AMT6 Nutrient (micromolar) measurements from CTD bottle samples
Originator's Protocol for Data Acquisition and Analysis
This data originates from analyses of bottle samples taken from 38 CTD casts.
The nutrient analyser used during the AMT-6 cruise was a five-channel Technicon AAII, segmented flow autoanalyser. The chemical methodologies used were: nitrate (Brewer and Riley, 1965), nitrite (Grasshoff, 1976), phosphate (Kirkwood, 1989), silicate (Kirkwood, 1989) and ammonia (Mantoura and Woodward, 1983) the nanomolar nitrate and nitrite detection methodology was from Garside (1982) and the nanomolar ammonia system was adapted from Jones (1991). Water samples were taken from the 30 litre CTD/Rosette system (SeaBird) and sub-sampled into clean Nalgene bottles. The analysis of the samples was completed within 3 hours of sampling. Clean handling techniques were employed to avoid any contamination of the samples, particularly by ammonia. No samples were stored.
Underway continuous sampling of surface water used the non-toxic water system. The water was filtered in-line (Morris et al., 1978), by a 0.45 µm Millipore filter, before analysis of the macronutrients. For the underway nanomolar ammonia system the Millipore filter was removed and the water was only course filtered through a stainless steel mesh. The results for the CTD and underway samples from the same approximate depth of 7 m then agreed. Underway sampling was carried out where possible for the nanomolar ammonia system, and where necessary. Where values exceeded 1 microgram, the five channel Technicon analyser was deployed for the other nutrients.
The maximum sampling depth was 200 m for the CTD samples and was the bottom depth for all CTDs where possible. There was one deep CTD (to 1500 m) in the north of the Canigo region, off the Iberian Peninsula. All CTD samples were analysed successfully with a negligible sample loss rate. One CTD section was lost due to poisoning of the Copper/Cadmium Nitrate reducing column by anoxic bottom water samples on one day of the Benguela study. As usual, the Technicon system showed its reliability and reproducibility in the extreme environment of marine research. The nanomolar nitrate/nitrite chemiluminescent system worked as well as could be expected, although this system was at the limits of its detection for many mixed layer samples from the oligotrophic stations, and the present detector is of insufficient sensitivity to show fine scale changes and variations at less than 10 nanomoles. The ammonia system performed well following an extensive pre-cruise rebuild, and again it will have produced unique measurements of ammonia concentrations from these parts of the world's oceans.
References Cited
Brewer P.G. and Riley J.P., 1965. The automatic determination of nitrate in sea water. Deep-Sea Research, 12, 765-772.
Garside C., 1982. A chemiluminescent technique for the determination of nanomolar concentrations of nitrate and nitrite in seawater. Marine Chemistry, 11, 159-167.
Grasshoff K., 1976. Methods of seawater analysis. Verlag Chemie, Weiheim: 317 pp.
Jones R.D., 1991. An improved fluorescence method for the determination of nanomolar concentrations of ammonium in natural waters. Limnology and Oceanography, 36, 814-819.
Kirkwood D.S., 1989. Simultaneous determination of selected nutrients in seawater. ICES CM1989/C:29, 12pp.
Mantoura R.F.C. and Woodward E.M.S., 1983. Optimisation of the indophenol blue method for the automated determination of ammonia in estuarine waters. Estuarine, Coastal and Shelf Science, 17, 219-224.
Morris A.W., Bale A.J. and Howland R.J.M., 1978. A filtration unit for use with continuous autoanalytical systems applied to highly turbid waters. Estuarine and Coastal Marine Science, 6, 105-109.
Instrumentation Description
Not relevant to this data set.
BODC Data Processing Procedures
Data were submitted to BODC in Microsoft Excel spreadsheet format and saved to the BODC archive with reference PML020107. Sample metadata were checked against information held in the database. Originator's sample ID was matched based on CTD cast and bottle firing depth. OIDs were present in the database for the CTD events in the format CTDxx, where xx was the cast number for the cruise.
The CTD36 samples were matched to the cruise report depths as it appears there was a keying error and the 50 m sample should have read 80 m. A similar discrepancy was observed for CTD51 sample keyed as 10m by originator should have been keyed 100 m according to Cruise Report.
There were replicate samples provided for one depth on a number of casts. The mean of the replicates were taken for each depth and the values entered into the database for the following samples.
| CTD cast | Depths |
|---|---|
| CTD26 | 65 m |
| CTD28 | 50 m |
| CTD30 | 55 m |
| CTD34 | 75 m |
| CTD36 | 60 m |
| CTD38 | 40 and 50 m |
| CTD40 | 28 m |
| CTD42 | 35 and 40 m |
| CTD43 | 20 m |
Although the cruise report indicates underway and nanomolar measurements were made, there were none supplied to BODC. The files also contained related data from incubations carried out during the cruise.
Parameter codes defined in BODC parameter dictionary were assigned to the variables. The data were assigned parameter codes defined in BODC parameter dictionary. Data loaded into BODC's database using established BODC data banking procedures.
A parameter mapping table is provided below;
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| Ammonium | µmol l -1 | Concentration of ammonium {NH 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | AMONAATX | µmol l -1 | - |
| Nitrate+Nitrite | µmol l -1 | Concentration of nitrate+nitrite {NO 3 +NO 2 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | NTRZAATX | µmol l -1 | - |
| Nitrite | µmol l -1 | Concentration of nitrite {NO 2 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | NTRIAATX | µmol l -1 | - |
| Phosphate | µmol l -1 | Concentration of phosphate {PO 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | PHOSAATX | µmol l -1 | - |
| Silicate | µmol l -1 | Concentration of silicate {SiO 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | SLCAAATX | µmol l -1 | - |
Data Quality Report
BODC has not been advised of any quality checks carried out by the data originator.
Problem Report
Not relevant to this data set.
