AMT14 Ammonium (CTD and non-toxic supply) and Urea (CTD bottle) samples
Data Acquisition and Analysis
This data originates from analyses on samples collected with CTD rosette bottles from 41 casts for both ammonium and urea. Water samples were collected from a number of depths during the pre-dawn CTD cast using the Sea-Bird CTD rosette system throughout the cruise. Later in the cruise a number of mid-morning casts were sampled. Samples were collected directly from the Niskin bottle tap using a silicon rubber tube into 50 ml centrifuge tubes. Tubes were rinsed three times with the sample water and then sealed with polypropylene caps to minimise air contact. Samples for urea analysis were frozen and stored for analysis after the cruise.
Additional samples were taken from the surface non-toxic seawater supply at 1500h (ship's time) on a daily basis and analysed for ammonium concentrations.
Ammonium determinations were made using the manual method of Holmes et al. (1999), modified for 10ml sample volumes (after Johnson, UEA) and samples were measured on a Turner Designs TD700 fluorometer fitted with the CDOM filter kit.
Urea concentrations were determined 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 (Cast, Date, Lat, Lon, Depth) were checked against information held in the database for the CTD casts - there were a couple of minor depth discrepancies which were corrected after referring back to the data originator. Parameter codes defined in BODC parameter dictionary were assigned to the variables. The data were provided nano-mol per litre units which were converted to micro-mol 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.
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 |
---|---|---|---|---|---|
[NH4] | nmol l -1 | Concentration (nM sensitivity) of ammonium {NH 4 } per unit volume of the water column [dissolved plus reactive particulate phase] by nanomolar ammonium fluorometry after Kerouel and Aminot (1997) | AMONNAKA | µmol l -1 | n/a |
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 | µmol l -1 | n/a |
Data Quality Report
BODC were not advised of any specific QC checks carried out by the data orginator.
Problem Report
Not relevant to this dataset.