Data Parameters and Units:
The following is a list of data parameters for each file within the dataset: local date (MM/DD/YYYY); local time (HH:MM, 24-hour clock); GMT Date (MM/DD/YYYY); GMT Time (HH:MM, 24-hour clock), Latitude (decimal degrees) longitude (decimal degrees), station, Depth m (meters), Urea uM N (micromolar nitrogen), NO3 (uM) nitrate micromolar, NO2 (uM) nitrite micromolar, SILICA uM (micromolar), NH4 (uM) ammonium (micromolar), PO4 (uM) phosphate (micromolar), TDP (uM) total dissolved phosphorus (micromolar)
Methods:
Environmental data were collected aboard the R/V Weatherbird II and the R/V Bellows. A CTD-rosette was deployed between the surface (2 m) and up to a maximum depth ranging from 5 m to about 1,450 m, depending on the bottom depth of the station. Niskin bottles were fired at these depths and other pre-determined depths on the upcast. Water samples were collected during more than one CTD cast at some stations where water demand was high or the depth was >200 m. The Weatherbird II rosette held 12-12 L Niskin bottles, and the Bellows rosette held 12-5 L Niskin bottles. Gloves were worn to collect water samples. The order of water samples drawn from Niskin bottles was: gases, nutrients, chlorophyll, pigments (HPLC), CDOM, other. Nutrients: Nutrients were collected from Niskin bottles into acid cleaned wide mouth HDPE 30 mL bottles. Bottles and caps were rinsed three times, filled up to the shoulder of the container, and then frozen upright at -20 C. Samples were analyzed for nitrate (NO3 µM), nitrite (NO2 µM), phosphate (PO4 µM), silica (SiO2 µM), and ammonium (NH4 µM) by R. Masserini, A. Yunker, and K. Fanning (USF) following recommendations of Gordon et al. (2000) for the WOCE WHP project. The analytical system employed is a five-channel Technicon Autoanalyzer II upgraded with new heating baths, proportional pumps, colorimeters, improved optics, and an analog to digital conversion system (New Analyzer Program v. 2.40 by Labtronics, Inc.) Silica was determined by forming the heteropoly acid of dissolved orthosilicic acid and ammonium molybdate, reducing it with stannous chloride, and then measuring its optical transmittance. Phosphate was determined by creating the phosphomolybdate heteropoly acid in much the same way as with the silica method. However, its reducing agent is dihydrazine sulfate, after which its transmittance is measured. A heating bath is required to maximize the color yield. Nitrite was determined by the Bendschneider and Robinson (1952) technique, in which nitrite is reacted with sulfanilamide (SAN) to form a diazotized derivative that is then reacted with a substituted ethylenediamine compound (NED) to form a rose pink azo dye, which is measured colorimetrically. Nitrate was determined by difference after a separate aliquot of a sample is passed through a Cd reduction column to covert its nitrate to nitrite, followed by measurement of the "augmented" nitrite concentration using the same method as in the nitrite analysis. In the analytical ammonia method, ammonium reacts with alkaline phenol and hypochlorite to form indophenolblue. Sodium nitroferricyanide intensifies the blue color formed, which is then measured in a colorimeter on our nutrient-analyzer. Precipitation of calcium and magnesium hydroxides is eliminated by the addition of sodium citrate complexing reagent. A heating bath is required. The USF/CMS version of this technique is based on modifications of published methods such as the article by F. Koroleff in Grasshoff (1976). These modifications were made at Alpkem (now Astoria-Pacific International, Inc.) and at L. Gordon's nutrient laboratory at Oregon State University. Detection Limits (micromolar) for Nutrient Analyses: Nitrate + Nitrite = 0.22, Nitrite = 0.02, Silicic Acid = 0.29, Ammonium = 0.38, Phosphate = 0.09. Reference: Gordon L.I.; Jennings Jr, J.C.; Ross, A.A.; Krest, J.M. 2000. A Suggested Protocol For Continuous Flow Automated Analysis of Seawater Nutrients. WOCE Operation Manual, WHP Office Rept 90-1, WOCE Rept 77 No 68/91, 1-52; revised by Ross, A.A. Urea Measurements. To determine urea concentrations, seawater samples were collected from Niskin bottles using tygon tubing with 153 µm mesh filter attached to remove large zooplankton. Sample waters were passed through pre-combusted (450° C, 2.5 hrs) 25 mm Whatman GF/F filters (nominal pore size 0.7 µm) under low vacuum pressure and duplicate 10 mL aliquots of filtrate were poured into HDPE plastic scintillation vials and frozen (-20° C) until processed. In the lab, 10 mL of sample was pipetted into glass tubes containing 1.1 g NaCl. Tube racks were placed in a cool pan of water and 1.4 mL of the sulfuric acid reagent was added. After mixing the sample, 0.3 mL of the diacetylmonoxime reagent was added to the sample tube and vortexed until all NaCl was dissolved. The tube racks were then placed in an oven and heated at 75° C for two hours. Samples were read at an optical density of 520 nm on a Beckman DU720 Spectrophotometer. Detection Limit = 0.05 micromolar. Reference: Koroleff, F. 1976. A modified manual method for the determination of urea in seawater using diacetylmonoxime reagent. Estuarine, Coastal and Shelf Science 34 (5): 429-438. Total Dissolved Nitrogen Samples Seawater samples were collected in acid cleaned wide mouth HDPE 30 mL bottles and analyzed following methods in Valderrama (1981). Total dissolved nitrogen (TDN) concentrations were determined by the oxidation of dissolved organic nitrogen (DON) in filtered samples to nitrate. Samples are treated with potassium persulfate, boric acid, and sodium hydroxide and then autoclaved for 30 minutes at 121°C and 15 lb/in^2 pressure to convert DON, ammonium, and nitrite to nitrate. The nitrate concentrations of the oxidized samples, determined colorimeterically following the recommendations of Gordon et al. (2000), are equal to the TDN. DON is derived by subtracting the total inorganic nitrogen (TIN) value, determined seperately, from the TDN value. Reference: Valderrama, J. C. 1981. The simultaneous analysis of total nitrogen and total phosphorus in natural waters. Mar. Chem. 16: 109-122. Total Dissolved Phosphorus Measurements. To determine total dissolved phosphorus (TDP), seawater samples were collected from Niskin bottles using tygon tubing with 153 µm mesh filter attached to remove large zooplankton. Gloves were worn during sample collection. Sample waters were passed through pre-combusted (450° C, 2.5 hrs) 25 mm Whatman GF/F filters (nominal pore size 0.7 µm) under low vacuum pressure and duplicate 10 mL aliquots of filtrate were poured into fired scintillation vials (450° C, 2.5 hrs). Samples were then treated with 0.2 mL of 0.17 M MgSO4 and frozen (-20° C) until processed. In the lab, scintillation vials were placed in a drying oven at 95° C. Upon desiccation, the scintillation vials were fired in a muffle furnace at 450° C, for 2.5 hours. The samples were than hydrolyzed with 3 mL of 0.75 M HCl and heated for 20 minutes. An additional 7 mL of distilled water was added to the vial and heated for another 10 minutes. The samples were then transferred into test tubes, treated with 1 mL of mixed reagent and read at an optical density of 885 nm on a Beckman DU720 Spectrophotometer. Detection Limit = 0.05 micromolar. Reference: Solarzano, L. & J.H. Sharp. 1980. Determination of total dissolved phosphorus and particulate phosphate in natural waters. Limnol. Oceanogr. 25: 754-758. Nutrient data are provided in excel files. Each cruise is in a separate excel file, with station data on different spreadsheets within the cruise excel file.
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