Metadata Report for BODC Series Reference Number 275796

• 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

The data are derived from instruments that were laboratory calibrated but not recalibrated using in-situ sample data, resulting in data of variable quality.

The data originators believe the temperatures to be reasonable but believe the salinity data to be of a quality too poor to be of value to physical oceanographic studies.

Climatological checks indicate that the salinity values are 0.4-0.5 ppt too low.

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

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Specifications

These specification apply to the MK3C version.

Further details can be found in the specification sheet.

RRS John Biscoe Cruise 04 CTD Data Documentation

Introduction

Documentation for the CTD data collected on RRS John Biscoe Cruise 04 (27 Jul - 29 September 1983) by the British Antarctic Survey, Cambridge, U.K., under the direction of R.B. Heywood.

Instrumentation

The instrument used was a Neil Brown Instruments System Mark IIIB CTD. Observed parameters were pressure, temperature and conductivity. All sensors were calibrated before and after the cruise. Up to 12 water bottles were mounted on a Rosette sampler and 4 pairs of reversing thermometers were attached. Water bottles were triggered on the downcast at 10m and at the bottom of the cast, the remainder being fired on the upcast (mainly for chemical samples). Data were collected on the downcast.

Calibration

Reversing thermometers were calibrated at the Deacon Laboratory of the Institute of Oceanographic Sciences. The pressure sensor was compared with a Bourdon gauge which had been calibrated at the National Physical Laboratory. The accuracy of the temperature data is thought to be ± 0.01°C.

Data Processing

Calibrations were applied and the data despiked by rejecting data values outside of predetermined tolerances. Data values were then averaged to provide data at 1 decibar intervals.

Note that it was not possible to recover and reprocess all of the data collected on this cruise to produce 1 decibar values. For those casts which were not reprocessed an earlier version of the data is held by BODC. Few processing details are available for these casts. Calibrations were applied and the data despiked by rejecting data values outside of predetermined tolerances. Derived quantities were computed from algorithms published by Fofonoff and Millard (1983). The data were averaged to provide values at the following depths:

• Every 5m from 5m to 100m
• Every 10m from 110m to 200m
• 250m, 260m, 280m, 300m, 325m, 350m, 375m, 400m, 425m, 450m, 500m
• 600m, 700m, 800m, 900m, 1000m, 1200m, 1500m, 2000m

Calibration

Salinities from the bottle samples were determined at the British Antarctic Survey using a Guildline Salinometer. Some time after these data were supplied to BODC the salinometer was found to be faulty which casts doubt on the accuracy of the salinity values. The CTD casts that were not reprocessed were:

Data Quality

The salinity data from the CTD have been compared with other measurements made in this region and also with the Levitus Atlas. The data which have not been reprocessed are within about 0.01 ppt of data collected on various cruises including Discovery II (1929-31) and within about 0.02 ppt of the Levitus Atlas salinities. The reprocessed salinity data are between approximately 0.4 - 0.5 ppt lower than the data which has not been reprocessed.

Reference

Fofonoff, N.P. and Millard Jr., R.C. 1983.
Algorithms for the computation of fundamental properties of sea water. UNESCO Technical Paper on Marine Science 44

Heywood, R.B. 1984.
British Antarctic Survey Offshore Biological Programme Cruise 4 (27 July - 29 September 1983) Report

Levitus, S. 1982.
Climatological Atlas of the World Ocean. NOAA Professional Paper No. 13. US Government Printing Office. 173pp

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

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: