Metadata Report for BODC Series Reference Number 823161
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
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Problem Reports
Due to a data processing error the accuracy of the temperature and salinity data has been reduced by an order of magnitude. The data should not be used for any purpose requiring temperature or salinity accuracy better than 0.2.
Data Access Policy
Open 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.
If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:
"Contains public sector information licensed under the Open Government Licence v1.0."
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.
Pressure | Temperature | Conductivity | |
Range | 6500 m 3200 m (optional) | -3 to 32°C | 1 to 6.5 S cm-1 |
Accuracy | 0.0015% FS 0.03% FS < 1 msec | 0.0005°C 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.
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.
Chelsea Technologies Photosynthetically Active Radiation (PAR) Irradiance Sensor
This sensor was originally designed to assist the study of marine photosynthesis. With the use of logarithmic amplication, the sensor covers a range of 6 orders of magnitude, which avoids setting up the sensor range for the expected signal level for different ambient conditions.
The sensor consists of a hollow PTFE 2-pi collector supported by a clear acetal dome diverting light to a filter and photodiode from which a cosine response is obtained. The sensor can be used in moorings, profiling or deployed in towed vehicles and can measure both upwelling and downwelling light.
Specifications
Operation depth | 1000 m |
Range | 2000 to 0.002 µE m-2 s-1 |
Angular Detection Range | ± 130° from normal incidence |
Relative Spectral Sensitivity | flat to ± 3% from 450 to 700 nm down 8% of 400 nm and 36% at 350 nm |
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.
RRS Challenger 64 CTD Data Documentation
Instrumentation
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, 1.75m above the pressure head, was a PML 2-pi PAR (photosynthetically active radiation) sensor pointing upwards to measure downwelling irradiance. For the first few casts (2924-2930) a second PAR meter was fitted pointing downwards 0.2m below the pressure head to measure upwelling irradiance.
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).
Data processing
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).
Calibrations
For each cast the mean pressure reading logged whilst the instrument was in air was determined. The average of these, determined as -0.9 db, was added to each pressure value.
Temperature and salinity were affected by a data processing error and no resources were available to rework the data from the raw state. Rather than reject the data, the effects of the error have been minimised by using a modified calibration procedure.
The bottle firing reports include the temperature and salinity logged by a microcomputer free from the processing error. These were calibrated against reversing thermometer and water bottle data to provide a secondary standard with several readings per cast. The best mean salinity and temperature offsets for small groups of casts were determined to be:
Start | End | Temperature | Salinity |
---|---|---|---|
2924 | 2924 | -0.002 | -0.163 |
2925 | 2929 | -0.116 | 0.142 |
2930 | 2951 | -0.352 | 0.376 |
2952 | 2955 | -0.437 | 0.437 |
2956 | 2973 | -0.389 | 0.399 |
The offset at the top and bottom of each cast was checked and if the drift within cast were excessive the affected portions of the cast were flagged suspect. The net result is that the accuracy of the temperature and salinity measurements is reduced by an order of magnitude.
Extracted chlorophyll values were log transformed and regressed against fluorometer voltages to give the calibration equation:
Chlorophyll (mg/m3) = exp (1.850*V - 3.470) (n=91; r2=73.5%) |
There were no dissolved oxygen calibration samples taken on this cruise. All dissolved oxygen values have been flagged as suspect as a result.
Attenuance was regressed against total suspended matter determinations to derive the equation below to allow attenuance to be expressed in terms of suspended matter.
Total suspended matter (mg/l) = (Attenuance-0.391)/0.239 (n=88; r2=69.4%) |
A problem was encountered with the PAR meters. These were tested to a pressure of 300 db. Unfortunately, on cast 2930 the meters were left on the rig on a deep cast and they imploded. The downwelling sensor was replaced by a spare unit but no spare was available to replace the upwelling sensor.
The following laboratory calibrations were applied:
Casts 2924 to 2930
Upwelling: | PAR (µE/m2/s) = exp (-5.122*V + 6.5739) * 0.0375 |
Downwelling: | PAR (µE/m2/s) = exp (-5.139*V + 6.5506) * 0.0375 |
Casts 2931 to 2973
Downwelling: PAR (µE/m2/s) = exp (-5.247*V + 6.7806) * 0.0375 |
Warnings
Due to a data processing error the accuracy of the temperature and salinity data has been reduced by an order of magnitude. The data should not be used for any purpose requiring temperature or salinity accuracy better than 0.2.
No dissolved oxygen data are available as no calibrations were done.
References
Fofonoff, N.P and Millard, R.C. Jr. (1983). Algorithms for the computation of fundamental properties of sea water.
Project Information
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 | |
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Cruise No. | Date |
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 | ||
---|---|---|
Cruise No. | Date | Process |
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 | ||
---|---|---|
Cruise No. | Date | Process |
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.
North Sea Project Blooms/Chemistry Process Study
This study examined the effects of developing phytoplankton blooms on water chemistry. Time series measurements using drogued buoys (primary production, dimethyl sulphide and vertical fluxes) were recorded on a diatom bloom off the North Yorkshire coast and a Phaeocystis bloom in the Southern Bight. The aim was
- to investigate gross and net primary production during bloom conditions
- to examine the relationships between primary productivity and biogeochemical cycling of certain trace metals and biogenic traces gases
Data Activity or Cruise Information
Cruise
Cruise Name | CH64 |
Departure Date | 1990-04-03 |
Arrival Date | 1990-05-03 |
Principal Scientist(s) | Nicholas J P Owens (Plymouth Marine Laboratory) |
Ship | RRS Challenger |
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:
Flag | Description |
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Blank | Unqualified |
< | 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.) |
D | Thermometric depth |
E | End of CTD Down/Up Cast |
G | Non-taxonomic biological characteristic uncertainty |
H | Extrapolated value |
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 |
N | Null value |
O | Improbable value - user quality control |
P | Trace/calm |
Q | Indeterminate |
R | Replacement value |
S | Estimated value |
T | Interpolated value |
U | Uncalibrated |
W | Control value |
X | Excessive difference |
SeaDataNet Quality Control Flags
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
Flag | Description |
---|---|
0 | no quality control |
1 | good value |
2 | probably good value |
3 | probably bad value |
4 | bad value |
5 | changed value |
6 | value below detection |
7 | value in excess |
8 | interpolated value |
9 | missing value |
A | value phenomenon uncertain |
B | nominal value |
Q | value below limit of quantification |