Dataset: Turnover Time Uptake Rate Bioassay Experiments

Sampling and analytical procedures:

Bioassay experiments were conducted at station 1 and stations 3. At each station, inorganic and organic phosphate amendments were performed on seawater with and without nitrogen enrichment  (NH4Cl, NaNO3). Bioassay Experiments consisted in incubating, over an incubation period of 48h, surface seawater (5m) with inorganic or organic phosphate compounds (20 µM; final concentration of P) including, polyphosphate (polyp), inorganic phosphate (Pi), nucleotides (ATP or AMP) and methylphosphonate (Mepn). In each incubation experiment, a control treatment (surface seawater without amendment) was included.

To investigate a potential abiotic hydrolysis of inorganic and organic phosphate compounds, duplicates of surface seawater sampled inshore (5 m) and previously autoclaved (120°C; 30 min), were incubated in parallel. The autoclaved seawater (1L) was amended with either Mepn, AMP, ATP or PolyP (final concentration 20 µM P).  

In the bioassay experiments, phosphate turnover time and uptake rates were determined using carrier free 32PO43- (orthophosphoric acid, 33.3–40.7 GBq mmol-1 from Perkin Elmer). After incubation with the radioisotope, 5-mL samples were gently vacuum filtered onto polycarbonate membranes (0.2 µm). Filters were rinsed with filtered seawater (<0.2 µm) and then transferred into scintillation vials. A volume of 4 mL of scintillation cocktail (ultima Gold, PerkinElmer) was then added and samples were counted on a Packard Tri-Carb liquid scintillation counter.  Bulk PO43- turnover times (TT, h) and uptake rates (nmol L-1 h-1) were calculated.

Instruments: Radioactivity was assayed on a  Packard Tri-Carb liquid scintillation counter

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