Dataset: Concentrations of particulate phosphate in seawater collected during R/V Savannah cruise SAV-19-02 in the NW Atlantic Ocean in the Spring of 2019

Sampling and analytical procedures:

 Seawater samples were collected in triplicate from Niskin bottles (12 L), at three stations (St. 1, St. 2 and St. 3) along a transect from coastal Georgia to offshore waters. Latitude (lat) and longitude (lon) of sampling sites are provided in .mat files. Stations 1 and 2 were on the continental shelf (15–30 m depth), while Station 3 was on the shelf break (220 m depth) adjacent to the Gulf Stream. At each station, samples were collected at 2-3 depths between the surface (4–5 m) and 50 m for SRP, DOP and PP.  SRP (50 mL), DOP (50 mL) and PP (2 L) were sampled from Niskin bottles. SRP and DOP samples were filtered through 0.2 µm polycarbonate filters and transferred into high density polyethylene bottles (HDPE, 60 mL) and kept frozen (-20°C) until analysis. PP samples were filtered through pre-combusted (450°C, 4.5h) and acid washed (1N HCl) GF/F filters, using a peristaltic pump. PP filters were wrapped in pre-combusted (450°C, 4.5h) aluminum foil, and kept frozen (-20°C) until analysis.   

SRP, DOP and PP were analyzed following a spectrophotometric method based on the molybdenum reagent (Murphy and Riley, 1962). SRP concentrations were analyzed using the Liquid Waveguide Capillary Cell® (LWCC, optical length path = 2.5 m). DOP concentrations were determined by subtraction of SRP from the total dissolved phosphate (TDP). TDP was digested to SRP following the wet oxidation procedure (Pujo-Pay and Raimbault, 1994) and SRP was subsequently determined using the LWCC. PP concentrations were determined after high-temperature combustion (450°C, 4.5 h) and HCl extraction (0.5 N) (Strickland and Parsons, 1972). The released SRP following this procedure was then analyzed spectrophotometrically using a conventional spectrophotometer with a 10 cm cuvette.

Location:  Northwestern Atlantic surface waters. Depth: surface-50 m.

Instruments:  Sampling was performed using Niskin bottles (12 L) mounted on a rosette.  Measurements of SRP, DOP were performed using the Liquid wave guide capillary cell (2.5 m length path, model 3250, World Precision Instrument). PP samples were measured using a Gynesis spectrophotometer.