Metadata Report for BODC Series Reference Number 1969145

• 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

Plymouth Marine Laboratory automated Winkler titration system

A custom-made titration system with photometric end-point detection designed by Dr Carol Robinson, Plymouth Marine Laboratory. Measures dissolved oxygen via winkler titration method Measures dissolved oxygen via winkler titration method. Key features include a metrohm Dosimat 765 burette and photometer. Precision: 0.1 umol/kg.

Currently no specifications sheet available.

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.

DY084 (AMT27) Winkler Titration Dissolved Oxygen Concentrations from CTD Bottles

Originator's Protocol for Data Acquisition and Analysis

Seawater samples were collected from each CTD cast deployed during the cruise, with four to fice samples per station and 352 samples collected in total. These samples were subsequently fixed and analysed via titration methods to assess Dissolved Oxygen (DO) concentration. DO was determined by automated Winkler titration with photometric end-point detection (Carritt and Carpenter 1966). The concentration of thiosulphate was calibrated every 3 days using a commercial 0.1N KIO₃ standard (Sigma-aldrich, FIXANAL). The pipettes used for dispensing reagents were gravimetrically calibrated prior to the cruise. A traceable thermometer was used for measuring the fixing temperature (VWR TD 121, serial number: 92405158).

Dissolved Oxygen in seawater is produced by photosynthesis and consumed by respiration and photochemical reactions in the surface. Equilibrium between dissolved DO in seawater and the atmosphere is maintained through air-sea gas exchange. DO was measured with a CTD Sea-Bird 43 oxygen sensor mounted on the CTD hydrocast on AMT27. The objective of this work was to calibrate the sensor using discrete samples from Niskin bottles which were analysed by automated Winkler titration.

References Cited

Carritt, D.E. and Carpenter, J.H. 1966. Comparison and evaluation of currently employed modifications of the Winkler method for determining dissolved oxygen in seawater; a NASCO report. J. Marine Res., 24: 286-318.

Instrumentation Description

Plymouth Marine Laboratory automated Winkler titration system.

Further information can be found here.

BODC Data Processing Procedures

Data were submitted to BODC during the cruise in an Excel spreadsheet for calibration of the Sea-Bird 43 oxygen sensor and archived under BODC accession number BOD170193. Sample metadata provided (CTD cast, rosette bottle number, depth and date) were checked against metadata already held in the database. Rosette position and depth were used to match the samples to those in the database. There were no discrepancies. The oxygen concentrations were provided in micromoles per litre so no unit conversions were required to convert to the BODC parameter code applied. The data were reformatted, assigned BODC parameter codes and loaded in BODC's samples database under Oracle Relational Database Management System.

The parameter mapping between originators parameters and BODC parameters is provided below;

Data Quality Report

The data originator supplied flags to accompany each sample (Flag 0=ok, 1=suspect, 999=fail). There were 11 occasions where the titration failed (negative titre volume). These samples were excluded from the final dataset and not ingested into the BODC database. Where samples were identified as suspect, these were due to one of the following reasons: sample affected by bubbles; the vents were left open on the CTD bottles; chipped stoppers possibly affecting sample volume or the temperature took a long time to read. The suspect data were loaded to the database and flagged with an 'L' flag (mprobable value - originator's quality control). The raw data file is available on request. 352 samples were collected during the cruise and of these, 348 data values were provided to BODC. 11 samples were excluded from the final dataset, which consists of 337 samples in total.

Project Information

PML National Capability

The Plymouth Marine Laboratory National Capability focuses on long term science concerned with basin/decadal variability of the Ocean.

Data Activity or Cruise Information

Data Activity

No Document Information Held for the Series

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: DY084_CTD_CTD030

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