Dimethyl sulphide (DMS) and dimethylsulphoniopropionate (DMSP) concentrations from surface underway samples collected during AMT12
Originator's Protocol for Data Acquisition and Analysis
This data originates from analyses on samples collected from the ship's non-toxic supply each day at either 1600hrs (until 25/05/03) or 1500hrs local time. Samples were collected for dissolved DMS and DSMP (DMSPd) and particulate DMSP (DMSPp) where samples were collected using a GF/F filter with a nominal pore size approx. 0.7µm.
DMS and DMSP were analysed using a system termed 'Purge and Trap'. An inert gas was bubbled through the water sample to purge out the gaseous DMS. The released DMS gas was then trapped onto an adsorbant surface (Tenax) at a low temperature. Having concentrated all the DMS onto the trap, the gas was released onto the gas chromatograph (GC) column by heating the trap. The GC provided a measurement of how much DMS was in the volume of seawater purged and, using a calibration curve, a concentration was calculated. For DMSP, the process was exactly the same, but with an initial preparation step. This involved adding concentrated sodium hydroxide (NaOH) to the sample for dissolved DMSP (DMSPd) or to the filter paper for particulate DMSP (DMSPp) analysis which cleaved DMSP into DMS plus acrylic acid. The resulting DMS was then purged in the same manner as before.
References Cited
Instrumentation Description
Not applicable for this data set.
BODC Data Processing Procedures
Data were submitted via email in an Excel spreadsheet archived under BODC's accession number UEA050041. Sample metadata (Date, time (GMT), latitude, longitude and depth) were checked against information held in the database. The sampling times had been converted to GMT from local time in the file provided by the data originator. There was one discrepancy - the time of sampling on 12/06/2003 was given as 16:00 GMT and the cruise report shows underway sampling at 15:00 GMT for this date. The latitude and longitude provided match the ship's position at 15:00 GMT and so the data have been loaded against this time and position.
The concentration data were provided in nanomoles per litre. These units for the concentration data were consistent with the BODC parameter code units and no conversions were applied.
The data were reformatted and loaded in BODC's samples database under Oracle Relational Database Management System. Data were marked up with BODC parameter codes and loaded into the database. Individual samples were matched through CTD cast and depth.
A parameter mapping table is provided below;
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| DMS Conc. (nM) | nmol l -1 | Concentration of dimethyl sulphide {DMS} per unit volume of the water body [dissolved plus reactive particulate <unknown phase] by filtration, purging, cryogenic trapping and gas chromatography | DMSXGCD1 | nmol l -1 | n/a |
| DMSPd Conc. (nM) | nmol l -1 | Concentration of dimethylsulphoniopropionate {DMSP} per unit volume of the water body [dissolved plus reactive particulate <unknown phase] by Millipore prefiltration and gas chromatography | DMSPGCD1 | nmol l -1 | n/a |
| DMSPp Conc. (nM) | nmol l -1 | Concentration of dimethylsulphoniopropionate {DMSP} per unit volume of the water body [particulate >GF/F phase] by filtration and gas chromatography | DIMSUM01 | nmol l -1 | n/a |
Data Quality Report
BODC was advised by the data originator of a number of quality issues with the data and these data points were flagged 'L' within the database. These are summarised in the table below:
| Date | Time (GMT) | Originator's QC comment |
|---|---|---|
| 31/05/2003 | 17:00 | DMSPd uncorrected for DMS purge efficiency |
Problem Report
Not relevant to this data set.
