Metadata Report for BODC Series Reference Number 884303

• 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

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

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 83 CTD Data Documentation

Instrumentation

The CTD profiles were taken with an RVS Neil Brown Systems Mk3B CTD incorporating a pressure sensor, conductivity cell, platinum resistance thermometer and a Beckman dissolved oxygen sensor. The CTD unit was mounted vertically in the centre of a protective cage approximately 1.5 m square. Attached to the bars of the frame was a Chelsea Instruments Aquatracka fluorometer, a Chelsea Instruments Aquatracka configured as a nephelometer and a SeaTech red light (661 nm) transmissometer with a 25 cm path length.

A General Oceanics rosette sampler fitted with 12, 10 litre Niskin or GoFlo bottles was mounted above the frame. The bases of the bottles were 0.75 m above the pressure head with their tops 1.55 m above it.

Lowering rates were generally in the range of 0.5-1.0 m/sec but could be up to 1.5 m/sec. Bottle samples were acquired during the upcast.

Data Acquisition

CTD data were sampled at a frequency of 32 Hz. Data reduction in real time, converting the 32 Hz data to a 1-second time series, was done by the RVS Level A microcomputer system. These were then logged as digital counts by the Level C workstation via the 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 transmissometer and fluorometer, ml/l for oxygen, 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.

Salinity (Practical Salinity Units, as defined by the Practical Salinity Scale (Fofonoff and Millard 1982)) was calculated from the conductivity ratio (conductivity / 42.914) and a time lagged temperature using the function described in UNESCO Report 37 (1981).

The 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 workstation graphics editor. In addition to reformatting, the transfer program applied the following modifications to the data:

Dissolved oxygen was converted from ml/l to µM by multiplying the values by 44.66.

The raw transmissometer voltages were corrected for light source decay using a correction ratio computed from light reading in air taken during the cruise (4.675V) and the manufacturer's figure for the new instrument (4.738V). Transmissometer voltages were converted to percentage transmission by multiplying them by 20 and then to attenuance by applying the formula:

The nominal calibration applied to the fluorometer was removed.

Editing

The reformatted CTD data were transferred onto a high speed graphics workstation. Using a custom in-house graphics editor, the downcasts were manually delimited and any spikes flagged suspect.

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

Visual inspection showed that the attenuance data from this cruise had severe problems. There was a strong hysteresis between the up and downcasts and clear water values were drifting from cast to cast anywhere between 0.5 and 1.0 per m. Consequently, these data have been discarded.

Calibration

Pressure

The pressure offset was determined by looking at the pressures recorded when the CTD was clearly logging in air (readily apparent from the conductivity channel). No pressure correction proved necessary.

Temperature

Since no reversing thermometer readings were available for this cruise the offset has been taken to be zero. The instrument was calibrated in the RVS base facility just prior to the cruise and experience from previous cruises has shown the Neil Brown Mk3 thermometer to be a very stable and accurate instrument.

Salinity

The data originator determined that the CTD was reading 0.078 PSU low when compared with salinometer determinations on bottle samples. This correction has been applied to the data.

Oxygen

The dissolved oxygen sensor was calibrated by the data originator against water bottle samples analysed following the Winkler titration procedures. The calibration obtained was:

This has been applied to the data. Note the intercept has been adjusted from the value in the cruise report to allow for the conversion from ml/l to µM.

Chlorophyll

A calibration was done against 87 fluorometrically assayed, extracted chlorophyll samples. The resulting equation was:

This has been applied to the data.

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.

Oxygen saturations were calculated using the algorithm of Benson and Krause (1984).

References

Benson, B.B. and Krause D. jnr., 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.

Fofonoff, N.P. and Millard, R.C., 1982. Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science, 44.

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: