PO300_2 discrete inorganic nutrient samples from CTD bottles
Data originator
Tim Brand, Scottish Association for Marine Science, UK
Cruise principal scientist
Colin R Griffiths, Scottish Association for Marine Science, UK
Originator's protocols
Cruise PO300_2 had various objectives, including an occupation of the Extended Ellett Line. The cruise sailed on the 19th July 2003 from Glasgow and returned there on the 6th August 2003, with a brief stop in Ullapool on 26th July 2003.
Water samples were collected from the CTD rosette into 2 litres polythene sample bottles. Up to 12 samples were taken from each cast. From these, subsamples were passed through 25 mm diameter Whatman GF/F filters and the filtrate collected in 250 ml acid-cleansed polythene bottles. These were immediately frozen for analysis back on land. Analysis was conducted using a Lachat Quik Chem 8000 flow injection autoanalyser, with triplicates of each sample run to establish instrumental precision. Standards were prepared using deionised water.
BODC processing
The data were provided to BODC in the form of an Excel workbook. The values contained within the spreadsheet were loaded to an ORACLE Relational Database. The originator did not always note the exact rosette bottle from which each sample was drawn (just the water depth). Where multiple bottles were fired at the same depth, samples were arbitrarily assigned to one of those rosette bottles. Matlab was used to enable some basic screening of the data to take place, with negative data values being flagged suspect.
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.
Contents of data series
| Originator's variable | Originator's units | BODC Parameter code | BODC's units | Comment |
|---|---|---|---|---|
| Ammonium | µM | AMONAAD1 | µM | - |
| Ammonium (standard deviation) | µM | SDAMAAD1 | µM | - |
| Phosphate | µM | PHOSAAD1 | µM | - |
| Phosphate (standard deviation) | µM | SDPHAAD1 | µM | - |
| Silicate | µM | SLCAAAD1 | µM | - |
| Silicate (standard deviation) | µM | SDSLAAD1 | µM | - |
| Nitrate | µM | NTRAAAD1 | µM | This parameter represents the amount of nitrate measured alone. |
| Nitrate (standard deviation) | µM | NTRASD03 | µM | This parameter represents the standard deviation of nitrate measured alone. |
| Nitrite | µM | NTRIAAD1 | µM | - |
| Nitrite (standard deviation) | µM | SDNIAAD1 | µM | - |
Note: BODC list values out of our database to a precision deemed appropiate to the analytical procedure adopted. This has resulted in several instances of zero values within the nitrate, nitrite and ammonium data for this cruise. Original values, as supplied by the originator, are preserved in our archive.
BODC Quality Control Flags
The following single character qualifying flags may be associated with one or more individual parameters within a data cycle:
| Flag | Description |
|---|---|
| Blank | Unqualified |
| < | Below detection limit |
| > | In excess of quoted value |
| A | Taxonomic flag for affinis (aff.) |
| B | Beginning of CTD Down/Up Cast |
| C | Taxonomic flag for confer (cf.) |
| D | Thermometric depth |
| E | End of CTD Down/Up Cast |
| H | Extrapolated value |
| I | Taxonomic flag for single species (sp.) |
| K | Improbable value - unknown quality control source |
| L | Improbable value - originator's quality control |
| M | Improbable value - BODC quality control |
| N | Null value |
| O | Improbable value - user quality control |
| P | Trace/calm |
| Q | Indeterminate |
| R | Replacement value |
| S | Estimated value |
| T | Interpolated value |
| U | Uncalibrated |
| W | Control value |
| X | Excessive difference |
