AMT12 Ammonium and Urea nanomolar measurements
Data Acquisition and Analysis
This data originates from analyses on CTD rosette bottles from 27 casts. Water samples were collected from 6 depths during the pre-dawn CTD cast using the Sea-Bird CTD rosette system. Samples were collected into acid clean 60 mls HDPE (nalgene) sample bottles. Clean handling techniques were employed to avoid any contamination of the samples.
Ammonium determinations were made on frozen seawater samples due to technical complications prohibiting such measurements during the cruise. This is recognised as a suspect practice so the data should be viewed/used with caution. The manual method of Holmes et al (1999) was used, modified for 10ml sample volumes (after Johnson, UEA) and samples were measured on a Turner Designs TD700 fluorometer fitted with the CDOM filter kit. This is the first time (to the PI's knowledge) that this technique was used for AMT.
Urea concentrations were again determined on frozen samples using the room temperature manual method of Goeyens et al. (1998) adapted from Mulvenna and Savidge (1992). All samples were read on a Hitachi 810 Spectrophotometer.
References Cited
Goeyens L., Kindermans N., Abu Yusuf M. and Elskens M. 1998. A room temperature procedure for the manual determination of urea in seawater. Est. Coast. Shelf Science, 47, 415-418.
Holmes R.M., Aminot A., Kerouel R., Hooker B.A. and Peterson B.J. 1999. A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Can. J. Fish. Aquat. Sci. 56, 1801-1808.
Johnson M.T. 2004. The air-sea flux of ammonia, PhD Thesis, University of East Anglia, Norwich.
Mulvenna P.F. and Savidge G., 1992. A modified manual method for the determination of urea in seawater using diacetylmonoxime reagent. Est. Coast. Shelf Science, 34, 429-438.
Instrumentation Description
Not relevant to this dataset.
BODC Data Processing Procedures
Data were submitted to BODC in Microsoft Excel spreadsheet format. Sample metadata (Station, Light (%), Bottle Depth (m)) were checked against information held in the database - there were no discrepancies. Parameter codes defined in BODC parameter dictionary were assigned to the variables. The data were provided nano-mole per litre units which were converted to micro-mole per litre by dividing by 1000. The units were then consistent with those used for the relevant parameters in the BODC database. NB: the data are from nanomolar analysis and the 4th decimal place can be considered to be significant.
In the file two samples (CTD51 depth 61m and CTD58 depth 20m) referred to data that was not present and were not loaded.
Data loaded into BODC's database with only a unit conversion change applied.
A parameter mapping table is provided below;
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| Ambient [Ammonium] | nmol l -1 | Concentration (nM sensitivity) of ammonium {NH4} per unit volume of the water column [dissolved plus reactive particulate phase] by nanomolar ammonium fluorometry after Kerouel and Aminot (1997) | AMONNAKA | umol l -1 | Data were divided by 1000 for unit change |
| Ambient [Urea] | nmol l -1 | Concentration (nM sensitivity) of urea per unit volume of the water column [dissolved plus reactive particulate phase] by manual analysis using the diacetylmonoxime method | UREAMDTX | umol l -1 | Data were divided by 1000 for unit change |
Data Quality Report
BODC were not advised of any specific QC checks carried out by the data orginator.
Problem Report
The data originator advises that since the ammonium determinations were made on frozen seawater samples, which is recognised as a suspect practice, the data should be viewed/used with caution.
