Metadata Report for BODC Series Reference Number 1133827

• 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

Problem Reports

No Problem Report Found in the Database

RSS Discovery Cruise D366 CTD Data Quality Document

There are some small entrainment features visible in some casts where there are sharp gradients within the profiles for salinity, temperature (and hence density and potential temperature), oxygen concentration and saturation.

Downwelling PAR irradiance

PAR sensors were not present on three casts: CTD_D366030_AVG, CTD_D366060_AVG and CTD_D366061_AVG, as these casts were to deeper pressures than the sensors are designed for. It is unclear whether the surface variability in the PAR channels is due to changing cloud cover or more likely, a shading effect from the ship during initial deployment.

Chlorophyll

The profile trends appear reasonable, however the absolute values returned from the manufacturer's calibration may need further correction as several series contain values below the minimum limit of the parameter range (0 to 999 mg m^-3). The deep spikes on some of the profiles such as cast CTD_D366072_AVG have been flagged as suspect.

Attenuance

The profile trends appear reasonable, however the absolute values returned from the manufacturer's calibration may need further correction as some series have negative data values which are out of the range of the parameter range (0 to 400 metre^-1). There are deep spikes on a couple of profiles such as cast CTD_D366010_AVG, that have been flagged suspect.

Transmittance

The profile trends appear reasonable, however the absolute values returned from the manufacturer's calibration may need further correction as some series have data values above 100% and therefore outside the range of the parameter. There are also some deep spikes on some of the profiles such as CTD_D366010_AVG, that have been marked as suspect.

Turbidity

The profile trends appear reasonable, however the absolute values returned from the manufacturer's calibration may need further correction as many of the series have negative data values and are therefore out the of range of the parameter (0 to 9 m^-1nm^-1sr^-1).

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

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

Instrument Description D366

Standard Rosette CTD Unit and Auxiliary Sensors;

A 24-way stainless steel frame (s/n SBE CTD4 (1415)), with a Sea-Bird 9/11 plus underwater unit (SN 09P-46253-0869) with vane-mounted secondary temperature and conductivity sensors was used throughout the cruise. All other instruments were attached to a Sea-Bird 32 Carousel 24 Position Pylon (s/n 32-34173-0493) with Ocean Test Equipment 20L ES-120B water samples. The Stainless Steel CTD system used an 11 plus deck unit (s/n 11P-34173-0676).

The CTD unit included the following sensors

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:

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:

* 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.

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

Further details can be found in the manufacturer's 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

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

Paroscientific Absolute Pressure Transducers Series 3000 and 4000

Paroscientific Series 3000 and 4000 pressure transducers use a Digiquartz pressure sensor to provide high accuracy and precision data. The sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

The 3000 series of transducers includes one model, the 31K-101, whereas the 4000 series includes several models, listed in the table below. All transducers exhibit repeatability of better than ±0.01% full pressure scale, hysteresis of better than ±0.02% full scale and acceleration sensitivity of ±0.008% full scale /g (three axis average). Pressure resolution is better than 0.0001% and accuracy is typically 0.01% over a broad range of temperatures.

Differences between the models lie in their pressure and operating temperature ranges, as detailed below:

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

UK Ocean Acidification (UKOA) cruise D366 CTD processing

Sampling strategy

A total of 75 successful CTD casts were made during the cruise using a stainless steel frame. Rosette bottles were fired throughout the water column on the upcast of most profiles. Data were measured by a PC running Seasave V 7.20g, Sea-Bird's data acquisition software.

Originator's processing

The initial Sea-Bird processing was completed at NOCL. The latest available version of the SeaBird Processing software (SBE Data Processing V7.22.0) was used to process the raw binary data files (DAT files) based on information held in the sensor configuration files (CON files), and bottle firing files (BL). During 21 of the casts, the required soak was either not performed or only partially undertaken.

Sea-Bird processing

The raw data files have the appendices: .hex, .HDR, .bl and .CON. The .CON files for each cast contain the calibration coefficients for the instrument. The .HDR files contain the information in the header of each cast file. The .hex files are the data files for each cast and are in hex format. The .bl files contain CTD scans that were collected while the water bottle was being closed.

Data were processed following established BODC procedures and the following SeaBird routines were carried out: DATCNV, BOTTLESUM, WILDEDIT, FILTER, ALIGNCTD, CELLTM, LOOPEDIT, DERIVE and BINAVERAGE. The default settings were used in all of the routines except where specified below.

• ALIGNCTD was run using an oxygen advance of 2.0 s.
• LOOPEDIT was run with a minimum depth of 2.5 m and a maximum depth of 16 m. In addition to LOOPEDIT, casts that were incorrectly 'soaked' had surface contaminated data removed by hand.
• BINAVERAGE was used with a bin size of 0.5 m.

Field calibrations

Calibration of the oxygen sensor

Oxygen data was calibrated against discrete sample data processed by NOCS. A persistent offset was found between the CTD profile data and the calibration sample data, equivalent to a 4.15% positive error. CTD oxygen concentration data were therefore increased by 4.15% after comparison with the discrete sample Winkler titration measurements.

Salinity calibration

The salinity channel displayed some inaccuracies when compared with discrete sample data, however no adjustments were applied to the CTD salinity data. No corrections were deemed possible due to the low level of error in the calibration and uncertainties in local conditions.

BODC Reformatting

The data were delivered to BODC in separate files for the down and up casts with the downcast providing the best quality data due to collection in a continuous profile.

The data were converted from Sea-Bird ASCII format into BODC internal format using BODC transfer function 357. The following table shows how the variables within the Sea-Bird files were mapped to appropriate BODC parameter codes. Oxygen saturation, sigma-theta and potential temperature channels were derived during the transfer.

References

Benson, B.B and Krause, D. 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnology and Oceanography, 29(3), p. 620-632.

Fofonoff, NP and Millard, RC. 1983. Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science, 44, p.53.

UNESCO. 1981. Background papers and supporting data on the International Equation of State of Seawater 1980. UNESCO Technical Papers in Marine Science No. 38, p.192

Screening

Reformatted CTD data were visualized using the in-house graphical editor EDSERPLO. No data values were edited or deleted. All spurious and null data were flagged with BODC quality control flags.

PAR

Comparison between the voltage values and PAR values provided in the files with the calibration certificates showed that the data were out by a factor of 10 for the PAR values derived from voltages. This is a recurring problem with the way coefficients are entered into the Sea-Bird .CON files onboard the ship. A correction factor of x10 was applied to the DWIRPP01 and UWIRPP01 channels.

PAR sensors were not present on three casts (cast 30, 60 and 61) as these were deep casts to greater pressure than the sensors are rated to go. Cast 61 appears to have followed straight after 60 and there may not have been time during the turnaround to re-attach the PAR sensors.

Banking

Once quality control screening was complete, the CTD downcasts were banked. The primary salinity, temperature, density and potential temperature channels were retained as the best quality data channels from the two sensors.

Project Information

UKOARP Theme B: Ocean acidification impacts on sea surface biology, biogeochemistry and climate

The overall aim of this theme is to obtain a quantitative understanding of the impact of ocean acidification (OA) on the surface ocean biology and ecosystem and on the role of the surface ocean within the overall Earth System.

The aims of the theme are:

• To ascertain the impact of OA on planktonic organisms (in terms of physiological impacts, morphology, population abundances and community composition).
• To quantify the impacts of OA on biogeochemical processes affecting the ocean carbon cycle (both directly and indirectly, such as via availability of bio-limiting nutrients).
• To quantify the impacts of OA on the air-sea flux of climate active gases (DMS and N₂O in particular).

The main consortium activities will consist of in-situ measurements on three dedicated cruises, as well as on-deck bioassay experiments probing the response of the in-situ community to elevated CO₂. Most of the planned work will be carried out on the three cruises to locations with strong gradients in seawater carbon chemistry and pH; the Arctic Ocean, around the British Isles and the Southern Ocean.

Weblink: http://www.oceanacidification.org.uk/research_programme/surface_ocean.aspx

Data Activity or Cruise Information

Cruise

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:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: