Dataset: Phytoplankton nitrate uptake rates collected during the 2012-2013 Palmer Field Season (WAP Carbon export project)

We conducted 12-h nitrate uptake experiments in on-land incubators.  Each incubator was cooled with flow-through seawater.  Nitrate uptake rates were typically conducted on 1-L samples collected from 0, 5, 10, 20, and 65 m.  Samples were placed in polycarbonate bottles and spiked with 15-N labeled nitrate, then placed in mesh shading to approximate 100% surface irradiance (0 m), 50% surface irradiance (5 m), 25% surface irradiance (10 m), 10% surface irradiance (20 m), and dark (65 m). These light levels were chosen to match Palmer LTER net primary production depths and light levels and are close to the seasonal average light levels at these depths, although actual light varied substantially throughout the season (see Stukel et al. 2015).  At the end of the 24-hour incubation, bottles were immediately vacuum filtered onto pre-combusted 25-mm GF/F filters. Filters were rinsed with filtered seawater, wrapped in foil and stored at  80°C. On land, samples were fumigated with HCl vapor to remove inorganic carbon, dried, and placed inside a tin cup for C/N and isotopic analysis at the UC Davis stable isotope facility. NO3- uptake rates in each incubation bottle (and associated uncertainties) were determined using equations in Dugdale and Wilkerson (1986). For additional details see Stukel et al. (2015).