Metadata Report for BODC Series Reference Number 2000911
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
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
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.
Instrument Description for JR15007 CTD
CTD Unit and Auxiliary Sensors
The CTD unit comprised a Sea-Bird Electronics (SBE) 9 plus underwater unit. One stainless steel CTD frame was prepared with 24, 20L Niskin Bottles, as well as the series of instruments listed in table below. All the instruments were mounted at the bottom and inside the CTD frame with the exception of the SBE 35 and PAR sensors, which were mounted on the perimeter of the CTD approximately 1 metre above the other instruments.
Sensor unit | Model | Serial number | Full specification | Calibration Date |
---|---|---|---|---|
Temperature sensor 1 | SBE 3P | 5766 | SBE 03P | 18 March 2015 |
Temperature sensor 1 | SBE 3P | 4302 | SBE 03P | 12 June 2015 |
Conductivity sensor 1 | SBE 4C | 2289 | SBE 04C | 08 July 2015 |
Conductivity sensor 1 | SBE 4C | 2875 | SBE 04C | 17 June 2015 |
Temperature sensor 2 | SBE 3P | 2705 | SBE 03P | 10 Jun 2015 |
Conductivity sensor 2 | SBE 4C | 2222 | SBE 04C | 09 July 2015 |
Pressure sensor SBE 9plus | SBE 9 plus | 0707 | SBE 9 plus | 22 June 2015 |
Temperature reference sensor | SBE 35 | 0024 | SBE 35 | |
Transmissometer | WetLabs C-Star | CST-846DR | WetLabs C-Star | 17 June 2015 |
Fluorometer | AQUATRACKA MKIII | 088-249 | Chelsea MKII Aquatracka | 11 May 2015 |
PAR Irradiance sensor | Biospherical QCD-905L4S | 7274 | Biospherical QCD PAR sensor | 24 April 2013 |
Dissolved oxygen sensor | SBE 43 | 0676 | SBE 43 | 02 June 2015 |
The primary temperature and conductivity sensors with serial numbers 5766 and 2289 respectively were used in casts 1-48 and were changed on 19/06/2016 prior to CTD 49 to temperature sensor 4302 and conductivity sensor 2975. This change was due to series of short periods when the primary temperature and conductivity records became offset relative to the secondary sensors. Unfortunately this change did not resolve the problem and the source of the fault has not been identified. It is recommended that only the secondary temperature and conductivity records are used.
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.
SeaBird SBE35 Deep Ocean Standards Thermometer
The SBE 35 is a high precision thermometer that can be used in fixed point cells or at depths up to 6800 m. It is not affected by shock and vibration, allowing it to be used in calibration laboratories and for thermodynamic measurement of hydro turbine efficiency.
The SBE35 can be used with the SBE32 Carousel Water Sampler and with a real-time or autonomous CTD system. In this case, an SBE35 temperature measurement is collected each time a bottle is fired and the value is stored in EEPROM (Electrically Erasable Programmable Read-Only Memory), eliminating the need for reversing thermometers while providing a high accuracy temperature reading.
The SBE35 is standardized in water triple point (0.0100 °C) and gallium melting point (29.7646 °C) cells, following the methodology applied to the Standard-Grade Platinum Resistance Thermometer (SPRT). However, it does not need a resistance bridge, making it more cost-efficient than an SPRT.
Temperature is determined by applying an AC excitation to reference resistances and an ultrastable aged thermistor. Each of the resulting outputs is digitized by a 20-bit A/D converter. The AC excitation and ratiometric comparison uses a common processing channel, which removes measurement errors due to parasitic thermocouples, offset voltages, leakage currents and gain errors.
Specifications
Measurement range | -5 to 35°C |
Accuracy | 0.001°C |
Typical stability | 0.001°C year-1 |
Resolution | 0.000025°C |
Data storage | up to 179 samples |
Baud rate | 300 |
Further details can be found in the manufacturer's specification sheet and manual.
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.
Biospherical Instruments Log Quantum Cosine Irradiance Sensor QCD-905L
The QCD-905L is a submersible radiometer designed to measure irradiance over Photosynthetically Active Radiation (PAR) wavelengths (400-700 nm). It features a cosine directional response when fully immersed in water.
The sensor is a blue-enhanced high stability silicon photovoltaic detector with dielectric and absorbing glass filter assembly, and produces a logarithmic output. Normal output range is -1 to 6 volts with 1 volt per decade. Typically, the instrument outputs 5 volts for full sunlight and has a minimum output of 0.001% full sunlight, where typical noon solar irradiance is 1.5 to 2 x 1017 quanta cm-2 s-1. The instrument can be calibrated with constants for µE cm-2 s-1 or quanta cm-2 s-1.
The QCD-905L can be coupled to a fixed range data acquisition system like a CTD (Conductivity-Temperature-Depth) profiler or current meter. It has an aluminium and PET housing, and a depth rating of 7000 m.
Specifications
Wavelength | 400 to 700 nm |
Output range | -1 to 6 V, with 1 V decade-1 |
Operating temperature | -2 to 35°C |
Depth range | 0 - 7000 m |
Further details can be found in the manufacturer's manual.
WETLabs C-Star transmissometer
This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.
Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.
This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.
Specifications
Pathlength | 10 or 25 cm |
Wavelength | 370, 470, 530 or 660 nm |
Bandwidth | ~ 20 nm for wavelengths of 470, 530 and 660 nm ~ 10 to 12 nm for a wavelength of 370 nm |
Temperature error | 0.02 % full scale °C-1 |
Temperature range | 0 to 30°C |
Rated depth | 600 m (plastic housing) 6000 m (aluminum housing) |
Further details are available in the manufacturer's specification sheet or user guide.
BODC Processing of CTD casts from cruise JR15007
The CTD data were supplied to BODC as 67 MStar files and converted to the BODC internal format (netCDF).
During transfer the originator's variables were mapped to unique BODC parameter codes. The following table shows the parameter mapping.
Originator's variable | Units | Description | BODC Code | Units | Comments |
---|---|---|---|---|---|
press | decibars | Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level. | PRESPR01 | decibars | - |
temp | degC | Temperature of the water body by CTD | - | - | Not retained |
temp1 | degC | Temperature of the water body by CTD | - | - | Not retained |
temp2 | degC | Temperature of the water body by CTD | TEMPST01 | degC | Transferred and considered primary data channel on advice from originator |
cond | mS/cm | Electrical conductivity of the water body by in-situ conductivity cell and calibration against independent measurements | - | - | Not retained |
cond1 | mS/cm | Electrical conductivity of the water body by in-situ conductivity cell and calibration against independent measurements | - | - | Not retained |
cond2 | mS/cm | Electrical conductivity of the water body by in-situ conductivity cell and calibration against independent measurements | CNDCST01 | S/m | Converted (/10) - Transferred and considered primary data channel on advice from originator |
altimeter | m | Height above bed in the water body | AHSFZZ01 | m | - |
oxygen | µmol/kg | Concentration of oxygen {O2} per unit volume of the water body [dissolved phase] by Sea-Bird SBE 43 sensor and calibration against sample data | DOXYZZ01 | µmol/l | Conversion by BODC to µmol l-1 using TOKGPR01 |
fluor | µg/l | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate phase] by in-situ chlorophyll fluorometer and manufacturer's calibration applied | CPHLPR01 | mg/m3 | ug/l=mg/m3 |
transmittance | % | Transmittance (red light wavelength) per 25cm of the water body by 25cm path length red light transmissometer | POPTDR01 | % | - |
par | number | Downwelling vector irradiance as photons (PAR wavelengths) in the water body by cosine-collector radiometer | IRRDUV01 | µE/m s | - |
psal | pss-78 | Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm | PSALST01 | pss-78 | Calculated from calibrated conductivity measurements, by the originator |
psal1 | pss-78 | Practical salinity of the water body by CTD | - | - | Not retained |
psal2 | pss-78 | Practical salinity of the water body by CTD | - | - | Not retained |
depth | m | Depth below surface (sampling event start) of the water body by profiling pressure sensor and conversion to depth using unspecified algorithm. | DEPHPR01 | m | - |
- | - | Saturation of oxygen | OXYSZZ01 | % | Derived by BODC using DOXYSC01, TEMPST01 and PSALST01 |
- | - | Potential temperature of the water body by computation using UNESCO 1983 algorithm | POTMCV01 | degC | Derived by BODC using TEMPST01, PSALST01 and PRESPR01. |
- | - | Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm | SIGTPR01 | kg/m3 | Derived by BODC using POTMCV01, PSALST01 and PRESPR01 |
- | - | Conversion 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 | TOKGPR01 | l/kg1 | Derived by BODC using SIGTPR01 |
Originator Data Processing of CTD casts from cruise JR15007
Sampling Strategy
A total of 67 CTD profiles were collected on the cruise JR15-007 distributed across four lines as part of the RidgeMix programme. The cruise departed the Port of Spain, Trinidad and Tobago on 25 May 2016 and returned to Immingham, United Kingdom on 10 July 2016. One stainless steel CTD frame was prepared with 24 20L Niskin Bottles, together with series of other instruments (temperature, conductivity, pressure, transmission, fluorescence, PAR and dissolved oxygen sensors). All the instruments were mounted at the bottom and inside the CTD frame with the exception of the SBE 35 and PAR sensors, which were mounted on the perimeter of the CTD approximately 1 metre above the other instruments.
Data Processing
The CTD processing was performed using the MEXEC software developed by Brian King (NOC). Subsequently, the following three processes were run in SBE Data Processing, version 7.22.3 software:
- Data conversion - converted raw data from engineering units to binary .cnv files.
- AlignCTD - applied a time alignment offset to the oxygen data relative to pressure to compensate for hysteresis effects.
- CellTM - corrected conductivity data for cell thermal mass effects (alpha = 0.03. tau = 7.0000 on both primary and secondary).
Any settings used during these steps were provided by the manufacturer.
Data were then processed using a suite of Matlab programs developed by the Ocean Circulation and Processing group at the National Oceanography Centre (NOC).
Calibrations
Temperature
The CTD temperature sensor was calibrated by comparison with SBE35 values obtained at the time of bottle firings. Initial comparisons showed that the two CTD temperatures were in good agreement with little skew, however, the SBE35 was recording temperatures O(0.1°C) higher near the surface. These discrepancies were co-located with strong vertical temperature gradients, O(0.1°C/m). In order to minimise the effects of this gradient, the temperature calibration was performed only using values below 2000dB.
This temperature choice lead to a calibration not varying in depth of:
- Primary 1: +0.00045
- Primary 2: +0.00205
- Secondary 1: +0.00114
Salinity
The water samples were collected by the Niskin bottle from a range between a few tens centimetres above the sensor to over a metre. All three conductivity sensors showed a large amount of scatter data near the surface. The measurements from the bottle samples could be bias relative to the CTD due to large vertical gradients. In the upper 1500m the vertical gradient is typically O(0.01 °C m-1) whilst the differences between the bottle and CTD salinity is typically in the range O(0.001 to 0.01). As a result the calibration was performed using data from deeper than 1500dB and assumeed that the pressure dependant correction is linear throughout the water column.
This has been applied by least-squares fitting an equation of the form:
o = m * P + cwhere o is the offset to be applied to the salinity, P is the pressure and m and c are constants to be fitted. The constrants are as follow:
Sensor | m | c |
---|---|---|
First Primary | -2.5091e-7 | 1.9003e-3 |
Second Primary | -3.5512e-8 | 3.6565e-3 |
Secondary | -4.9835e-7 | 2.6667e-3 |
Oxygen
Dissolved oxygen calibrations were applied in post-cruise processing by comparing Winkler titration values from Niskin water samples and CTD values at the time of bottle firing.
Further information on the CTD processing can be found in the cruise report.
Project Information
A nutrient and carbon pump over mid-ocean ridges (RidgeMix)
RidgeMix is a five year (August 2014 to February 2019) research programme which received funding from the Natural Environment Research Council (NERC). The aim of the programme was to address the problem of how deep nutrients are transported into the surface waters in mid-latitudes, by testing a new view: tides passing over the mid-Atlantic ridge generate enhanced turbulence and mixing, which in turn provides a nutrient supply to the upper thermocline waters. These nutrients are then transported horizontally along density surfaces over the western side of the basin, probably being swept along the Gulf Stream and eventually passing into the winter mixed surface layer. When this surface layer shallows and warms in spring, the nutrients are then available to the phytoplankton.
Fieldwork involved collecting measurements of the turbulence and nutrient concentrations over and adjacent to the Mid-Atlantic Ridge, using a novel long-term moored array of instruments along the ridge, deployed over a five-week research cruise. Sampling was done sufficiently quickly to resolve tidal changes in currents and mixing over the ridge. A second component of the fieldwork will use computer models of circulation in the Atlantic to explore the wider implications of the fieldwork observations, to determine whether or not mixing over the mid-Atlantic ridge really does provide enough nutrients to explain the phytoplankton production in the mid-latitude North Atlantic.
RidgeMix was a collaborative project involving five organisations, of which three were UK based and two were US based. The project was led by the Professor Jonathan Sharples, University of Liverpool, Earth, Ocean and Ecological Sciences. Collaborators were:
Data Activity or Cruise Information
Cruise
Cruise Name | JR15007 |
Departure Date | 2016-05-25 |
Arrival Date | 2016-07-10 |
Principal Scientist(s) | Jonathan Sharples (National Oceanography Centre, Liverpool) |
Ship | RRS James Clark Ross |
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 |
B | nominal value |
Q | value below limit of quantification |