Metadata Report for BODC Series Reference Number 97372

• 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 salinity data were very noisy and should be treated with caution.

Inspection of the pressure records from this cruise revealed several negative values (by up to 3 dB) at the start of some profiles. Reasonable temperature and salinity values accompanied the negative pressures, which casts some doubt on the accuracy of the pressure calibration. The affected data values have been flagged as suspect.

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

Bissett-Bermann 9040 Conductivity Temperature and Depth

The basic configuration of the B-B 9040 CTD incorporates pressure, temperature and conductivity sensors which could be logged digitally. This system also made it possible to derive other parameters, such as salinity, depth and sound velocity.

The instrument was versatile and it was possible to attach a dissolved oxygen sensor or to change the CTD housing, allowing it to obtain data from deeper layers in the water column. The accuracy for salinity is ±0.02 ppt , and ±0.02°C for temperature.

This instrument was also known as the Plessey 9040.

RRS Challenger 11/83 CTD Data Documentation

Introduction

Documentation for the CTD data collected on RRS Challenger Cruise 11/83 (August 1983) by the Scottish Marine Biological Association, Oban, Argyll, Scotland, UK, under the direction of D. J. Ellett.

Data Collection

The instrument used was a Bissett Berman 9040 CTD system and the data were logged on a Hewlett Packard 9820 and stored in an integer format. Instrument lowering and raising speeds were between 0.5m/s and 1m/s. An acoustic pinger was placed above the CTD to give an accurate depth measurement, this could then be used to check the CTD pressure calibration. An NIO bottle with reversing thermometers was placed above the pinger, within 2m of the CTD system. A bottle sample was taken at the bottom of the cast providing the temperature and salinity are uniform at that point. If large temperature or salinity gradients were present then the bottle sample was triggered at a suitable site on the upcast. A surface salinity sample was also taken at the start of the dip.

Calibration

The CTD was not calibrated in the laboratory. The manufacturer's calibration was used and water samples taken to check the calibration and apply corrections where necessary.

Temperature

The manufacturer's calibration was used to convert the raw data to to physical units using the equation below:

Temperature (°C) = (10⁶/Pt -2238.68/55.84)
where Pt is the temperature period in microseconds

These values were then plotted against the water bottle (i.e. reversing thermometer) temperatures and a regression line fitted to the data such that:

Temperature(WB) = m x Temperature(CTD) + c

Then the regression coefficients (m and c) were applied to correct the CTD temperature data - these are given in the table below.

Conductivity

The manufacturer's calibration was used to convert the raw data to to physical units using the equation below:

Conductivity (mmho/cm) = (10⁶/Pc - 4995)/58.12 + 10
where Pc is the conductivity period in microseconds

The water bottle salinities and corrected CTD temperatures were used to calculate the water bottle conductivity values. These values were then plotted against the CTD conductivities and a regression line fitted to the data such that:

Conductivity(WB) = m x Conductivity(CTD) + c

Then the regression coefficients were applied to correct the CTD conductivity data - these are given in the table below.

Pressure

The depths from the acoustic pinger were noted where the bottle samples were taken and then used to check the calibration of the pressure sensor - unless calibration values were available from the reversing thermometers. The equation below was used to convert the pressure period to physical units.

Pressure = (10⁶/Pd - 9712)/0.26267
where Pd is the pressure period in microseconds

A regression fit was carried out using the calibration values and the slope and intercept determined. The pressure values could then be corrected using:

Pressure (CORR) = m x Pressure(CTD) + c

The fit of the CTD data to the water bottle calibration data is given in the table below:

Data Processing

Obvious wild points were edited out of the calibration file and the calibration programs run to obtain values for the slopes and intercepts for temperature, pressure and conductivity. These were then applied to the uncalibrated data. Conductivities were converted to conductivity ratios and then converted to salinities using UNESCO recommended routines and sigma-t was calculated. The data values were then sieved to ensure a minimum separation between pressure values of 1 dbar. The data were then visually inspected and major spikes flagged.

References

Sharples, F. (1987).
A new data bank of SMBA STD/CTD observations in the Rockall Trough 1975-84. SMBA Marine Physics Group Report No. 36.

Graham, J.M., Sharples, F., Meldrum, D.T. and Edwards, A. (1987).
STD observations in the Rockall Trough 1975-77. SMBA Marine Physics Group Report No. 39.

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

Fixed Station Information

DML The Minches Station 2L

The Minches Station 2L is one of six fixed CTD stations crossing The Minch between Sutherland (mainland Scotland) and north east of Stornoway (Isle of Lewis, Scotland). The station was established by scientists at Dunstaffnage Marine Laboratory (DML).

Related Fixed Station activities are detailed in Appendix 1

Fixed Station Information

DML The Minches CTD Sections

The Minch and Little Minch (collectively, The Minches), between the Outer Hebrides and the Scottish mainland, have been extensively surveyed since the late 1970s by numerous research and government institutes. The region contains several repeated hydrographic stations, which collectively form transects. These repeated survey transects represent the northern part of a greater network of similar sections on the western Scottish continental shelf, which were established by Dunstaffnage Marine Laboratory (DML).

Map of standard 'The Minches' CTD Stations

Map produced using the GEBCO Digital Atlas.

The triangles indicate the nominal positions of individual Line L stations; nominal positions of Line K and N stations are shown by the circles and squares respectively. Measurements made at repeated 'The Minches' CTD stations lie within a box bounded by co-ordinates 57.517° N, 7.075° W at the south west corner and 58.283° N, 5.3° W at the north east corner.

Nominal station details:

DML The Minches Line L: The Minch, Scotland (west coast mainland - north of Isle of Lewis)

DML Line K: The Minch, Scotland (south of Isle of Lewis - Isle of Skye - west coast mainland)

DML Line N: The Little Minch, Scotland (Isle of Skye - North Uist)

Related Fixed Station activities are detailed in Appendix 2

Fixed Station Information

DML The Minches Line L

The Minches Line L is a survey section in The Minch, Scotland, crossing between Eddrachillis Bay (Sutherland, mainland Scotland) and Broad Bay (to the north east of Stornoway, Isle of Lewis). The line comprises six fixed CTD stations, which were established as part of routine monitoring work on the Scottish continental shelf by Dunstaffnage Marine Laboratory (DML). Line L was occupied during the 1980s.

Nominal station details

DML The Minches Line L: The Minch, Scotland (west coast mainland - north of Isle of Lewis)

Related Fixed Station activities are detailed in Appendix 3

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: DML The Minches Line L Station 2L

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.

Appendix 2: DML The Minches CTD Sections

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.

Appendix 3: DML The Minches Line L

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.