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Metadata Report for BODC Series Reference Number 814108


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Neil Brown MK3 CTD  CTD; water temperature sensor; salinity sensor; dissolved gas sensors
SeaTech transmissometer  transmissometers
Chelsea Technologies Group Aquatracka fluorometer  fluorometers
Chelsea Technologies Group 2-pi PAR irradiance sensor  radiometers
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr Alan Morris
Originating Organization Plymouth Marine Laboratory
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) NSP Plumes Process Study
 

Data Identifiers

Originator's Identifier 1087
BODC Series Reference 814108
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1988-12-22 06:04
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars
 

Spatial Co-ordinates

Latitude 53.55067 N ( 53° 33.0' N )
Longitude 0.10717 E ( 0° 6.4' E )
Positional Uncertainty 0.05 to 0.1 n.miles
Minimum Sensor or Sampling Depth 0.5 m
Maximum Sensor or Sampling Depth 10.41 m
Minimum Sensor or Sampling Height 6.59 m
Maximum Sensor or Sampling Height 16.5 m
Sea Floor Depth 17.0 m
Sea Floor Depth Source -
Sensor or Sampling Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor or Sampling Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
 

Parameters

BODC CODERankUnitsTitle
ATTNZR011per metreAttenuation (red light wavelength) per unit length of the water body by transmissometer
CPHLPR011Milligrams per cubic metreConcentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by in-situ chlorophyll fluorometer
DOXYPR011Micromoles per litreConcentration of oxygen {O2 CAS 7782-44-7} per unit volume of the water body [dissolved plus reactive particulate phase] by in-situ Beckmann probe
IRRDPP011MicroEinsteins per square metre per secondDownwelling 2-pi scalar irradiance as photons of electromagnetic radiation (PAR wavelengths) in the water body by 2-pi scalar radiometer
OXYSBB011PercentSaturation of oxygen {O2 CAS 7782-44-7} in the water body [dissolved plus reactive particulate phase] by in-situ Beckmann probe and computation from concentration using Benson and Krause algorithm
POTMCV011Degrees CelsiusPotential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR011DecibarsPressure (spatial coordinate) exerted by the water body by profiling pressure sensor and correction to read zero at sea level
PSALST011DimensionlessPractical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR011Kilograms per cubic metreSigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST011Degrees CelsiusTemperature of the water body by CTD or STD
TSEDTR011Milligrams per litreConcentration of suspended particulate material {SPM} per unit volume of the water body [particulate >unknown phase] by in-situ optical attenuance measurement and calibration against sample data

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

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.

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 42 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 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).

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 uM (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).

Calibrations

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, 0.002 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, 0.010 PSU, was added to the CTD salinities.

No chlorophyll calibration was possible for this cruise. A best estimate calibration was set up using data from Challenger 41 and Challenger 43. The resulting equation was:

Chlorophyll (mg/m3) = exp (1.277*V - 2.232)

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*0.30 + 228.63 for stations 1059 to 1108
Calibrated oxygen (µM) = Raw oxygen*0.25 + 246.02 for stations 1109 to 1118

No oxygen calibration was possible for stations 1119-1134. All oxygen values in these casts have been set to suspect.

Attenuance was regressed against total 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+0.035)/0.403 (n=27; r2=97.6%)

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

Warnings

The chlorophyll calibration was obtained using data from other cruises.

No dissolved oxygen data are available for casts 1119-1134.

References

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.


Project Information

North Sea Project Plumes Process Study

Estuaries are important boundary sources of some metals and nutrients in the North Sea and distinctive dispersions in their plumes such as the Humber, Wash and Thames outflow, required special study.

Specific objectives included

  • the definition of the spatial and temporal characteristics of the Humber/Wash and Thames by repetitive sampling for selected conservative and non-conservative constituents around a grid enclosing the plume
  • the determination of the transport pathways for non-conservative constituents in relation to suspended particle/water exchanges
  • the characterisation of nutrient and metal transfer across the sediment/water interface

These latter two were carried out through controlled experiments on-board ship. Nutrient flows were correlated with river flows using all available data. A 2-dimensional hydrodynamic model was used to calculate nutrient fluxes and mass balances.


Data Activity or Cruise Information

Cruise

Cruise Name CH42
Departure Date 1988-12-15
Arrival Date 1988-12-29
Principal Scientist(s)Alan W Morris (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
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
Q value below limit of quantification