Dimethyl sulphide (DMS) and dimethylsulphoniopropionate (DMSP) concentrations from CTD bottle samples collected during AMT14
Originator's Protocol for Data Acquisition and Analysis
This data originates from analyses on samples collected from 44 CTD casts and one surface bucket sample during the cruise. Water samples were taken directly from the bottles in the Sea-Bird CTD rosette system. Along the AMT-14 cruise track, every pre-dawn CTD cast (approx. 0400hrs local time) was sampled for at least 8 depths (the light depths plus the 3 depths in and around the chlorophyll maximum). The surface bottle from the late morning CTD cast (approx. 1100hrs local time) was also sampled. 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 DMSPd samples were then then purged in the same manner as before. The DMSPp analyses used a sample of the headspace above the NaOH-filter medium injected directly onto the GC column.
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, CTD cast, latitude, longitude and depth) were checked against information held in the database. There were no discrepancies.
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 <GF/F 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 <GF/F phase] by filtration 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 | µmol 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:
| CTD cast | Depth | Originator's QC comment |
|---|---|---|
| CTD 20 | 4.3 | Poor DMS Chromatography |
| CTD 56 | 2.5 | DMS analysed late |
| CTD 56 | 6.9 | DMS analysed late |
| CTD 56 | 13 | DMS analysed late |
| CTD 56 | 24.5 | DMS analysed late |
| CTD 56 | 44.3 | DMS analysed late |
| CTD 56 | 85.2 | DMS analysed late |
| CTD 56 | 100.3 | DMS analysed late |
| CTD 56 | 115.1 | DMS analysed late |
| CTD 57 | 2.5 | DMS analysed late |
The data originator indicated the following samples were below detection limit but did not provide details of the detection limit.
| CTD cast | Depth (m) | DMS Conc. (nM) | DMSPd Conc. (nM) | DMSPp Conc. (nM) |
|---|---|---|---|---|
| CTD 18 | 124.2 | X | X | - |
| CTD 22 | 123.7 | - | - | X |
| CTD 26 | 134.9 | X | - | X |
| CTD 30 | 147.2 | X | - | X |
| CTD 30 | 163.6 | X | - | X |
| CTD 36 | 148.7 | X | - | - |
| CTD 38 | 120.8 | - | - | X |
| CTD 44 | 69.1 | - | - | X |
| CTD 47 | 64.4 | - | - | X |
| CTD 50 | 75.5 | - | - | X |
| CTD 56 | 115.1 | X | - | X |
| CTD 59 | 124.3 | - | - | X |
| CTD 67 | 150.7 | - | - | X |
| CTD 71 | 140.8 | - | - | X |
| CTD 75 | 1.4 | - | - | X |
Problem Report
Not relevant to this data set.
