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Metadata Report for BODC Series Reference Number 1203869


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Sea-Bird SBE 43 Dissolved Oxygen Sensor  dissolved gas sensors
Sea-Bird SBE 911plus CTD  CTD; water temperature sensor; salinity sensor
WETLabs ECO BB(RT)D Scattering Meter  optical backscatter sensors
Sea-Bird SBE 3plus (SBE 3P) temperature sensor  water temperature sensor
Sea-Bird SBE 4C conductivity sensor  salinity sensor
Chelsea Technologies Group Aquatracka III fluorometer  fluorometers
Chelsea Technologies Group Alphatracka II transmissometer  transmissometers
Instrument Mounting lowered unmanned submersible
Originating Country United Kingdom
Originator Mr Colin Griffiths
Originating Organization Scottish Association for Marine Science
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) -
 

Data Identifiers

Originator's Identifier D379_061
BODC Series Reference 1203869
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2012-08-08 22:09
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 2.0 decibars
 

Spatial Co-ordinates

Latitude 59.10007 N ( 59° 6.0' N )
Longitude 14.31525 W ( 14° 18.9' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor or Sampling Depth 1.98 m
Maximum Sensor or Sampling Depth 741.64 m
Minimum Sensor or Sampling Height 7.36 m
Maximum Sensor or Sampling Height 747.02 m
Sea Floor Depth 749.0 m
Sea Floor Depth Source CRREP
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 Approximate - Depth is only approximate
 

Parameters

BODC CODERankUnitsTitle
ACYCAA011DimensionlessSequence number
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
DOXYZZ011Micromoles per litreConcentration of oxygen {O2 CAS 7782-44-7} per unit volume of the water body [dissolved plus reactive particulate phase] by in-situ sensor
OXYSZZ011PercentSaturation of oxygen {O2 CAS 7782-44-7} in the water body [dissolved plus reactive particulate phase]
POPTDR011PercentTransmittance (red light wavelength) per 25cm of the water body by 25cm path length red light transmissometer
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
TOKGPR011Litres per kilogramConversion factor (volume to mass) for the water body by CTD and computation of density (in-situ potential temperature surface pressure) reciprocal from pressure, temperature and salinity

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 quality for D379 CTD data

Data users should note that oxygen saturation values in the range 100-110% were recorded in the near-surface water (approximately top 50-60 metres) for the majority of casts on this cruise.


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

Sea-Bird Dissolved Oxygen Sensor SBE 43 and SBE 43F

The SBE 43 is a dissolved oxygen sensor designed for marine applications. It incorporates a high-performance Clark polarographic membrane with a pump that continuously plumbs water through it, preventing algal growth and the development of anoxic conditions when the sensor is taking measurements.

Two configurations are available: SBE 43 produces a voltage output and can be incorporated with any Sea-Bird CTD that accepts input from a 0-5 volt auxiliary sensor, while the SBE 43F produces a frequency output and can be integrated with an SBE 52-MP (Moored Profiler CTD) or used for OEM applications. The specifications below are common to both.

Specifications

Housing Plastic or titanium
Membrane

0.5 mil- fast response, typical for profile applications

1 mil- slower response, typical for moored applications

Depth rating

600 m (plastic) or 7000 m (titanium)

10500 m titanium housing available on request

Measurement range 120% of surface saturation
Initial accuracy 2% of saturation
Typical stability 0.5% per 1000 h

Further details can be found in the manufacturer's specification sheet.

D379 CTD Instrumentation

CTD unit and auxiliary sensors (stainless steel frame)

The primary CTD system used on cruise D379 was the Sea-Bird 911 plus. This was mounted on a stainless steel rosette frame, equipped with 24 10-litre Niskin bottles. The CTD was fitted with the following scientific sensors:

Sensor Unit Model Serial Number Full Specification Last calibration date (YYYY-MM-DD) Comments
CTD underwater unit SBE 9plus - SBE 9plus - -
Temperature sensor SBE 3P 03P-4383 SBE 03P 2012-03-07 Primary sensor
Temperature sensor SBE 3P 03P-5660 SBE 03P 2012-01-31 Secondary sensor
Conductivity sensor SBE 4 04C-2858 SBE 04C 2012-03-07 Primary sensor
Conductivity sensor SBE 4 04C-3768 SBE 04C 2012-03-07 Secondary sensor
Pressure sensor SBE 9plus digiquartz 121341 - 2012-03-06 -
Dissolved oxygen SBE 43 43-0709 SBE 43 2011-04-29 -
Benthos altimeter PSA-916T 874 - 2010-03-10 -
Turbidity meter WET Labs ECO-BBRTD 167 - 2011-07-06 -
Chlorophyll fluorometer Chelsea Instruments AQUAtracka MKIII 088-2615 AQUAtracka MKIII 2011-03-23 Instrument used for casts 1 to 92
Chlorophyll fluorometer Chelsea Instruments AQUAtracka MKIII 09-7117-001 AQUAtracka MKIII 2011-06-20 Instrument used for casts 93 and above
Transmissometer Chelsea Instruments Alphatracka MKII 161050 Alphatracka MKII 2012-02-29 -

The salinity samples from the CTD were analysed during the cruise using a Guildline Autosal model 8400B. Dissolved oxygen concentrations were determined using a Winkler titration technique.

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus, that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus.

Specifications

Specifications for the SBE 9 plus underwater unit are listed below:

Parameter Range Initial accuracy Resolution at 24 Hz Response time
Temperature -5 to 35°C 0.001°C 0.0002°C 0.065 sec
Conductivity 0 to 7 S m-1 0.0003 S m-1 0.00004 S m-1 0.065 sec (pumped)
Pressure 0 to full scale (1400, 2000, 4200, 6800 or 10500 m) 0.015% of full scale 0.001% of full scale 0.015 sec

Further details can be found in the manufacturer's specification sheet.

Chelsea Technologies Group Aquatracka MKIII fluorometer

The Chelsea Technologies Group Aquatracka MKIII is a logarithmic response fluorometer. Filters are available to enable the instrument to measure chlorophyll, rhodamine, fluorescein and turbidity.

It uses a pulsed (5.5 Hz) xenon light source discharging along two signal paths to eliminate variations in the flashlamp intensity. The reference path measures the intensity of the light source whilst the signal path measures the intensity of the light emitted from the specimen under test. The reference signal and the emitted light signals are then applied to a ratiometric circuit. In this circuit, the ratio of returned signal to reference signal is computed and scaled logarithmically to achieve a wide dynamic range. The logarithmic conversion accuracy is maintained at better than one percent of the reading over the full output range of the instrument.

Two variants of the instrument are available, both manufactured in titanium, capable of operating in depths from shallow water down to 2000 m and 6000 m respectively. The optical characteristics of the instrument in its different detection modes are visible below:

Excitation Chlorophyll a Rhodamine Fluorescein Turbidity
Wavelength (nm) 430 500 485 440*
Bandwidth (nm) 105 70 22 80*
Emission Chlorophyll a Rhodamine Fluorescein Turbidity
Wavelength (nm) 685 590 530 440*
Bandwidth (nm) 30 45 30 80*

* The wavelengths for the turbidity filters are customer selectable but must be in the range 400 to 700 nm. The same wavelength is used in the excitation path and the emission path.

The instrument measures chlorophyll a, rhodamine and fluorescein with a concentration range of 0.01 µg l-1 to 100 µg l-1. The concentration range for turbidity is 0.01 to 100 FTU (other wavelengths are available on request).

The instrument accuracy is ± 0.02 µg l-1 (or ± 3% of the reading, whichever is greater) for chlorophyll a, rhodamine and fluorescein. The accuracy for turbidity, over a 0 - 10 FTU range, is ± 0.02 FTU (or ± 3% of the reading, whichever is greater).

Further details are available from the Aquatracka MKIII specification sheet.

Chelsea Technologies Group ALPHAtracka and ALPHAtracka II transmissometers

The Chelsea Technologies Group ALPHAtracka (the Mark I) and its successor, the ALPHAtracka II (the Mark II), are both accurate (< 0.3 % fullscale) transmissometers that measure the beam attenuation coefficient at 660 nm. Green (565 nm), yellow (590 nm) and blue (470 nm) wavelength variants are available on special order.

The instrument consists of a Transmitter/Reference Assembly and a Detector Assembly aligned and spaced apart by an open support frame. The housing and frame are both manufactured in titanium and are pressure rated to 6000 m depth.

The Transmitter/Reference housing is sealed by an end cap. Inside the housing an LED light source emits a collimated beam through a sealed window. The Detector housing is also sealed by an end cap. A signal photodiode is placed behind a sealed window to receive the collimated beam from the Transmitter.

The primary difference between the ALPHAtracka and ALPHAtracka II is that the Alphatracka II is implemented with surface-mount technology; this has enabled a much smaller diameter pressure housing to be used while retaining exactly the same optical train as in the Mark I. Data from the Mark II version are thus fully compatible with that already obtained with the Mark I. The performance of the Mark II is further enhanced by two electronic developments from Chelsea Technologies Group - firstly, all items are locked in a signal nulling loop of near infinite gain and, secondly, the signal output linearity is inherently defined by digital circuitry only.

Among other advantages noted above, these features ensure that the optical intensity of the Mark II, indicated by the output voltage, is accurately represented by a straight line interpolation between a reading near full-scale under known conditions and a zero reading when blanked off.

For optimum measurements in a wide range of environmental conditions, the Mark I and Mark II are available in 5 cm, 10 cm and 25 cm path length versions. Output is default factory set to 2.5 volts but can be adjusted to 5 volts on request.

Further details about the Mark II instrument are available from the Chelsea Technologies Group ALPHAtrackaII specification sheet.

WETLabs Single-angle Backscattering Meter ECO BB

An optical scattering sensor that measures scattering at 117°. This angle was determined as a minimum convergence point for variations in the volume scattering function induced by suspended materials and water. The measured signal is less determined by the type and size of the materials in the water and is more directly correlated to their concentration.

Several versions are available, with minor differences in their specifications:

  • ECO BB(RT)provides analog or RS-232 serial output with 4000 count range
  • ECO BB(RT)D adds the possibility of being deployed in depths up to 6000 m while keeping the capabilities of ECO BB(RT)
  • ECO BB provides the capabilities of ECO BB(RT) with periodic sampling
  • ECO BBB is similar to ECO BB but with internal batteries for autonomous operation
  • ECO BBS is similar to ECO BB but with an integrated anti-fouling bio-wiper
  • ECO BBSB has the capabilities of ECO BBS but with internal batteries for autonomous operation

Specifications

Wavelength 471, 532, 660 nm
Sensitivity (m-1 sr-1)

1.2 x 10-5 at 470 nm

7.7 x 10-6 at 532 nm

3.8 x 10-6 at 660 nm

Typical range ~0.0024 to 5 m-1
Linearity 99% R2
Sample rate up to 8Hz
Temperature range 0 to 30°C
Depth rating

600 m (standard)

6000 m (deep)

Further details can be found in the manufacturer's specification sheet.

D379 CTD Originator data processing (Stainless Steel)

The following information contains extracts from the D379 cruise report.

Sampling Strategy

A total of 109 CTD casts were performed during the cruise which sailed between Southampton on the south coast of England and Reykjavík in Iceland, incorporating the Extended Ellett Line and Wyville Thomson Ridge area. All casts deployed during the cruise were housed in a stainless steel frame equipped with dual temperature and conductivity sensors. The CTDs were located within and near the bottom of the rosette frame which held 24 10-litre Niskin water sampling bottles.

Data Processing

Following the completion of each CTD cast the data were saved to the deck unit PC and transferred over the network to a Unix data disk. Seabird Data Processing version 7.21f (part of the Seasoft-Win32 suite) was used to perform all CTD processing steps.

Raw data files were converted to engineering units and binary .CNV files using the DATCNV program. Sea-Bird bottle data files (.BTL), with information on pressure and other readings logged at the time of bottle firing, were also generated during the data conversion process. The WILDEDIT program was run to remove any large pressure spikes and then the SeaSoft program ALIGNCTD was run to advance the oxygen measurements by 5 seconds ensuring the calculations of dissolved oxygen concentration are made using measurements from the same parcel of water. CELLTM was run, according to Sea-Bird's recommendations, to remove conductivity cell thermal mass effects from the measured conductivity and FILTER was run on the pressure and depth channels using a low-pass filter value of 0.2 to smooth the rapidly changing data. Finally, twin salinities, twin density and depth were calculated using the DERIVE program and TRANSLATE wrote the data to an ASCII output .CNV file. Despiking of the pressure, oxygen, temperature and salinity data was carried out by visualising the data in MATLAB. If a spike occurs in pressure, temperature or salinity the whole corresponding scan is deleted. If the spike occurs in the other channels, the value is set to NaN and all remaining channels are left unedited. Following despiking of the data in MATLAB the module BINAVERAGE averaged the 24 Hz data into 2db-bins, using the downcast data only.

Calibrations

Throughout the cruise the CTD was sampled for salinity measurements in order to calibrate the conductivity sensors. Salinity was measured using a Guildline Autosal8400 (#60839) in a temperature controlled room. All CTD data used for calibration purposes comes from the bottle files created by the Seabird software. The Autosal was standardised at the start of every run and a standard seawater analysed at the end of every crate. Each crate contained 24 bottles. If more than one crate was analysed during a run then a standard seawater sample was measured between the crates, but the Autosal was not re-standardised.

A total of 282 salinity samples were collected and analysed, including a few duplicate samples. Nine outliers were removed from the dataset. Eight of those appeared to be due to an error in operating the Autosal machine, whilst the remaining outlier came from a sampling or log error. The Autosal and Seabird values were in very good agreement with one another.

BODC, however, were not provided with the specific salinity calibration applied to the data.

Calibrated oxygen values in the final data files have been converted from mg/l to umol/kg using the following formula:

[umol/kg] = (([mg/l] / 1.42903) * 44660) / (sigma_theta + 1000)

References

Griffiths C. R. et al., (2012). RRS Discovery Cruise D379, 31 Jul 2012 - 17 Aug 2012. Southampton to Reykjavík - the Extended Ellett Line. Scottish Association for Marine Science, 184pp. (Scottish Marine Institute, Oban, 14-23)

Available - Cruise D379 Internal Report

Dumont, E., Sherwin, T. (2008). SAMS CTD data processing protocol, Issue 1. Scottish Association for Marine Science. (Scottish Marine Institute, Oban. Internal Report No 257).

D379 CTD Processing undertaken by BODC

Data arrived at BODC in a total of 109 ASCII files, WHP (WOCE Hydrographic Program) format. These files contain 2db-bin averaged data including temperature, salinity and dissolved oxygen channels processed to WOCE standards alongside concurrent fluorometer and transmissometer data. BODC were only supplied with one set of salinity and temperature channels on submission of the data.

24 Hz ASCII versions of these data are also available from BODC upon request. These files are held in their original format, but these remain uncalibrated.

The lodged WHP standard casts were reformatted to BODC's internal QXF format. The following table shows the mapping of variables within the ASCII files to appropriate BODC parameter codes:

Originator' Variable Units Description BODC Parameter Code Units Comments
Pressure dbar Pressure exerted by the water column PRESPR01 dbar -
Temperature °C Temperature of the water column by CTD TEMPST01 °C -
Salinity - Practical salinity of the water column PSALST01 - Calibrated by data originator using discrete water samples from CTD bottles
Dissolved Oxygen Concentration µmol/kg Concentration of oxygen per unit volume of the water column DOXYZZ01 µmol/l

Calibrated by data originator using discrete water samples from CTD bottles.

A unit conversion was applied as part of the BODC transfer process for this parameter.

Transmittance % Transmittance per 25cm of the water column by transmissometer POPTDR01 % -
Fluorescence mg/m3 Concentration of chlorophyll-a per unit volume of the water column CPHLPR01 mg/m3 -

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, and missing data marked by both setting the data to an appropriate value and setting the quality control flag.

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

  • Irregularities such as unfeasible values
  • Inconsistencies between related information, for example:
    • Times for instrument deployment and for start/end of data series
    • Length of record and the number of data cycles/cycle interval
    • Parameters expected and the parameters actually present in the data cycles
  • Originator's comments on meter/mooring performance and data quality

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

  • Spurious data at the start or end of the record.
  • Obvious spikes occurring in periods free from meteorological disturbance.
  • A sequence of constant values in consecutive data cycles.

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

  • Maximum and minimum values of parameters (spikes excluded).
  • The occurrence of meteorological events.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.


Project Information


No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Cruise Name D379
Departure Date 2012-07-30
Arrival Date 2012-08-17
Principal Scientist(s)Colin R Griffiths (Scottish Association for Marine Science)
Ship RRS Discovery

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