Temperature, salinity, oxygen concentration and saturation, and PAR were measured using a Sea-Bird SBE-911+ CTD platform equipped on the rosette deployment system. Fluorescence was measured via the rosette system using a WetLabs ECO AFL/FL platform.
Samples for NO3-/NO2- and NO2- were gravity filtered through 0.8 µm Nucleopore polycarbonate filters using acid cleaned in-line polycarbonate filter holders, then frozen (-20oC) in HDPE bottles until analysis on an Alpkem Flow Solution IV (Dore et al. 1996).
Soluble reactive phosphorus was measured after preparation via the magnesium-induced coprecipitation method (Karl and Tien 1992; Lomas et al. 2010).
Particulate organic carbon (POC), nitrogen (PON), and phosphorus samples were filtered on precombusted Whatman GF/F filters and frozen until analysis. After thawing, POC/PON filters were allowed to dry overnight at 65◦C before being packed into a 30 mm tin capsule (CE Elantech, Lakewood, New Jersey). Samples were then analyzed for C and N content on a FlashEA 1112 nitrogen and carbon analyzer (Thermo Scientific, Waltham, Massachusetts). POC and PON concentrations were calibrated using known quantities of atropine. Particulate organic phosphorus samples (POP) are analyzed using a ash-hydrolysis method (Lomas et al., 2010)
For chlorophyll, ~ 250–500 mL seawater was filtered onto 25-mm Ahlstrom glass fiber filters (nominal pore size 0.7 μm) under low pressure (15 kpa), and frozen immediately at −80_C. Samples were extracted in 90% acetone in the dark for 14–18 h at −20_C and quantified on a Turner 10-AU fluorometer using the acidification method (Parsons et al. 1984).
For cell counts, samples of whole seawater were collected in 2-mL centrifuge tubes, fixed with freshly made 0.2 -μm-filtered paraformaldehyde (0.5% v/v final concentration) for 1 h at 5_C in the dark, and counted on a FACSJazz or Influx flow cytometer (BD, Franklin Lakes, NJ, U.S.A.) utilizing a 200 mW 488 nm laser, with detectors for forward scatter, side scatter, 530 nm, and 692 nm. Prochlorococcus populations were discriminated based on forward scatter and red fluorescence, and a gate in orange (585 nm) discriminated for Synechococcus. Picoeukaryotic phytoplankton were all the red auto fluorescing cells that did not fit the Cyanobacteria gating scheme with a cell size below 2 – 3 μm.
See https://www.rvdata.us/search/cruise/NH1418 for further details.
For published methodologies please see the Related Publications section.
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