Metadata Report for BODC Series Reference Number 958856


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
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr Roger Harris
Originating Organization Plymouth Marine Laboratory
Processing Status banked
Project(s) BOFS
Joint Global Ocean Flux Study (JGOFS)
 

Data Identifiers

Originator's Identifier 61/201#7
BODC Series Reference 958856
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1991-07-20 11:12
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 2.0 decibars
 

Spatial Co-ordinates

Latitude 61.05283 N ( 61° 3.2' N )
Longitude 19.74850 W ( 19° 44.9' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth 0.99 m
Maximum Sensor Depth 301.88 m
Minimum Sensor Height 2125.42 m
Maximum Sensor Height 2426.31 m
Sea Floor Depth 2427.3 m
Sensor Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor 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 CODE Rank Units Short Title Title
ATTNZR01 1 per metre Atten_red Attenuation (red light wavelength) per unit length of the water body by transmissometer
CPHLPR01 1 Milligrams per cubic metre chl-a_water_ISfluor Concentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by in-situ chlorophyll fluorometer
DOXYPR01 1 Micromoles per litre WC_dissO2_Beck Concentration of oxygen {O2 CAS 7782-44-7} per unit volume of the water body [dissolved plus reactive particulate phase] by in-situ Beckmann probe
IRRDPP01 1 MicroEinsteins per square metre per second DwIrr_2-piPAR Downwelling 2-pi scalar irradiance as photons (PAR wavelengths) in the water body by 2-pi scalar radiometer
IRRUPP01 1 MicroEinsteins per square metre per second UwIrr_2-piPAR Upwelling 2-pi scalar irradiance as photons (PAR wavelengths) in the water body by 2-pi scalar radiometer
OXYSBB01 1 Percent BKBeck Saturation 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
POATCV01 1 per metre PotAtten Potential attenuance (unspecified wavelength) per unit length of the water body by transmissometer and computation using P-EXEC algorithm
POTMCV01 1 Degrees Celsius WC_Potemp Potential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR01 1 Decibars Pres_Z Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level
PSALST01 1 Dimensionless P_sal_CTD Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR01 1 Kilograms per cubic metre SigTheta Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST01 1 Degrees Celsius WC_temp_CTD Temperature of the water body by CTD or STD
 

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 .

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

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 Charles Darwin 61 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 Beckmann dissolved oxygen sensor. This was mounted vertically in the centre of a protective cage approximately 1.5m square.

Attached to the bars of the frame were a Chelsea Instruments Aquatracka fluorometer, and a SeaTech red light (661nm) transmissometer with a 25cm path length.

Above the frame was a General Oceanics rosette sampler fitted with 12, 10 litre Niskin bottles. The bases of the bottles were 0.75m above the pressure head with their tops 1.55m above it. One of the bottles was fitted with a holder for up to three digital reversing thermometers mounted 1.38m above the CTD temperature sensor. On deep casts, a second bottle was sometimes similarly equipped.

Above the rosette was a PML 2-pi PAR (photosynthetically available radiation) sensor pointing upwards to measure downwelling irradiance. A second such sensor was fitted to the bottom of the cage facing downwards to measure upwelling irradiance. Both instruments were pressure hardened to 1000 db. It should be noted that the PAR meters were vertically separated by approximately 2m.

Lowering rates of up to 1.5 m/sec were used, although rates were generally in the range 0.5 - 1 m/sec. Bottle samples and reversing thermometer measurements were acquired on the ascent of each cast.

Data Acquisition

CTD data were sampled at a frequency of 32 Hz. Data reduction was in real time, converting the 32 Hz data to a 1-second time-series (done by the RVS Level A system) which was then passed through an Analogue-Digital Converter and logged as digital counts on the Level C.

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 PAR meters, fluorometer and transmissometer: ml/l for oxygen: mmho/cm for conductivity: °C for temperature).

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

Data were written onto magnetic tape in GF3 format and submitted to BODC.

Post-Cruise Processing

Reformatting

The data were converted into the BODC internal format (PXF) 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 readings in air taken during the cruise (4.800V) and the manufacturer's figure for the new instrument (4.807V). Transmissometer voltages were converted to percentage transmission by multiplying them by 20.

The 2-pi PAR data were converted from Volts to µE/m 2 /s using the equations:

Downwelling: PAR = exp(-4.977*V + 7.0040) * 0.0375
Upwelling : PAR = exp(-5.031*V + 6.8751) * 0.0375

Editing

Reformatted CTD data were transferred onto a high-speed graphics workstation. A number of tasks was performed here, using an in-house graphics editor. Initially, downcasts and upcasts were differentiated and the limits of the downcast were manually flagged.

Secondly, spikes on the downcast data were manually flagged. No data values were edited or deleted; flagging was achieved by modification of the associated quality control character flags.

Finally, the pressure ranges over which bottle samples were being collected, were logged by manual interaction with the software. Usually, the marked reaction of the oxygen sensor to the bottle firing sequence was used to determine this.

These pressure ranges 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 values.

Once screened on the workstation, the CTD downcasts were loaded into a database under the Oracle relational database management system. During the loading process, the transmissometer data were converted to attenuance using the algorithm:

attenuance = -4.0 * ln (percent transmittance / 100.0)

Calibration

With the exception of pressure, calibrations were done by comparison of CTD data against measurements made on water bottle samples or from reversing thermometers mounted on the water bottles. In general, values were averaged from the CTD downcasts (most casts were shallow; therefore hysteresis is assumed to be negligible). Where inspection on a graphics workstation showed significant hysteresis, values were manually extracted from the CTD upcasts.

All calibrations described here have been applied to the data.

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). For this cruise, considerable drift was detected in the pressure value in air. Consequently, the casts were grouped on the basis of pressure in air to give the following pressure corrections:

CTD 61/192#1 (11/07/1991) to CTD 61/195#3 (14/07/1991): Pcorr = Pobs - 0.19
CTD 61/195#4 (14/07/1991) to CTD 61/204#3 (23/07/1991): Pcorr = Pobs - 0.83
CTD 61/204#4 (23/07/1991) to CTD 61/205#12 (24/07/1991): Pcorr = Pobs - 1.27
Temperature

The CTD temperature sensor was calibrated against deep sea digital reversing thermometers (type RTM 4002 with manufacturer's calibrations applied).

Tcorr = Tobs - 0.004
Salinity

Salinity was calibrated against water bottle samples measured on the Guildline 55358 Autolab Salinometer during the cruise. Samples were generally taken from the first bottle fired on each cast which would normally be at the maximum depth sampled. On some deep casts, one or even two additional samples were taken spaced through the water column.

Samples were collected in glass bottles filled to just below the neck and sealed with plastic stoppers. Batches of samples were left for at least 24 hours to reach thermal equilibrium in the constant temperature laboratory containing the salinometer before analysis.

The correction determined for this cruise was:

Scorr = Sobs + 0.018
Oxygen

The dissolved oxygen sensor was calibrated against samples analysed following the Winkler titration procedures outlined in Carpenter (1965) and Williams and Jenkinson (1982). The values were quoted in µmol/kg and were converted to µM at in-situ temperature using densities calculated from the calibrated CTD data. The probe appeared relatively stable and a single calibration equation was determined for the whole cruise:

Ocorr = Oobs*0.45 + 158.0

Oxygen saturations present in the data files were computed using the algorithm presented in Benson and Krause (1984).

Chlorophyll

The fluorometer was calibrated in terms of chlorophyll using a regression technique against extracted chlorophyll. Samples were taken from each water bottle, filtered and extracted into acetone. Chlorophyll was determined using a Turner Designs bench fluorometer calibrated against absolute chlorophyll standards.

Initially, calibration was attempted using multiple regression including a PAR term. However, only three of the calibration samples were collected at light levels in excess of 80 µE/m 2 /s and the resulting calibration when extrapolated to higher light levels resulted in ludicrously high chlorophyll values. Consequently, the light term was omitted. The relatively small number of samples (50) forced the treatment of the whole cruise as a single population.

The calibration equation determined was

Chlorophyll (mg/m 2 ) = exp (V*2.20 - 4.71) (r2=38.2%)

The statistics of this calibration are comparatively poor and hence the absolute chlorophyll values should be used with caution.

Binning

The CTD data present on the CD-ROM have been binned by averaging over 1 db intervals for casts shallower than 100m and 2 db intervals for casts deeper than 100m. The binning algorithm only included data values associated with good flags. If no good data were available for a bin, linear interpolation was used to fill gaps of up to 3 bins. Gaps larger than this were left null.

The result of this algorithm is that data points are either considered good, in which case there is a value, or null, in which case the field is left blank. This removes the need for quality control flags which are often ignored and consequently make the data much easier to handle. The disadvantage is that some information is lost. The full resolution data have been archived by BODC and may be obtained on request.

Quality Control

Normal practice is to compare the theta/salinity relationship for deep casts against the canonical relationship for North Atlantic deep waters described by Saunders and Manning (1984) and given in Saunders (1986). However, no suitable deep casts were done on this cruise (the deepest was to approximately 2700 m) and hence no comparison was possible.

Previous experience of the calibration procedures on BOFS cruises, where no attempt is made to tune the thermal lag correction and the number of calibration samples is limited has shown an accuracy in salinity of 0.01 to 0.02 PSU. There is no reason to believe that the data from this cruise are any better than this. Consequently, usage of the data for purposes where high accuracy salinity data are required is not recommended.

Data Warnings

Salinity accuracy is not known but is believed to be no better than 0.01 PSU and may possible be as low as 0.02.

The chlorophyll calibration is weak.

References

BENSON B.B., KRAUSE D. Jr. 1984. The concentration and isotopic fractionation of oxygen dissolved in fresh water and sea water in equilibrium with the atmosphere. Limnol. Oceanogr. 29: 620-632.

CARPENTER J.H. 1965. The Chesapeake Bay Institute techniques for the Winkler dissolved oxygen method. Limnology and Oceanography 10 : 141-143.

FOFONOFF N.P., MILLARD R.C. 1982. Algorithms for computation of fundamental properties of seawater. UNESCO Technical papers in Marine Science 44.

SAUNDERS P.M., MANNING A. 1984. CTD Data from the Northeast Atlantic Ocean, 22N-33N, 19-24W, July 1983 during RRS Discovery cruises 138,139. IOS Deacon Laboratory technical report 188.

SAUNDERS P.M. 1986. CTD data from the Madeira and Iberian abyssal plains, Charles Darwin cruises 3/85 and 9A/85. IOS Deacon Laboratory technical report 227.

UNESCO 1981. Background papers and supporting data on the Practical Salinity Scale, 1978. Unesco Technical Papers in Marine Science 37 144pp.

WILLIAMS P. J. leB., JENKINSON N.W. 1982. A transportable microprocessor-controlled precise Winkler titration suitable for field station and shipboard use. Limnol. Oceanogr. 27 : 567-585.


Project Information

Biogeochemical Ocean Flux Study (BOFS)

The Biogeochemical Ocean Flux Study (BOFS) was a Community Research Project within the Marine and Atmospheric Sciences Directorate (MASD) of the Natural Environment Research Council. The project provided a major United Kingdom contribution to the international Joint Global Ocean Flux Study (JGOFS). The project ran from April 1987 until March 1992 but was extended through bridging funds until March 1993. The BOFS North Atlantic Data Set was collected during the initial five year period. Fieldwork in the bridging year focused on the Antarctic in late 1992. These data will form part of a subsequent electronic publication of Antarctic data and are not included on this CD-ROM.

The primary aims of the BOFS programme were:

A Community Research Project brings together scientists from NERC institutes and UK universities to work on a common problem. In this way resources far beyond the scope of individual research groups may be brought to bear on a common problem. The project is coordinated through a host laboratory which has responsibility for financial management, organisation and logistics. The host laboratory for BOFS was the Plymouth Marine Laboratory (PML).

Fieldwork

The BOFS North Atlantic data set was the result of fieldwork carried out on 11 research cruises. Four studies were carried out during three field seasons in 1989, 1990 and 1991; the 1989 North Atlantic Bloom Experiment, the 1990 Lagrangian Experiment, the 1990 BOFS Benthic Study and the 1991 Coccolithphore Study. Measurements taken include:

Physical (e.g. temperature, salinity and optics)
Meteorology and positioning
Chemical (e.g. dissolved oxygen, organic carbon and nitrogen)
Biological (e.g. biomass, pigments and bacteria production)
Geological (sediment traps)

The Sterna 1992 project (the Southern Ocean component of BOFS) aimed to measure the size and variability of carbon and nitrogen fluxes during early summer in the Southern Ocean, with particular emphasis on rates and processes in the marginal ice zone. Fieldwork was carried out between October and December 1992 in the Southern Ocean area, approximately 55°S to 70°S, 60°W to 85°W. A wide range of physical, chemical and biological parameters were measured.

Data Management

Data management services to BOFS were provided by the British Oceanographic Data Centre, funded by the UK Natural Environment Research Council.


Joint Global Ocean Flux Study (JGOFS)

JGOFS was an international and multi-disciplinary programme, which ran from February 1987 to December 2003, with participants from more than 20 nations. JGOFS was launched at a planning meeting in Paris under the auspices of the Scientific Committee of Oceanic Research (SCOR), a committee of the International Council for Science (ICSU) and later became one of the first core projects of the International Geosphere-Biosphere Programme (IGBP) in 1989.

The primary aims of the JGOFS programme were:

JGOFS consisted of fieldwork, synthesis and modelling phases. Further information about JGOFS may be found at the international Joint Global Ocean Flux Study web site.

JGOFS fieldwork

Date Fieldwork
1988 - 1990 Long-term time series stations established near Bermuda, Hawaii and in the Ligurian Sea
1989 - 1991 North Atlantic Bloom Experiment (NABE)
1991 - 1994 Equatorial Pacific Process Study
1992 - 1998 Southern Ocean Process Study
1994 - 1995 Indian Ocean (Arabian Sea) Process Study
1998 North Pacific Process Study

Synthesis and modelling phase

From 1998, as the fieldwork for most process studies were being completed, JGOFS focused on:

  1. Integrating regional synthesis and modelling activities
  2. Maintaining links to other ocean observing and global change programmes
  3. Developing a global synthesis and modelling phase

Data availability

The field data collected during JGOFS has been published on two DVDs. These are available via the World Data Center for Oceanography, Silver Spring and are entitled:

Data sets making up the UK contribution to JGOFS, for which BODC provided data management support, are also available directly from BODC.


Data Activity or Cruise Information

Cruise

Cruise Name CD61
Departure Date 1991-07-06
Arrival Date 1991-07-29
Principal Scientist(s)Roger Harris (Plymouth Marine Laboratory)
Ship RRS Charles Darwin

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