AMT3 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 25 CTD casts.
The concentrations of nutrients were measured colourimetrically using a 4-channel, Technicon auto-analyser with standard methodologies. All depths from the CTD (typically 10) were measured on each cast, generally within 2 hours of collection. Surface samples taken at approximately 4 hourly intervals were stored at 4 o C and analysed with the samples from the following CTD cast.
All samples were analysed except for one batch where the phosphate channel was lost temporarily. There were a number of technical problems throughout; these consisted of: 1) noisy colourimeter responses initially, particularly for the silicate channel, which was also prone to drift non-linearly. However this improved with time and became less problematic as the voyage progressed. 2) All the colourimeters blew bulbs, sometimes frequently. 3) The orange-green pump tubes in the present batch only lasted a few days despite being run for only 4-5 hours per day. All the analytical results were stored as colourimeter responses on paper traces and were digitised to then convert to quantitative results. Quantitatively the surface water concentrations were below detection levels for the analysis and the data were not submitted to BODC.
References Cited
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 PML010014. Sample metadata were checked against information held in the database. Originator's sample ID was matched based on latitude/longitude and bottle firing depth. Station/Sample reference provided is the Julian Day (JD) that sampling took place on. These were matched to the CTD casts that took place each day on the cruise. Two casts took place at around 10:00 (ship's time) each day.
OIDs were present in the database for the CTD events in the format xxxCTDy, where xxx was the Julian Day and y the number of the CTD cast for that day. The cruise report indicates on JD266 there was no bottle sampling from the first cast of the day and on JD269 the nutrient samples were collected from the second cast. On all other days the nutrients were sampled from the first cast of the day. The data has been linked to these events accordingly. There were replicate samples provided at both the 7 and 50 m depths sampled on JD277. The mean was taken for each depth and these values have been entered into the database.
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 |
|---|---|---|---|---|---|
| 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.
