D379 discrete dissolved inorganic nutrients sampling document
Originator's protocol for data acquisition and analysis
Water samples were drawn from CTD rosette bottles fired during the cruise for inorganic nutrient analysis. Ammonia, phosphate, silicate and nitrate+nitrite were targeted, with the majority of the sampling effort concentrated in areas of the water column corresponding with changes in water mass. 49 samples were also drawn from the ship's non-toxic water supply. Due to a faulty rotary valve the phosphate line stopped working during the cruise. As it was considered more important to measure phosphate rather than ammonia, the ammonia line rotary valve was swapped for the defective phosphate one.
Samples were collected in 125 ml acid cleaned polythene bottles directly from CTD spigots without the use of a tube. Samples were stored in a fridge prior to analysis. The analysis was carried out within 24 hours of sample collection with a Lachat Quick Chem 8500 flow injection autoanalyser using the manufacturer's recommended methods.
Samples were measured in triplicate to identify instrument precision. A stock-mixed standard was prepared in deionized water with subsequent dilutions made in OSIL Low Nutrient Sea Water using the instrument auto-dilutor facility. Five standard concentrations and a blank were run in all cases and new standards were prepared every 48 hours. Using standards prepared in Low Nutrient Sea Water removes the need to do a separate salt correction. Three standard concentration ranges were prepared for the non-toxic samples and those collected across the Wyville Thomson CTD transect, depending on expected nutrient concentration.
BODC data processing procedures
The nutrient data were supplied to BODC in Microsoft Excel format. Values were extracted from this file and loaded into BODC's ORACLE relational database. Standard deviatons were calculated by the Originator. Data that were considered unrealistic were flagged suspect. Metadata collected from the various data files were favoured by BODC over the metadata recorded in the cruise report logs present in the D379 cruise report.
Content of data series
| Originator's Parameter | Unit | Description | BODC Parameter code | BODC Unit | Comments |
|---|---|---|---|---|---|
| CTD bottle ammonium | µM | Concentration of ammonium in the water column by colorimetric autoanalysis (unfiltered) | AMONAATX | µM | N/A |
| Standard deviation of CTD bottle ammonium | µM | Concentration standard deviation of ammonium in the water column by colorimetric autoanalysis (unfiltered) | SDAMAATX | µM | N/A |
| CTD bottle and discrete underway phosphate | µM | Concentration of phosphate in the water column by colorimetric autoanalysis (unfiltered) | PHOSAATX | µM | N/A |
| Standard deviation of CTD bottle and discrete underway phosphate | µM | Concentration standard deviation of phosphate in the water column by colorimetric autoanalysis (unfiltered) | SDPHAATX | µM | N/A |
| CTD bottle and discrete underway silicate | µM | Concentration of silicate in the water column by colorimetric autoanalysis (unfiltered) | SLCAAATX | µM | N/A |
| Standard deviation of CTD bottle and discrete underway silicate | µM | Concentration standard deviation of silicate in the water column by colorimetric autoanalysis (unfiltered) | SLSDAATX | µM | N/A |
| CTD bottle and discrete underway nitrate/ nitrite | µM | Concentration of nitrate and nitrite in the water column by colorimetric autoanalysis (unfiltered) | NTRZAATX | µM | N/A |
| Standard deviation of CTD bottle and discrete underway nitrate/ nitrite | µM | Concentration standard deviation of nitrate and nitrite in the water column by colorimetric autoanalysis (unfiltered) | SDNZAATX | µM | N/A |
Data quality report
No problems reported and no significant issues encountered during BODC data banking procedures.
It has been noted, however, that the silicate value for the NUT008 sample was below the detection limit. This was conveyed by a low instrument signal. The user should be aware of this when using these data.
Two silicate values (sampled on CTD cast 98 and 102) and one nitrate/ nitrite value (sampled on CTD cast 18) were negative. These values have been assigned an 'M' flag by BODC.
References cited
Griffiths C. R. et al. , (2012). RRS Discovery Cruise D379, 31 Jul 2012 - 17 Aug 2012. Southampton to Reykjavic - the Extended Ellett Line. Scottish Association for Marine Science, 184pp. (Scottish Marine Institute, Oban.)
Available - Cruise D379 Internal Report
