Metadata Report for BODC Series Reference Number 887429

• 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.

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.

RRS Charles Darwin 85 CTD Data Documentation

Instrumentation

The CTD profiles were taken with an RVS Neil Brown Systems Mk3B CTD incorporating a pressure sensor, conductivity cell and a platinum resistance thermometer. The CTD unit was mounted in a protective cage to which a Chelsea Instruments Aquatracka fluorometer was attached.

A General Oceanics rosette sampler fitted with 6, 1.7 and 6, 2.4 litre Go-Flo bottles was mounted above the frame. The bottles were fired in pairs to give 4 litres of water per sample. The bases of the larger bottles were approximately 40 cm above the CTD and their tops 1 m above it. The 1.7 litre bottles were fitted with a holder for up to three SIS digital reversing thermometers and/or pressure devices with their sensors approximately 85 cm above the CTD in their triggered position.

Lowering rates were in the range of 0.5-1.0 m/sec. Bottle samples and reversing thermometer measurements were acquired on the upcast.

Data Acquisition

The CTD data were sampled at a frequency of 32 Hz and reduced in real time by the RVS Level A microcomputer system to produce a 1-second time series. This was logged as digital counts on the Level C workstation via a Level B data buffer.

On-Board Data Processing

RVS software on the Level C (a SUN workstation) was used to convert the raw counts into engineering units (Volts for the fluorometer, mmho cm-1 for conductivity and °C for temperature). A nominal calibration (a simple antilog) was also applied to the chlorophyll channel by this program.

Data were written onto Quarter Inch Cartridge tapes in RVS internal format and submitted to BODC for post-cruise processing and data-banking.

Post-Cruise Processing

Reformatting

The data were converted into the BODC internal format to allow the use of in-house software tools, notably the graphics editor. The nominal calibration applied to the fluorometer data was removed, returning the data to raw voltages.

Editing

Using the graphics editor, the limits of the downcast were manually delimited. Any spikes on 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 during quality control.

The pressure ranges over which the bottle samples were taken were logged by manual interaction with the editor. These were subsequently used, in conjunction with a geometrical correction for the position of the water bottles with respect to the CTD pressure transducer, to determine the pressure range of data to be averaged for calibration purposes.

Once screened, the CTD downcasts were loaded into a database under the Oracle relational database management system and later migrated to the National Oceanographic Database.

BODC Quality Control and Calibrations

Pressure

No pressure data logged in air were available for this cruise. However, many of the casts gave negative pressures at the surface. A pressure correction was determined on the basis that the lowest pressure logged at the surface represented zero which gave:

This correction has been applied to the data.

Temperature

The Neil Brown temperatures were in good agreement with digital reversing thermometer readings, hence no temperature calibration was applied.

Salinity

Salinity was calibrated against 23 water bottle samples measured on a Guildline Autosal salinometer. Samples were taken from the bottles fired on five casts. Usually 4-6 samples were taken per cast.

The samples were collected in glass bottles and sealed with plastic stoppers. The temperature at which the samples were measured was 21°C.

The salinity correction determined was:

The salinity signal from two of the casts (03-01 and 18-12) was excessively noisy and the salinity data from these casts have been deleted.

Chlorophyll

An attempt was made to calibrate the fluorometer against chlorophyll measured by HPLC. However, the concentration range of the samples was inadequate to cover the full voltage range, resulting in the calibration being inaccurate for higher chlorophyll concentrations. Instead, the calibration was done against the sum of fluorometrically measured chlorophylls done on size-fractionated samples.

These samples were taken from GoFlo hydrocasts taken within an hour of the CTD casts. The samples were filtered through a membrane filter cascade and extracted in acetone. Chlorophyll was determined on board using a Turner Design bench fluorometer calibrated against absolute chlorophyll standards. The resulting regression equation was:

From graphical examination of the data, the fluorometer was obviously malfunctioning on the casts 03-01, 04-11, 04-46, 04-48, 04-53, 05-13 and 05-46. The chlorophyll data from these casts have been deleted.

Data Reduction

The final data set was produced by binning the calibrated data to 1 (casts shallower than 100 m) or 2 decibars. 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.

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 OMEX3

OMEX3 was one of four fixed stations for the OMEX I project. It was visited by eleven cruises and collected a variety of data during the period June 1993 to October 1995. These include:

• Mooring deployments - Aandeera current meters with transmissometers
• CTD casts
• Net trawls
• Plankton recorders
• Cores
• Water samples

The data collected a site OMEX3 lay within a box bounded by co-ordinates 48° 56.9'N, 013° 42.69'W at the southwest corner and 49° 6.5'N, 013° 17.1'W at the northeast corner, with an approximate depth of 3650 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 OMEX3

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

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