Metadata Report for BODC Series Reference Number 2126183

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

Metrohm 794 Basic Titrino Titrator

The Metrohm 794 Basic Titrino is an all-purpose titrator used for dynamic and monotonic determination of solution concentrations. Titration modes of the instrument are constant or depending on the titration curve variable dosing of the titration reagent and Endpoint-Titration. The operation modes include; Dynamic Equivalence-point Titration (DET), Monotonic Equivalence-point Titration (MET), Set Endpoint Titration (SET), pH Calibration (CAL), Measuring (MEAS) and Titration Procedure (TIP) which links various commands and methods to a titration procedure. All operating modes of the Titrino can be combined to perform extensive analytical sequences.

Ready-to-start methods for the most common applications are stored in the internal method memory for example; the determination of the hardness of drinking water, diazotation of sulfonamides and primary amines, and determination of the peroxid number of edible oil sand fats. The operator is free to modify and overwrite the methods or to create and store new titration sequences.

The instrument consists of an exchange unit with a small display, which can be connected to either a magnetic stirrer (728), propeller rod stirrer (802) or Ti stand (703 or 727). Data exchange with a PC is possible with the Metrodata VESUV Software and with Metrodata TiNet Software complete keypad remote control, data acquisition and evaluation via PC is enabled.

Further details can be found in the manufacturer's user manual.

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles and Lever Action bottles have a capacity between 1.7 and 30 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

UKOA D366 dissolved oxygen concentrations from CTD bottle samples

Originator's Protocol for Data Acquisition and Analysis

Water for the determination of the dissolved oxygen concentration was only taken from the stainless steel CTD casts and they were the first samples to be drawn from the Niskin bottles. Where possible, each depth was sampled in duplicate. This was made possible because in the vast majority of casts there were less than twelve depths. On the few occasions there were more than twelve depths then the sampling depths were chosen based on the oxygen profile provided by the CTD package. Any steep gradients in oxygen concentration were avoided. Any Niskins within the top 10m were generally not sampled as wave action can produce tiny bubbles in the samples and the oxygen trace can be highly irregular in this region unless there were only a few depths sampled in that particular profile.

The water was drawn through short pieces of silicon tubing into clear, precalibrated, narrow-necked glass bottles. The temperature of the water at the time of sampling was measured using an electronic thermometer probe. The temperature would be used to calculate any temperature dependant changes in the bottle volumes. Each of the samples was fixed immediately using 1 ml of manganese chloride and 1 ml of alkaline iodide, shaken thoroughly and left to settle for approximately thirty minutes. After this time they shaken again and then left for at least an hour before analysis but all were analysed within a day.

It should be noted that there were no dissolved oxygen samples analysed before station 7, cast 11 as there was no-one on board to undertake the analyses. There was also no dissolved oxygen analysis between station 41, cast 47 and station 57, cast 63 as participants were undertaking a very intensive sampling programme along two transects through a coccolithophore bloom. There were serious time restraints, both in terms of sampling and of analysis, and so it was felt dissolved oxygen sampling could be dropped from these stations. Finally, there was also no dissolved oxygen from station 69, cast 75 as this was a dedicated cast for coral sampling and so dissolved oxygen was not required. It is felt that there is enough data to successful calibrate the sensor for the whole cruise and so these missing stations will not have an adverse affect on the quality of the calibration.

The samples were analysed in the main laboratory following the procedure outlined in Holley and Hydes (1995). The samples were acidified using 1 ml of sulphuric acid immediately before titration and stirred using a magnetic stirrer. The Winkler whole bottle titration method with amperometric endpoint detection with equipment supplied by Metrohm UK Ltd was used to determine the oxygen concentration.

During the first days on the ship the sodium thiosulphate was made up with 50 g/l. The sodium thiosulphate needed at least one day to stabilise. The normality of the sodium thiosulphate titrant was checked using a potassium iodate standard. This was repeated several times throughout the cruise and especially once the reagents had been changed. The reagents were changed twice during this cruise. Sodium thiosulphate standardisation was carried out by adding the reagents in reverse order with, stirring in between, and then 10 ml of a 0.01M potassium iodate solution using an automated burette. The sample was titrated and the volume of sodium thiosulphate required was recorded. This was repeated until at least four measurements agreed to within 0.003 ml of each other. The average of these titrations was used to calculate the volume of sodium thiosulphate which was then used in the calculation of the final dissolved oxygen calculation.

A blank measurement was also carried out to account for the oxygen in the reagents. The reagents were added in reverse order, as for the sodium thiosulphate standardisation, and then 1 ml of the potassium iodate standard was added using an automated burette. This was titrated and the volume of sodium thiosulphate required was recorded. 1 ml of potassium iodate was again added to the same sample and it was titrated again. This was repeated a third time. The average of the second and third volumes of sodium thiosulphate was subtracted from the first. This process was repeated at least four times. The average blank value was then used in the calculation of the final dissolved oxygen calculation.

References Cited

Holley S.E. and Hydes D.J., 1995. Procedures for the determination of dissolved oxygen in seawater. James Rennell Centre for Ocean Circulation, Internal Document No. 20.

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 SOC120231. Sample metadata (Station, CTD cast, bottle number and depth) were checked against information held in the database. There were no discrepancies.

The concentration data were provided in micro-moles per litre. These units match the BODC parameter code units and a unit conversion was not applied. Where replicate measurements were provided the mean and standard deviation were calculated and loaded to the database.

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.

A parameter mapping table is provided below;

Data Quality Report

The data from cast 11 flagged as suspect by the data originator possibly due to a faulty alkaline iodide dispenser, these have been marked 'L' in the database. No values were flagged by BODC.

Problem Report

Not relevant to this data set.

Project Information

UKOARP Theme B: Ocean acidification impacts on sea surface biology, biogeochemistry and climate

The overall aim of this theme is to obtain a quantitative understanding of the impact of ocean acidification (OA) on the surface ocean biology and ecosystem and on the role of the surface ocean within the overall Earth System.

The aims of the theme are:

• To ascertain the impact of OA on planktonic organisms (in terms of physiological impacts, morphology, population abundances and community composition).
• To quantify the impacts of OA on biogeochemical processes affecting the ocean carbon cycle (both directly and indirectly, such as via availability of bio-limiting nutrients).
• To quantify the impacts of OA on the air-sea flux of climate active gases (DMS and N₂O in particular).

The main consortium activities will consist of in-situ measurements on three dedicated cruises, as well as on-deck bioassay experiments probing the response of the in-situ community to elevated CO₂. Most of the planned work will be carried out on the three cruises to locations with strong gradients in seawater carbon chemistry and pH; the Arctic Ocean, around the British Isles and the Southern Ocean.

Weblink: http://www.oceanacidification.org.uk/research_programme/surface_ocean.aspx

Data Activity or Cruise Information

Data Activity

BODC Sample Metadata Report for D366_CTD_D366071

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.

Related Data Activity activities are detailed in Appendix 1

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Appendix 1: D366_CTD_D366071

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