Metadata Report for BODC Series Reference Number 77057

• 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

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

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 Shackleton Cruise 2/81 CTD Data Documentation

Introduction

This data document covers the CTD data collected on RRS Shackleton Cruise 2/81 (October - November 1981) by the Department of Oceanography, Liverpool University, Liverpool, UK, under the direction of E.D. Barton.

Instrumentation

The instrument used was the University of Liverpool's Neil Brown MK III CTD with no modifications. This instrument has been described by Brown and Morrison (WHOI-78-23). No serious problems were encountered with the data acquisition or processing. The calibrations were satisfactory.

Sensor resolution was as follows:

Sampling Protocol

Casts were usually to a depth of approximately 600m with data collection on the downcast. A General Oceanics Rosette Sampler was attached 1 metre above the CTD. Regions of weak or no vertical gradient were chosen during the downcasts as likely calibration points, and water samples and reversing thermometer measurements were made on upcasts to provide in-situ calibration.

During the upcasts such sites were relocated with the CTD, the winch was stopped and, if conditions were not varying substantially, a Niskin bottle sample was taken and the CTD readings were noted. If the reversing thermometers were used, a five minute soak period was allowed for them to attain thermal equilibrium. In general, 2 or 3 protected thermometers were used for each sample.

The CTD sampling rate was approximately 30 scans/sec of pressure, temperature and conductivity.

CTD station positions were determined by satellite navigation and sea floor depths by precision depth recorder.

Calibration

Pressure

Before each cruise the pressure sensor was adjusted at zero and at full scale against a dead weight tester. Checks were also made at intermediate pressures. These showed no significant deviation from linearity.

Temperature

Comparisons were made against reversing thermometers, most of which had been recently recalibrated. Nine protected thermometers were used. There were 52 potential comparisons of 3 thermometers with CTD temperatures, discounting those made when the reversing frame hung up. 13 comparisons could not be made because of misfires or delayed reversals. There were 30 good comparisons when all three thermometers worked and gave reasonable results, 8 comparisons with two thermometers and 1 with one. The mean difference from all 107 comparisons was 0.006 °C (CTD lower); standard deviation 0.025 °C. No corrections were made to the CTD temperatures.

Salinity

Comparisons were made with 56 water bottle sample salinities determined by a Plessey laboratory salinometer. Salinity determinations were carried out by one person within one day of sampling. The CTD conductivity cell was cleaned daily. The mean difference from the comparisons was 0.068 PSU (CTD higher); standard deviation 0.014 PSU. No appreciable drift was found in the conductivity cell calibration and the CTD salinities were adjusted down.

Data Processing

The data were processed on Liverpool University's ICL 1906S computer. Data were affected by an intermittent fault which produced some occasional erroneous values. These were eliminated by identifying scans which contained pressure, temperature or conductivity values that lay outside prescribed limits, had excessive differences compared with surrounding values, or had pressure values more than 0.5db less than the preceding scan. Scans containing suspect values were removed. Edited values were averaged over 30 scans corresponding to a 1 second average and a pressure change of between 0.5 and 1db. Calibration corrections were applied and salinity calculated.

The CTD was fitted with a fast response thermistor; therefore no time lag correction was required.

There were no significant gaps in the data. Salinity has been calculated in Practical Salinity Units, as recommended by UNESCO. The data set consists of 30 scan averaged data, linearly interpolated to 2db intervals.

Note that the latitudes supplied for stations 2/47 and 2/138 have been amended as follows:

The latitudes supplied gave rise to unrealistic speeds for RRS Shackleton between stations. It has not been possible to check with the data originator whether these amendments are correct.

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.

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: