D242 Discrete CTD Salinity and Temperature Sampling Document
Originator's Protocol for Data Acquisition and Analysis
Sample collection
Discrete salinity samples were taken from 124 CTD casts performed during the RSS Discovery cruise 242. At least one sample was taken from each Niskin bottle that had been fired, using 200 ml glass sample bottles which were closed with disposable plastic inserts and screw-on caps. Each bottle and cap was rinsed three times with sample water to remove any old sample and salt crystals from the neck of the bottle. The bottle was then filled to the base of the neck, the top of the bottle and the bottle neck were wiped dry, and then the bottle was then sealed with a plastic insert. Samples were left in the constant temperature laboratory for at least 24 hours before being analysed in order for the temperature to equilibrate. Discrete samples were also drawn from the ship's non-toxic underway supply at approximately four hour intervals for calibration purposes.
In addition, two SiS RTM 4002 X digital reversing thermometers were used on rosette position one (serial number T1545) which also recorded the standard deviation of the mean temperature that it measured; and rosette position four (serial number T995). SiS pressure meters were also attached on rosette position one (serial number P6534) and four (serial number P3694), the data for which have not been loaded into BODC's database or undergone BODC processing or quality control.
Sample analysis
The samples were analysed onboard using a Guildline Autosal 8400A salinometer set at 21°C which was located in the constant temperature laboratory, where temperatures were controlled to 18°C. The salinometer was standardised against standard seawater ampoules, and standards were run every one to two CTD casts, typically every 20 - 26 samples.
Duplicate samples were drawn from Niskin bottle 1 on each of the casts and also from a second bottle usually near half depth. In addition, repeat firing were sometimes made in the deepest water, which were "blind" to the analysts. In all 266 duplicates and repeats were taken.
Where duplicate samples were taken, a definitive data value was derived from the averaging of the two samples. There were instances were one of the duplicated samples were deemed of poor quality by the Originator and so in these cases only the good quality data values has been used.
BODC Data Processing Procedures
The salinity data were supplied to BODC in Pstar format containing duplicate salinity data and the corrected salinity data. The Originator supplied flagged channels for each of the corrected variables populated by quality flags as defined by WOCE Hyrographic Programme. These files were reformatted to ASCII format and the corrected salinity values and any associated flags were extracted and loaded into BODC's database under the ORACLE Relational Database Management System. Any further data that BODC considered unrealistic were flagged suspect.
Content of data series
| Originator's Parameter | Unit | Description | BODC Parameter code | BODC Unit | Comments |
|---|---|---|---|---|---|
| botsal | psu | Practical salinity of the water body by bench salinometer and computation using UNESCO 1983 algorithm | PSALBSTX | dimensionless | No unit conversion necessary |
| revtmp | degc90 | Temperature of the water body by reversing thermometer | TEMPRTNX | Degrees Celsius | No unit conversion necessary |
Originator's Data Quality
On 24 September the compressor which cools the laboratory ceased working during analysis of samples from CTD station 13693, due to an overloading of the ship's electric circuits. Salinity values from this cast should be treated as suspect at better than 0.002.
References
Cunningham, A.(2000). RSS Discovery Cruise 242, 07 SEP - 06 OCT 1999. Atlantic - Norwegian Exchanges. Cruise Report No. 28 Southampton Oceanography Centre.
