Dataset: Total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) of samples collected on the West Florida Shelf during STING II cruise EN704 on R/V Endeavor from Jul 1 to Jul 12, 2023

Water column samples were collected in July 2023, on the West Florida Shelf during STING II cruise EN704 on R/V Endeavor, 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 into 60 mL HDPE bottles and frozen at -20 C until analysis on land. 

TDP concentrations were measured using a Shimadzu UV-1800 and a Shimadzu UV-1900i. All reagents were prepared in dedicated labware with high purity Milli-Q (>18.2 MΩ cm) water. Samples were calibrated using a 6 point calibration curve with concentrations that bracketed sample concentrations. Each run included multiple Milli-Q water and reagent blanks, as well as three internal standards including adenosine triphosphate, a polyphosphate compound, glyphosate, a polyphosphonate compound, and 0.2 µm filtered oligotrophic surface water from the Gulf to check the consistency of the TDP concentration analysis over time.

TDN concentrations were measured using a Thermo 42i NOx analyzer and a Teledyne T200 NOx analyzer and were calibrated with standards that bracketed the concentration range of samples. Additionally, as an internal check on the completeness of the persulfate oxidation method, DON standards were included as “unknowns” in each set of persulfate oxidation, in this case USGS 40 (L-glutamic acid) and IAEA600 (caffeine).