D242 CTD Discrete Dissolved Oxygen Sampling Document
Originator's Protocol for Data Acquisition and Analysis
Sample collection
Discrete dissolved oxygen samples were provided from 110 CTD casts performed during the RSS Discovery cruise 242. One sample was taken from each Niskin bottle that had been fired and between one to four duplicate samples were taken on every cast from the deepest bottles. Samples were drawn through short pieces of silicon tubing into clear, pre calibrated, wide necked glass bottles and were fixed immediately on deck with maganese chloride and alkaline iodide dispensed using precise repeat Anachem bottle top dispensers. Samples were shaken on deck for approximately half a minute and if any bubbles were detected in the sample at this point a new sample was drawn. Samples were then left in the constant temperature laboratory, and shaken again 30 minutes after sampling. They were stored under water until analysis, a minimum of one hour after collection.
Sample analysis
The samples were analysed onboard using the Winkler whole bottle titration method with amperometric endpoint detection (Culberson and Haung, 1987) via a Metrohm 716 DMS Titrino. The samples were checked against an in house potassium iodate standard of 0.01 N at 20°C at the beginning of each analytical run and incorporated into the calculations.
A number of samples were analysed in duplicate. This was a limited number due to the large volume of samples required to be analysed daily. 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.
Further details are provided in the cruise report for cruise D242 , pages 59-60.
BODC Data Processing Procedures
The dissolved oxygen data were supplied to BODC in Pstar format containing duplicate dissolved oxygen data, the corrected dissolved oxygen data and a flag channel for the corrected value populated by quality flags as defined by WOCE Hyrographic Programme. These files were reformatted to ASCII format and the corrected oxygen 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 |
|---|---|---|---|---|---|
| botoxy | µmol/l | Concentration of oxygen {O2} per unit mass of the water body [dissolved phase] by Winkler titration | DOXYWITX | µmol/kg | No unit conversion necessary |
References
Culberson, C. H., and Haung, S., (1987). Automated amperometric oxygen titration. Deep Sea Res., 34, 875 - 880.
Cunningham, A.,(2000). RSS Discovery Cruise 242, 07 SEP - 06 OCT 1999. Atlantic - Norwegian Exchanges. Cruise Report No. 28 Southampton Oceanography Centre.
