Metadata Report for BODC Series Reference Number 792977
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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.
These specification apply to the MK3C version.
3200 m (optional)
|-3 to 32°C||1 to 6.5 S cm-1|
0.03% FS < 1 msec
0.003°C < 30 msec
0.0001 S cm-1
0.0003 S cm-1 < 30 msec
Further details can be found in the specification sheet.
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.
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.
- 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)
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.
RRS Challenger 47 CTD Data Documentation
The CTD unit was a Neil Brown Mk. 3 incorporating a pressure sensor, conductivity cell, platinum resistance thermometer and a Beckmann dissolved oxygen sensor. This was mounted vertically in the centre of a protective cage approximately 1.5m square.
Attached to bars of the frame were an Aquatracka logarithmic response fluorometer and a Seatech red light (661 nm) transmissometer with a 25 cm path length.
Above the frame was a General Oceanics rosette sampler fitted with 12, 10 litre water bottles. These comprised a mixture of Niskin, general purpose Go-Flo and ultra-clean teflon lined Go-Flo bottles as dictated by sampling requirements. The base of the bottles were 0.75m above and the tops 1.55m above the pressure head. One bottle was fitted with a holder for twin reversing thermometers mounted 1.38m above the CTD temperature sensor.
Above the rosette was a PML 2-pi PAR (photosynthetically active radiation) sensor pointing upwards to measure downwelling irradiance. A second 2-pi PAR sensor, pointing downwards, was fitted to the bottom of the cage to measure upwelling irradiance. It should be noted that these sensors were vertically separated by 2m with the upwelling sensor 0.2m below the pressure head and the downwelling sensor 1.75m above it.
No account has been taken of rig geometry in the compilation of the CTD data set. However, all water bottle sampling depths have been corrected for rig geometry and represent the true position of the midpoint of the water bottle in the water column.
Operational procedure and data logging
On each cast the CTD was lowered to a depth of approximately 5 metres and held until the oxygen reading stabilised. It was then raised to the surface and lowered continuously at 0.5 to 1 m/s to as close as possible to the sea floor. The upcast was done in stages between the bottle firing depths.
Data were logged by the Research Vessel Services ABC data logging system. The deck unit outputs were sampled at 32 Hz by a microprocessor interface (the Level A) which passed time stamped averaged cycles at 1 Hz to a Sun workstation (the Level C) via a buffering system (the Level B).
The raw data comprised ADC counts. These were converted into engineering units (Volts for PAR meters, fluorometer and transmissometer: ml/l for oxygen: mmho/cm for conductivity: °C for temperature) by the application of laboratory determined calibrations and salinity was computed using the algorithm in Fofonoff and Millard (1983). The data were submitted to BODC in this form.
Within BODC the data were reformatted on an IBM main-frame. At this stage transmissometer air readings recorded during the cruise were used to correct the transmissometer voltage to the manufacturer's specified voltage by ratio. The voltages were then converted to percentage transmittance (multiplied by 20.0) and dissolved oxygen converted to µM (multiplied by 44.66).
Next the data were loaded onto a Silicon Graphics workstation. A sophisticated interactive screening program was used to delimit the downcast, mark the depth range of water bottle firings and flag any spikes on all of the data channels.
The data were returned to the IBM and the downcasts loaded into a database under the Oracle relational database management system. At this stage percentage transmittance was converted to attenuance to eliminate the influence of instrument path length using the equation:
|Attenuance = -4.0 * loge (% trans/100)|
Calibration sample data were merged into the database and files of sample value against CTD reading at the bottle depth were prepared for the Principal Investigators to determine the calibrations. Due allowance was made for rig geometry. Note that CTD downcast values were generally used although the bottles were fired on the upcast. The validity of an assumed static water column for the duration of the cast was checked on the graphics workstation and upcast values substituted if necessary.
Sigma-T values were calculated using the algorithm presented in Fofonoff and Millard (1983). Oxygen saturations were computed using the equation of Weiss (1970).
For each cast the mean pressure reading logged whilst the instrument was in air was determined. The average of these, determined as -1.9 db, was added to each pressure value.
Two digital reversing thermometers were fired at the bottom of each cast. The mean difference, determined for all casts on the cruise, between the averaged calibrated readings and the CTD temperature, 0.005 °C, was added to the CTD temperatures.
A sample was taken from the bottom bottle of each cast and salinity was determined using a Guildline Autosal. The mean difference, determined for all casts on the cruise, between the bottle values and the CTD salinity, 0.027 PSU, was added to the CTD salinities.
Extracted chlorophyll values were log transformed and regressed against fluorometer voltages to give the calibration equation:
|Chlorophyll (mg/m3) = exp (1.211*V - 2.168) (n=296; r2=27.35)|
Dissolved oxygen was calibrated against Winkler titration data for water bottle samples as a primary standard and calibrated data from the underway Endeco system as a secondary standard.
The resulting calibration equations were:
|Calibrated oxygen (µM) = Raw oxygen*0.39 + 205.99 for stations 1463 to 1474|
|Calibrated oxygen (µM) = Raw oxygen*0.46 + 179.60 for stations 1475 to 1543|
All dissolved oxygen data for stations with no calibrations defined (1450-1462, 1544-1584) have been flagged as suspect.
Attenuance was regressed against total, organic and inorganic suspended matter determinations to derive the equations below to allow attenuance to be expressed in terms of suspended matter.
|Total suspended matter (mg/l) = (Attenuance-0.488)/0.283 (n=297; r2=92.6%)|
|Inorganic suspended matter (mg/l) = (Attenuance-0.603)/0.293 (n=295; r2=92.6%)|
|Organic suspended matter (mg/l) = (Attenuance+0.073)/2.961 (n=295; r2=82.6%)|
The PAR meters were calibrated using the following laboratory determined calibrations:
|Upwelling:||PAR (µE/m2/s) = exp (-5.151*V + 6.6035) * 0.0375|
|Downwelling:||PAR (µE/m2/s) = exp (-5.122*V + 6.5739) * 0.0375|
The statistics for the chlorophyll calibration are poor.
No oxygen calibration was possible for a number of stations at the start and end of the cruise. All affected data have been flagged suspect.
Fofonoff, N.P and Millard, R.C. Jr. (1983). Algorithms for the computation of fundamental properties of sea water.
Weiss, R.F. (1970). The solubility of nitrogen, oxygen and argon in water and sea water. Deep Sea Res. 17, 721-735.
North Sea Project
The North Sea Project (NSP) was the first Marine Sciences Community Research project of the Natural Environment Research Council (NERC). It evolved from a NERC review of shelf sea research, which identified the need for a concerted multidisciplinary study of circulation, transport and production.
The ultimate aim of the NERC North Sea Project was the development of a suite of prognostic water quality models to aid management of the North Sea. To progress towards water quality models, three intermediate objectives were pursued in parallel:
- Production of a 3-D transport model for any conservative passive constituent, incorporating improved representations of the necessary physics - hydrodynamics and dispersion;
- Identifying and quantifying non-conservative processes - sources and sinks determining the cycling and fate of individual constituents;
- Defining a complete seasonal cycle as a database for all the observational studies needed to formulate, drive and test models.
Proudman Oceanographic Laboratory hosted the project, which involved over 200 scientists and support staff from NERC and other Government funded laboratories, as well as seven universities and polytechnics.
The project ran from 1987 to 1992, with marine field data collection between April 1988 and October 1989. One shakedown (CH28) and fifteen survey cruises (Table 1), each lasting 12 days and following the same track, were repeated monthly. The track selected covered the summer-stratified waters of the north and the homogeneous waters in the Southern Bight in about equal lengths together with their separating frontal band from Flamborough head to Dogger Bank, the Friesian Islands and the German Bight. Mooring stations were maintained at six sites for the duration of the project.
|Table 1: Details of NSP Survey Cruises on RRS Challenger|
|CH28||29/04/88 - 15/05/88|
|CH33||04/08/88 - 16/08/88|
|CH35||03/09/88 - 15/09/88|
|CH37||02/10/88 - 14/10/88|
|CH39||01/11/88 - 13/11/88|
|CH41||01/12/88 - 13/12/88|
|CH43||30/12/88 - 12/01/89|
|CH45||28/01/89 - 10/02/89|
|CH47||27/02/89 - 12/03/89|
|CH49||29/03/89 - 10/04/89|
|CH51||27/04/89 - 09/05/89|
|CH53||26/05/89 - 07/06/89|
|CH55||24/06/89 - 07/07/89|
|CH57||24/07/89 - 06/08/89|
|CH59||23/08/89 - 04/09/89|
|CH61||21/09/89 - 03/10/89|
Alternating with the survey cruises were process study cruises (Table 2), which investigated some particular aspect of the science of the North Sea. These included fronts (nearshore, circulation and mixing), sandwaves and sandbanks, plumes (Humber, Wash, Thames and Rhine), resuspension, air-sea exchange, primary productivity and blooms/chemistry.
|Table 2: Details of NSP Process cruises on RRS Challenger|
|CH34||18/08/88 - 01/09/88||Fronts - nearshore|
|CH36||16/09/88 - 30/09/88||Fronts - mixing|
|CH56||08/07/89 - 22/07/89||Fronts - circulation|
|CH58||07/08/89 - 21/08/89||Fronts - mixing|
|CH38||24/10/88 - 31/10/88||Sandwaves|
|CH40||15/11/88 - 29/11/88||Sandbanks|
|CH42||15/12/88 - 29/12/88||Plumes/Sandbanks|
|CH46||12/02/89 - 26/02/89||Plumes/Sandwaves|
|CH44||13/01/89 - 27/01/89||Resuspension|
|CH52||11/05/89 - 24/05/89||Resuspension|
|CH60||06/09/89 - 19/09/89||Resuspension|
|CH48||13/03/89 - 27/03/89||Air/sea exchanges|
|CH62||05/10/89 - 19/10/89||Air/sea exchanges|
|CH50||12/04/89 - 25/04/89||Blooms/chemistry|
|CH54||09/06/89 - 22/06/89||Production|
In addition to the main data collection period, a series of cruises took place between October 1989 and October 1990 that followed up work done on previous cruises (Table 3). Process studies relating to blooms, plumes (Humber, Wash and Rhine), sandwaves and the flux of contaminants through the Dover Strait were carried out as well as two `survey' cruises.
|Table 3: Details of NSP `Follow up' cruises on RRS Challenger|
|CH62A||23/10/89 - 03/11/89||Blooms|
|CH64||03/04/90 - 03/05/90||Blooms|
|CH65||06/05/90 - 17/05/90||Humber plume|
|CH66A||20/05/90 - 31/05/90||Survey|
|CH66B||03/06/90 - 18/06/90||Contaminants through Dover Strait|
|CH69||26/07/90 - 07/08/90||Resuspension/Plumes|
|CH72A||20/09/90 - 02/10/90||Survey|
|CH72B||04/10/90 - 06/10/90||Sandwaves/STABLE|
|CH72C||06/10/90 - 19/10/90||Rhine plume|
The data collected during the observational phase of the North Sea Project comprised one of the most detailed sets of observations ever undertaken in any shallow shelf sea at that time.
|Principal Scientist(s)||Peter Liss (University of East Anglia School of Environmental Sciences)|
Complete Cruise Metadata Report is available here
Fixed Station Information
|Station Name||NSP CTD Site CN|
|Latitude||55° 29.92' N|
|Longitude||3° 45.48' E|
|Water depth below MSL|
North Sea Project CTD Site CN
Site CN was one of 123 North Sea Project CTD fixed stations.
Casts were performed by 11 cruises between 11/08/1988 and 29/09/1990, the measurements collected lie within a box bounded by co-ordinates 55.49312°N, 3.72972°E at the southwest corner and 55.50426°N, 3.78619°E at the northeast corner.
Related Fixed Station activities are detailed in Appendix 1
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||Below detection limit|
|>||In excess of quoted value|
|A||Taxonomic flag for affinis (aff.)|
|B||Beginning of CTD Down/Up Cast|
|C||Taxonomic flag for confer (cf.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|I||Taxonomic flag for single species (sp.)|
|K||Improbable value - unknown quality control source|
|L||Improbable value - originator's quality control|
|M||Improbable value - BODC quality control|
|O||Improbable value - user quality control|
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|
Appendix 1: NSP CTD Site CN
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.
|Series Identifier||Data Category||Start date/time||Start position||Cruise|
|769618||CTD or STD cast||1988-08-11 15:24:00||55.4995 N, 3.7495 E||RRS Challenger CH33|
|783728||CTD or STD cast||1988-09-10 07:20:00||55.49983 N, 3.74817 E||RRS Challenger CH35|
|821941||CTD or STD cast||1988-11-07 22:46:00||55.4965 N, 3.75717 E||RRS Challenger CH39|
|786935||CTD or STD cast||1989-01-10 10:38:00||55.49583 N, 3.75533 E||RRS Challenger CH43|
|1857733||Water sample data||1989-03-06 05:35:00||55.50418 N, 3.78619 E||RRS Challenger CH47|
|792989||CTD or STD cast||1989-03-06 05:49:00||55.50433 N, 3.78517 E||RRS Challenger CH47|
|795348||CTD or STD cast||1989-05-04 06:11:00||55.5005 N, 3.7515 E||RRS Challenger CH51|
|1861178||Water sample data||1989-05-04 06:16:00||55.50049 N, 3.75142 E||RRS Challenger CH51|
|796708||CTD or STD cast||1989-06-02 01:34:00||55.49317 N, 3.74867 E||RRS Challenger CH53|
|1863726||Water sample data||1989-06-02 01:38:00||55.49312 N, 3.7487 E||RRS Challenger CH53|
|801896||CTD or STD cast||1989-08-30 02:32:00||55.5015 N, 3.72967 E||RRS Challenger CH59|
|1856594||Water sample data||1989-08-30 02:36:00||55.50146 N, 3.72972 E||RRS Challenger CH59|
|800543||CTD or STD cast||1989-09-28 14:38:00||55.50033 N, 3.74683 E||RRS Challenger CH61|
|1855321||Water sample data||1989-09-28 14:41:00||55.50032 N, 3.74691 E||RRS Challenger CH61|
|803252||CTD or STD cast||1990-05-28 05:44:00||55.5005 N, 3.74867 E||RRS Challenger CH66A|
|805050||CTD or STD cast||1990-09-29 17:51:00||55.49917 N, 3.74967 E||RRS Challenger CH72A|