D321B Dissolved Inorganic Nutrients Sampling Document
Originator's Protocol for Data Acquisition and Analysis
Water samples were collected from CTD stations throughout the cruise for the analysis of dissolved inorganic nutrients using an onboard Lachet Quickchem 8000 colorimetric flow injection autoanalyser. Samples were collected in 250 ml acid-cleaned polythene bottles directly from CTD spigots without the use of a tube. Samples were stored in the fridge and analysed (in triplicate) within 24 hours of collection. Salt corrections were performed by running a small number of Low Nutrient Sea Water samples during each sample batch run, with the mean result being subtracted from sample results.
References Cited
Sherwin, T. A. et al, (2007) 'Cruise D321B Reykjavic to Clyde via Rockall, Scotland and the Wyville Thomson Ridge', Internal Report No 255, Scottish Association for Marine Science.
Available - Cruise D321B Internal Report
BODC Data Processing Procedures
The nutrient data were supplied to BODC in Microsoft Excel spreadsheets. Values were extracted from these and loaded into BODC's ocean database under an ORACLE Relational Database Management System. Data that were considered unrealistic were flagged suspect.
Occasional uncertainties were noted between the cruise report CTD logsheets and the originator spreadsheets relating to which particular Niskin bottle was sampled. In most cases the uncertainty involved multiple bottles fired at the same depth, so assignment to bottle numbers was deemed somewhat arbitrary.
Data listed out from the BODC database are done so at a resolution deemed appropriate for that particular variable and the analytical procedure involved. In some instances this results in the listing out of zero values.
Content of data series
| Originator's Parameter | Unit | Description | BODC Parameter code | BODC Unit | Comments |
|---|---|---|---|---|---|
| Ammonium | µM | Concentration of ammonium in the water column | AMONAZZX | µM | n/a |
| Standard deviation of ammonium | µM | Concentration standard deviation of ammonium in the water column | AMSDAAZX | µM | n/a |
| Phosphate | µM | Concentration of phosphate in the water column | PHOSAAZX | µM | n/a |
| Standard deviation of phosphate | µM | Concentration standard deviation of phosphate in the water column | PHSDAAZX | µM | n/a |
| Silicate | µM | Concentration of silicate in the water column | SLCAAAZX | µM | n/a |
| Standard deviation of silicate | µM | Concentration standard deviation of silicate in the water column | SLCAAAZX | µM | n/a |
| Nitrate | µM | Concentration of nitrate in the water column | NTRZAAZX | µM | n/a |
| Standard deviation of nitrate | µM | Concentration standard deviation of nitrate in the water column | SDNTAAZX | µM | n/a |
Data Quality Report
A number of the values in the channels AMONAAZX and AMSDAAZX have negative values which have subsequently been flagged.
SAMS nitrate data quality warning
SAMS have notified BODC of a problem in the analytical procedure adopted for nitrate analysis on this cruise. The problem relates to the technique used to prepare the analytical standards, which results in nitrate (and consequently nitrite) values which are typically 10-15 % higher than they should be. Absolute data values should therefore be used with extreme caution.
