Metadata Report for BODC Series Reference Number 973933

• 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 Charles Darwin 86 CTD Data Documentation

Instrumentation

The CTD profiles of the water column and water samples at discrete horizons were taken with a Seabird SBE 911 plus CTD mounted inside a 22 bottle rosette array. The CTD probe incorporated a pressure sensor, conductivity cell, pressure protected high quality thermistor and a membrane dissolved oxygen sensor. In addition, attached to the CTD frame, were a Chelsea Instruments Mk III Aquatracka fluorometer, a Chelsea Instruments Mk III Aquatracka nephelometer and a SeaTech red light (661 nm) transmissometer with a 25 cm path length.

The rosette frame was equipped with twenty-two 12 litre NOEX bottles. The bases of the bottles were 0.5 m above the pressure head with their tops 0.5 m above it. One of the bottles was fitted with a holder for up to three digital reversing thermometers mounted 0.3 m above the CTD temperature sensor. As usual, there were intermittent problems with the NOEX bottles from contamination by leakage.

An underway CTD routine check station was held on 20th May. This was followed by a programme of CTD profiles of the water column along the OMEX transect with consecutive water sampling at discrete horizons.

Lowering rates were generally in the range of 0.5-1.0 m sec-1 but could be up to 1.5 m sec-1. Bottle samples and reversing thermometer measurements were acquired on the ascent of the CTD casts. Salinity determinations of bottle samples were partially done on board ship with the remainder being completed at the laboratory after the cruise. Oxygen concentrations from the majority of the bottle samples were also obtained on board by Winkler titration.

Data Acquisition

The data were logged on a PC using the SeaBird data acquisition software.

Post-Cruise Processing

The SeaBird DATCNV program was used for the conversion from binary raw data files to ASCII format in engineering units (PSU, °C, etc.). The data were then passed to Dr. Hendrik van Aken's group at NIOZ who worked up the temperature, salinity and oxygen channels. Details of the procedures used are not known but this group are associated with the collection of WOCE data and there is every reason to believe that the work was done to a very high standard.

The processed data were supplied to BODC.

Reformatting

The data as supplied had been binned to 1db with temperature (ITS90), practical salinity, chlorophyll (calibrated to µg/l), oxygen (µmol/kg), attenuance (per m) and nephelometer output (arbitraty units).

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the graphics editor. In addition to reformatting, the transfer program applied the following modifications to the data:

Dissolved oxygen was converted from µmol/kg to µM by multiplying the values by (1000+sigma-theta)/1000.

The chlorophyll was converted back to a voltage by a natural log transform to conform to the requirements of the BODC CTD data handling system. On retrieval, the data as supplied are reproduced.

Editing

Using a custom in-house graphics editor, the limits of the downcasts were delimited by manually applying flags to the cycle number channel.

No flagging of data other than garbage in the attenuance channel at depths greater than 2000 m on a couple of casts were required.

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

Calibration

The salinity and temperature data had been calibrated prior to submission to BODC. No further calibration was required.

Inspection of the attenuance data showed the values in clear water to be too high, typically about 0.5. This is probably because no air correction had been applied to the data. Analysis of the data showed that the transmissometer was exceptionally stable and therefore a uniform correction factor (-0.132) was applied to all casts to normalise the data to a clear water value of 0.35.

The oxygen data were checked against the bottle data and this confirmed that the oxygen data had been calibrated against the bottle data set.

No extracted chlorophyll data were available for this cruise and consequently the data presented are the result of a nominal calibration. More heed should therefore be paid to the relative, rather than absolute, chlorophyll values.

Data Reduction

Once all screening and calibration procedures were completed, the data set was binned to 2 db (casts deeper than 100 db) or 1 db (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. Oxygen saturations have been computed using the algorithm of Benson and Krause (1984).

Data Warnings

The fluorometer has not been calibrated against extracted chlorophyll data. The absolute values may therefore be meaningless.

References

Benson, B.B. and Krause, D. 1984. The concentration and isotopic fractionation of oxygen dissolved in fresh water and sea water in equilibrium with the atmosphere. Limnol. Oceanogr. 29 pp.620-632.

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

Further details can be found in the manufacturer's 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.

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

Fixed Station Information

OMEX I Moored Instrument and CTD site OMEX1

OMEX1 was one of four fixed stations for the OMEX I project. It was visited by seven cruises and collected a variety of data during the period June 1993 to September 1995. These include:

• Mooring deployment
• CTD casts
• Bottom landers
• Box and multi cores
• Plankton recorders
• Stand alone pumps

The data collected a site OMEX1 lay within a box bounded by co-ordinates 49° 24.1'N, 011° 34.0'W at the southwest corner and 49° 25.7'N, 011° 24.4'W at the northeast corner, with an approximate depth of 670 metres.

Related Fixed Station activities are detailed in Appendix 1

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: OMEX I site OMEX1

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.