 0.3 μm). This same combination of filters was used in Baja in October 2017. In May 2017, Baja sampling used the same filters, but filtered sequentially, meaning that site water was first passed through the Nucleopore filter before passing through the GF-75. The York River site samples were only filtered using the GF-75. Filtrate for all regions was collected from the GF-75 filtration and kept for later nutrient analyses and filters were used for chlorophyll a analysis.

Pigments (chlorophyll a and phaeopigments) were measured after extraction with 90% acetone overnight (Parsons et al. 1984; Arar and Collins 1997). Concentrations of ammonium were analyzed using the Koroleff (1983) method and amino acids were measured as dissolved primary amines (DPA; Parsons et al. 1984). Concentrations of nitrate, nitrite, phosphate, and silica were measured using a Lachat 8500 Quickchem autoanalyzer. Urea was analyzed using the monoxime method (Price and Harrison 1987). Concentrations of total dissolved nitrogen and dissolved organic carbon were assessed using a Shimadzu TOC-V TNM (Hansell 1993). Dissolved organic nitrogen is calculated as the difference between total dissolved nitrogen and inorganic nitrogen. 

Nitrogen uptakes were measured after incubation for a set time (1 to 24 hours) in either 0.5 or 1-liter PETG bottles. Stable isotope tracer methods were used according to those described in Baer et al (2017). Uptake rates for inorganic and organic nitrogen were measured by incubating water with 15N- ammonium, nitrate, creatine, urea, and/or an amino acid mixture under in situ light and temperature conditions in a flow-through system on deck or in a cold room set to ambient site water temperatures. Rate incubation experiments were terminated with the same filtration methods as collection of site water ambients with the exception that a Sterlitech silver filter was used in lieu of the Nucleopore Membrane filter. The exact combination of nitrogen substrates varied between sites and regions. All nitrogen uptake samples were analyzed on a Sercon Integra 2 isotope ratio mass spectrometer.

Known Issues/Problems:
Note that for the October sampling in the Baja region, chlorophyll a concentrations for the nutrient size fractions are unavailable. Instead, chlorophyll a concentrations for the >0.7 μm size fraction are available thanks to the Arrigo and Zehr dataset (listed under "Related Datasets").