Metadata Report for BODC Series Reference Number 58268

• 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

Guildline 8705 CTD

The 8705 CTD is a conductivity-temperature-pressure profiler designed for marine applications down to depths of 6000 m. The instrument includes an anodised aluminium tube with a steel cage to protect the temperature and conductivity sensors and a urethane cap to protect the pressure sensor.

Specifications

* Conductivity specifications are given in terms of equivalent salinity

Further details can be found in the manufacturer's specification sheet.

RV Cirolana 8/1982 CTD Data Documentation

Introduction

This data document covers the CTD data collected on RV Cirolana 8/1982 (September - October 1982) by the Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, UK, under the direction of K.J. Medler.

Instrumentation

The instrument used was a Guildline Model 8705 Digital CTD which measured pressure, temperature and conductivity. The CTD was used alongside a General Oceanics Rosette Multisampler fitted with water bottles and was fitted with an acoustic altimeter with digital display to measure the height of the CTD above the sea bed.

Sampling Protocol

Lowering and retrieval speeds of 1 m/s were employed. Bottle sample and reversing thermometer measurements were made on ascent and sea water samples were analysed using a Guildline Autolab Salinometer.

Calibrations

Pressure

Calibrated in the laboratory before and after the cruise using a deadweight tester at carefully selected temperatures. A correction term of the form:

deltaP = A * T (CTD) + B + P (CTD) + C

is obtained and applied as

P (corrected) = P (CTD) + deltaP

The calibration is checked in the field when possible by using altimeter measurements of height above the sea bed.

Temperature

The temperature sensor was calibrated in the laboratory immediately before and after the cruise using platinum resistance thermometers. A correction equation is obtained by fitting the difference between the CTD and platinum resistance thermometers to a quatratic equation using least squares.

T (corrected) = T (CTD) + deltaT

where deltaT = A * T(CTD² + B * T(CTD) + C

The calibration is checked in the field by comparing the CTD data with reversing thermometer measurements.

Salinity

A comparison between in situ conductivity ratio of water samples (calculated using the algorithms given by Fofonoff and Millard (1983)) and measured CTD conductivity ratio enables coefficients a, b and c to be found in the equation:

CR (sample)/CR (CTD) = a * T + b * P + C

The CTD conductivity ratio is then corrected by:

CR (corrected) = CR (CTD) * (a * T + b * P + C)

After correcting the CTD data, as described above, a comparison was made with the potential temperature (POTT) - Salinity (S) relationship suggested by Saunders (1983):

S = 34.698 + 0.098 * POTT for North Atlantic Deep Water where POTT is less than 2.7° C.

Good agreement was found with Saunders POTT-S relationship, but there was some evidence of non-linearity in the deepest layers. Despite this, the agreement in salinity is still good, usually within ±0.005.

The conductivity ratio calibration was carried out using 106 water samples, many being duplicates.

Data Processing

Data came in at 25 frames/sec and were logged on an Apricot disk, and could be plotted. At the end of each station the data were transferred to an HP1000 computer. The raw data were then averaged over 25 observations every 125 observations. This resulted in data values averaged over approximately 1db with a value every 5db.

Calibration coefficients and correction factors were applied. Derived quantities were computed from algorithms published by Fofonoff and Millard (1983).

References

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

Saunders, P.M. (1983).
CTD data from the north east Atlantic Ocean 31° N - 46° N, July 1982. RRS Discovery Cruise 130. Institute of Oceanographic Sciences. Report No. 165.

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: