Dataset: Dissolved Macronutrient Concentrations from Depth Profiles and Incubation Experiments from STING I Cruise AE2305 on R/V Atlantic Explorer in the Gulf of Mexico from February to March 2023

Water column samples were collected in February and March 2023 aboard the R/V Atlantic Explorer using a trace metal clean rosette (SeaBird) outfitted with 12-L Niskin-X samplers (Ocean Test Equipment), a trace metal clean pump, or a custom surface pump “towfish” system (Mellett and Buck, 2020). Seawater samples for macronutrient analysis were filtered through 0.2 µm Pall Acropak Super membrane filter capsules, collected in acid-cleaned and triple-rinsed 15-mL Falcon tubes, and stored in ziplock bags in the fridge until analyzed shipboard following recommended practices (Becker et al., 2020), typically within 24 hours of collection. 

Samples were analyzed shipboard for phosphate, nitrate+nitrite, silicate, and nitrite on a QuAAtro39 AutoAnalyzer (SEAL Analytical) according to standard colorimetric methods (Strickland and Parsons, 1972). All reagents were prepared in dedicated labware with high purity Milli-Q (>18 MΩ cm) water. Working standards were prepared fresh daily in an artificial seawater (ASW; 35 g/L sodium chloride, 0.5 g/L sodium bicarbonate) matrix using calibrated volumetric pipettes. 

Nine-point standard curves were analyzed at the beginning of each run with multiple reagent blanks. Quality control checks were analyzed every twelfth sample with ASW blanks and standards. The highest standard from the calibration curve was analyzed approximately every twenty samples to check for drift during the runs. Subsamples of reference material for nutrients in seawater (Konso) were measured in each run (see Table 1 below). 

Detection limits for each parameter were determined from three times the standard deviation of replicate lowest standards. Limits of detection were 0.035 µM for phosphate, 0.048 µM for nitrate+nitrite, 0.051 µM for silicate, and 0.012 µM for nitrite. Values below detection are reported as 0 µM with accompanying QC Flag 6.