Metadata Report for BODC Series Reference Number 920115

• 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 MKII CTD

This instrument was designed for precise fine scale measurements of salinity and temperature in the deep ocean.

The conductivity sensor is a miniature four electrode cell and the temperature is measured by a combination of of a miniature fast thermistor and a platinum resistance thermometer. Pressure is measured using a strain gage bridge transducer.

The precise value of each parameter is determined by measuring the ratio of the sensor interface output voltage to the input voltage.

The original specifications are as follow:

This instrument is no longer in production and it is not known if support and maintenance are still available

References Cited

Brown, Neil L., 1974. A precision CTD microprofiler. IEEE International Conference on Engineering in the Ocean Environment, Ocean 74, pp 270-278.

FS Valdivia 137 CTD Data Documentation

Instrumentation

The CTD profiles were taken with a Neil Brown Mk2 CTD incorporating a pressure sensor, conductivity cell and platinum resistance thermometer. The CTD unit was mounted vertically in the centre of a protective cage. Attached to the bars of the frame was a Chelsea fluorometer. However, this failed to return any useful data.

A rosette sampler fitted with 12, 2.5 litre Niskin bottles was mounted above the frame.

Data Acquisition

The data were logged using the EG&G CTDACQ program running on a PC.

On-Board Data Processing

The raw data logged by CTDACQ were written onto Quarter Inch Cartridge tapes using the Everex tape streamer backup facility.

Post-Cruise Processing

Reformatting

The raw data were extracted from the Quarter Inch Cartridge tapes on a PC running the Everex software at the British Antarctic Survey in Cambridge and transferred to BODC as compressed files on floppy disk. The Chelsea Instruments CTDPOST program, which is compatible with the EG&G format, was used to convert the binary files into 1db binned calibrated files in ASCII. These were transferred to a UNIX workstation and converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the workstation graphics editor.

Editing

Using a custom in-house graphics editor, the limits of the downcasts were manually flagged. In addition, spikes on all the downcast channels were manually flagged 'suspect' by modification of the associated quality control flag. In this way none of the original data values were edited or deleted.

Once screened, the CTD downcasts were loaded into a database under the Oracle relational database management system.

Calibration

Pressure

The pressure offset is usually determined by looking at the pressures recorded when the CTD was clearly logging in air. Few data points were logged in air and therefore the minimum pressure of each cast was used to derive a pressure correction. Using the logic that at the start of the cast the pressure should read about 1.5db a consistent pressure offset was observed throughout the cruise thus:

Temperature

A CTD temperature calibration exercise was carried out using data from the deep sea classical reversing thermometers included with the CTD data. The following offsets were determined:

However, comparison of the profiles from the deep casts with data from other cruises known to be of good quality showed that the temperatures as recorded were much nearer the true values than the data with the corrections described above applied. Consequently, the reversing thermometer data have been deemed unreliable and no corrections have been applied to the temperature data.

Salinity

In order to calibrate the conductivity sensor of the probe, water samples were taken at selected stations and analysed on board using a salinometer. From these, the following offsets were determined for the CTD salinity data:

However, a comparison of deep station T/S curves with other cruises known to be of good quality showed the CTD on this cruise to be reading 0.016 PSU high, not low as implied by the corrections above. It has therefore been concluded that the bottle salinity data from this cruise are unreliable and a correction of -0.016 PSU has been applied to all CTD salinities from this cruise.

Chlorophyll

It has not been feasible to retrieve the fluorometer data. The Chelsea Instruments processing software refused to recognise the presence of a fluorometer channel in the raw data. Data were only available for a small number of casts due to the instrument flooding when the top plate deformed under a pressure of 6000 db. Consequently, it was not deemed cost effective to pursue the only options open (purchasing the EG&G software or writing custom software) to recover such a small amount of data.

Data Reduction

Once all screening and calibration procedures were completed, the data set was binned to 2 db (casts deeper than 100 db) or 1db (casts shallower than 100 db). The binning algorithm excluded any data points flagged suspect and attempted linear interpolation over gaps up to 3 bins wide. If any gaps larger than this were encountered, the data in the gaps were set null.

Downcast values corresponding to the bottle firing depths were incorporated into the database.

Project Information

Ocean Margin EXchange (OMEX) I

Introduction

OMEX was a European multidisciplinary oceanographic research project that studied and quantified the exchange processes of carbon and associated elements between the continental shelf of western Europe and the open Atlantic Ocean. The project ran in two phases known as OMEX I (1993-1996) and OMEX II - II (1997-2000), with a bridging phase OMEX II - I (1996-1997). The project was supported by the European Union under the second and third phases of its MArine Science and Technology Programme (MAST) through contracts MAS2-CT93-0069 and MAS3-CT97-0076. It was led by Professor Roland Wollast from Université Libre de Bruxelles, Belgium and involved more than 100 scientists from 10 European countries.

Scientific Objectives

The aim of the Ocean Margin EXchange (OMEX) project was to gain a better understanding of the physical, chemical and biological processes occurring at the ocean margins in order to quantify fluxes of energy and matter (carbon, nutrients and other trace elements) across this boundary. The research culminated in the development of quantitative budgets for the areas studied using an approach based on both field measurements and modeling.

OMEX I (1993-1996)

The first phase of OMEX was divided into sub-projects by discipline:

• Physics
• Biogeochemical Cycles
• Biological Processes
• Benthic Processes
• Carbon Cycling and Biogases

This emphasises the multidisciplinary nature of the research.

The project fieldwork focussed on the region of the European Margin adjacent to the Goban Spur (off the coast of Brittany) and the shelf break off Tromsø, Norway. However, there was also data collected off the Iberian Margin and to the west of Ireland. In all a total of 57 research cruises (excluding 295 Continuous Plankton Recorder tows) were involved in the collection of OMEX I data.

Data Availability

Field data collected during OMEX I have been published by BODC as a CD-ROM product, entitled:

• OMEX I Project Data Set (two discs)

Further descriptions of this product and order forms may be found on the BODC web site.

The data are also held in BODC's databases and subsets may be obtained by request from BODC.

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: