Metadata Report for BODC Series Reference Number 57216

• 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.

SeaTech Transmissometer

Introduction

The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.

Specifications

• Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
• Beam diameter: 15 mm
• Transmitted beam collimation: <3 milliradians
• Receiver acceptance angle (in water): <18 milliradians
• Light source wavelength: usually (but not exclusively) 660 nm (red light)

Notes

The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

Further details can be found in the manufacturer's Manual.

RRS Charles Darwin Cruises 3/85 and 9A/85 CTD Data Documentation

Introduction

This document covers the CTD data collected on RRS Charles Darwin Cruise 3/85 (May 1985) and RRS Charles Darwin Cruise 9A/85 (November 1985) by the Institute of Oceanographic Sciences (Deacon Laboratory) Godalming, Surrey, UK., under the direction of P. M. Saunders.

Instrumentation

The instrument used was a Neil Brown Instrument Systems CTD which measured pressure, temperature and conductivity and was fitted with a Beckman dissolved oxygen electrode. The CTD was used alongside a General Oceanics Rosette Multisampler with 12 water bottles, a 10kHz pinger, a bottom echo-sounder and a Sea Tech transmissometer.

Sampling Protocol

Lowering and retrieval rates of 1.0 m/s were employed and the sensors were flushed with distilled water on recovery. Bottle samples and reversing thermometer measurements were made on ascent and the sea water samples were analysed using a Guildline Autolab Salinometer. Reversing thermometers were calibrated before and after the cruise.

Calibration

Pressure

The deck pressure offset was stable and a value of 11db was assumed for all stations. The calibration equation used was:

P = 0.1 * PRAW - 11.0

The table below shows differences in pressures determined from pairs of reversing thermometers (protected and unprotected) and

simultaneous observations of CTD pressure.

Temperature

Laboratory calibrations of January and June 1985 confirm the stability of the platinum resistance sensor. The calibration equation used was:

T = 0.00049953 * TRAW + 0.026

A comparison is given in the table below between the CTD temperatures and reversing thermometers separating the deep and shallow measurements.

Salinity

The sample measurements were generally within 0.001PSU of the potential temperature (POTT) - practical salinity (S) relationship for POTT less than 2.6 °C

S = 34.698 + 0.098 * POTT

Standard sea water batch numbers P96 and P99 were used for standardisation of the bench salinometer on cruises 3 and 9A respectively. The cell factor required to bring provisional CTD salinities into agreement with this relation was determined for each station. The table below compares salinities derived from the rosette sampler and Guildline salinometer with the CTD values.

Oxygen

From a sample value of oxygen concentration (determined by the Winkler method) the fractional saturation content was obtained by normalising it by the appropriate saturation value. The Beckman oxygen cell also measures fractional saturation F, given by the equation:

ln F = ln I + ln C + aT + bp

where

I = oxygen probe current
T = ambient temperature (electrode temperature ignored)
p = pressure

At sea, using the shipborne computer, oxygen was calculated by lagging the ambient temperature measurement. Ashore, corrections were made to each station to bring the CTD data to agree with sample values. The comparison between sample oxygen concentrations and CTD oxygen values is shown in the table; because of low quality the oxygen data were discarded from Cruise 3/85.

Transmittance

Potential transmittance, which takes account of the increasing mass of clear water in the 1m path of the instrument with increasing depth, was calculated. No observations of transmittance were made on Cruise 9A/85.

Fit of CTD Data to Rosette Sample Values

Data from both cruises are combined in the above table.

The depth of the 5 °C isotherm is approximately 1800 db.

Data Processing

Original values were averaged over an interval of one second and calibration coefficients and correction factors applied. A time constant correction algorithm was employed to compensate for the slower response of the platinum resistance thermometer.

Differences between successive values of each parameter were examined; the mean difference and its standard deviation calculated and values greater than several standard deviations from the mean difference were checked. Genuinely suspect data were then replaced by interpolated values.

Derived quantities were computed from algorithms published by Fofonoff and Millard (1983). To remove the effect of ships heave data cycles were sorted by pressure before all values were averaged at 2db intervals, centred on 1db, 3dband so on

References

Saunders, P.M. 1986.
CTD data from the Madeira and Iberian Abyssal Plains: Charles Darwin Cruises 3/85 and 9A/85. Institute of Oceanographic Sciences, Report No. 227.

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: