Nitrate, nitrite, phosphate, silicate and ammonium seawater concentrations for BAS cruise JR20030105
Originator's data acquisition and analysis
Discrete samples were taken either using a CTD water bottle rosette. Discrete samples were subsampled and passed through a mixed ester membrane (Whatman WME, pore size 0.45 µm; pre-soaked in dilute HCl and rinsed with water). All analyses were conducted using a nutrient autoanalyser made up of Technicon MK II single channel colorimeters and Ismatec pumps and custom built reaction manifolds.
Nitrite Nitrite was determined following the method described by Folkard (1978). Nitrite ions diazotise sulphanilamide then couple with N-1-naphthylethylenediamine dihydrochloride to form an azo-dye, the concentration of which is measured by absorbance at 550 nm.
Nitrate Determination of nitrate was conducted following the method described by Stainton (1974). Nitrate is reduced to nitrite by passing the sample stream through a transmission tube containing a copper-coated cadmium wire. Nitrite ions diazotise sulphanilamide then couple with N-1-naphthylethylenediamine dihydrochloride to form an azo-dye, the concentration of which is measured by absorbance at 550 nm.
Phosphate Phosphate concentration was determined following a method similar to that described by Tréguer and Le Corre (1975). Orthophosphate ions react with acidified ammonium molybdate in the presence of antimony to form phosphomolbdic acid. This is reduced by ascorbic acid to a 'molydenum blue' complex (Riley and Skirrow, 1975) the concentration of which is measured by absorbance at 630nm.
Silicate The concentration of silicate in seawater was determined using a method based on an industrial method by Technicon (1976). Silicate ions react with ammonium molybdate in acidic conditions producing silicomolybdic acid. This is reduced to a 'molybdenum blue' complex by ascorbic acid (Riley and Skirrow, 1975) and its concentration is measured by absorbance at 660 nm.
Ammonium Ammonia is determined using a variant of the Berthelot reaction. Sodium dichloroisocyanurate is used as a hypochlorite donor (Krom, 1984) and catalysis is performed by potassium ferrocyanide. After reagent additions, the reaction stream is heated to 40°C and formation of 'indophenol blue' is promoted under longwave UV radiation (365 nm). Concentration is measured by absorbance at 630 nm.
See Whitehouse, 1997 for full details of all instrumentation and analysis involved.
References cited
Folkard A.R., 1978 Automatic analysis of seawater nutrients. Fisheries Technical Report, 46, 23.
Krom M.D., 1984 Spectrophotometric determination of ammonia. A study of a modified Berthelot reaction using salicylate and dichloroisocyanurate. The Analyst, 105, 305-316.
Riley J.P. and Skirrow G., 1975. Chemical Oceanography, 3, (2nd Edition), London, Academic Press.
Stainton M.P., 1974. Simple, efficient reduction column for use in the automated determination of nitrate in water. Analytical Chemistry, 46, 1616.
Technicon Instruments Corporation, 1976. Silicates in water and wastewater. Technicon industrial method No 105-71.
Tréguer P. and Le Corre P., 1975. Manuel d'analyse des sels nutritif dans l'eau de mer(Utilisation de l'AutoAnalyser II, Technicon, 2nd edition). Report laboratoire d'oceanologie chimique, Université de Bretagne Occidentale, Brest, France.
Whitehouse M.J., 1997. Automated Seawater Nutrient Chemistry. British Antarctic Survey, Cambridge.
BODC Data Processing Procedures
Data were received by BODC in spreadsheet format with the nutrient data from various BAS cruises in labeled worksheets (BAS_nutrient_data_1981-2009.xls). The following metadata fields were also included with the data: cruise ID, date, latitude, longitude, event number and pressure.
Parameter codes defined in the BODC parameter dictionary were mapped to the variables as follows:
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| NO3 | mmol m -3 | concentration of nitrate + nitrite per unit volume of the water body (dissolved plus reactive particulate <0.4 µm phase) | NTRZAAD2 | µmol L -1 | No unit conversion necessary, units analogous with one another |
| NO2 | mmol m -3 | concentration of nitrite per unit volume of the water body (dissolved plus reactive particulate <0.4 µm phase) | NTRIAAD2 | µmol L -1 | No unit conversion necessary, units analogous with one another |
| NH4 | mmol m -3 | concentration of ammonium per unit volume of the water body (dissolved plus reactive particulate <0.4 µm phase) | AMONAAD2 | µmol L -1 | No unit conversion necessary, units analogous with one another |
| PO4 | mmol m -3 | concentration of phosphate per unit volume of the water body (dissolved plus reactive particulate <0.4 µm phase) | PHOSAAD2 | µmol L -1 | No unit conversion necessary, units analogous with one another |
| Si | mmol m -3 | concentration of silicate per unit volume of the water body (dissolved plus reactive particulate <0.4 µm phase) | SLCAAAD2 | µmol L -1 | No unit conversion necessary, units analogous with one another |
Nutrient data were received with no associated time for the sampling event. It was therefore deemed necessary to acquire times from the cruise event log, using the event numbers to map the correct times to the nutrient sampling events.
The depth of the water column at each sampling event has been assigned using GMT and GEBCO data .
The data were banked according to BODC standard procedures for sample data. Data were banked as received, with no averaging or other modifications applied.
Data Quality Report
There are no data quality issues to report.
