PARAGON 1 - KM2112 - Iron Uptake In Situ Measurements

This dataset contains measurements of in situ rates of dissolved iron (Fe) uptake collected during the PARAGON 1 expedition (KM2112) in the North Pacific Subtropical Gyre. Measurements come from daily collections of whole seawater at 150 m using trace metal clean techniques. Rates of iron uptake were measured by subsampling 250 mL aliquots of whole seawater into polycarbonate bottles and spiking with a final concentration of 0.4 nmol L⁻¹ ⁵⁵FeCl₃ with a specific activity of 2.74 Ci mmol⁻¹ of Fe (Perkin Elmer). A killed blank measurement was also made by spiking an additional 250 mL aliquot with a final concentration of 1% glutaraldehyde prior to spiking with ⁵⁵FeCl₃. All aliquots were then incubated in the dark at in situ temperature for 8-10 hours. Incubations were terminated by filtering the entire 250 mL aliquot for each sample through a 0.2 µm polycarbonate filter. In order to remove extracellularly bound Fe, filters were rinsed 3 times with an oxalate wash according to Tang and Morel (2006) followed by three rinses with 0.2 µm filtered seawater. Filters were then transferred to high density polyethylene scintillation vials and submerged in 10 mL of Ultima Gold LLT scintillation cocktail (Perkin Elmer). Radioactivity incorporated into microbial biomass was measured on a TriCarb 4910TR scintillation counter. Values reported are blank-corrected averages of triplicate measurements from each sample but have not been adjusted for isotope dilution resulting from unlabeled iron present in situ. Timestamp is in UTC.