Metadata Report for BODC Series Reference Number 896710

• 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

A number of data values in the transmittance channel exceed 100%. It is believed such values occurred due to lenses on the transmissometer being fouled by an oil film. All values where transmittance exceeds 100% have been automatically flagged by the screening software used.

It should be noted that on 07/10/2005 the 10cm transmissometer attached to the stainless steel CTD frame was cleaned with the following air and blank readings being taken;

• V_air = 4.111 V

• V_blank = 0.015 V

This air reading was 0.34 V lower than the previous calibration and bench test and this was believed to be as a result of the fouling of the lenses.

Subsequent cleaning on 13/10/2005 gave the following readings;

• V_air = 4.433 V

• V_blank = 0.018 V

These later readings were nearly identical to the previous calibration and bench test results.

Despite data appearing to be more reasonable from cast 48 onwards, however, caution should be exercised when using these data considering the problems experienced earlier in the cruise.

Data Quality Report

Series metadata suggest that the CTD cast depth is greater than the seafloor depth. This is the result of uncorrected seafloor depths, from the ship's precision echosounder, appearing in the originator's data header files.

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.

CD176 Stainless Steel CTD Instrumentation

CTD unit and auxiliary sensors

The CTD system used on cruise CD176 was the Sea-Bird 911 plus. The Sea-Bird sensors were located within and near the bottom of the rosette frame, which housed 24 10-litre Niskin bottles. The CTD was fitted with the following scientific sensors:

Independent salinity samples from the CTD were analysed during the cruise in a constant temperature laboratory using the Guildline Autosal model 8400B (s/n 68426). 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:

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

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

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

Chelsea Technologies 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.

CD176 Stainless Steel CTD Originator Processing

Sampling Strategy

A total of 66 CTD casts were performed during the cruise which sailed between Birkenhead and Falmouth via Rockall, Iceland and Oban incorporating the Extended Ellett Line and Wyville Thomson Ridge. 64 of the 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. On 16th October 2005 the Seabird CTD software on both master and slave deckunit PCs was upgraded to v5.35 following problems with crashing and this software was used to perform all subsequent processing steps.

Raw data files were converted to engineering units and ASCII (.CNV) files using the DATCNV program. SeaBird 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. CELLTM was run, according to SeaBird's recommendations, to remove conductivity cell thermal mass effects from the measured conductivity and FILTER was run on the pressure channel. Salinity and density were calculated using the DERIVE program and TRANSLATE wrote the data to an output .CNV file. Following despiking of the data in MATLAB the program LOOPEDIT was run with a minimum CTD velocity of 0.25 m/s. Finally the data were binned to 2 db intervals using the BINAVERAGE program thus being formatted according to the WHP (WOCE Hydrographic Programme) standards.

For CD176 the raw .dat and .hdr Sea-Bird files for CTD cast 34 were never supplied to the data originator or to BODC from the ship and should be considered as lost.

Field Calibrations

The salinity and oxygen data from the CTD were calibrated using independent values obtained from the CTD water bottles.

The final calibration of the CTD salinity sensor on the stainless steel frame is given here;

• S_A = 0.9803S_M + 0.7044

With a correlation coefficient of R² = 0.9955

Where S_A is the actual salinity and S_M is the measured salinity (calculated from CTD conductivity)

The final calibration of the CTD oxygen sensor on the stainless steel frame is given here;

• O_A = 1.0378O_M + 3.8349

With a correlation coefficient of R² = 0.9718

Where O_A is the actual oxygen concentration and O_M is the measured oxygen concentration

References

Sherwin, T. A. et al, (2005). 'Cruise CD176 Birkenhead to Falmouth via Rockall, Iceland and Oban', Internal Report No 248, Scottish Association for Marine Science.

Available - Cruise CD176 Internal Report

CD176 Stainless Steel CTD Processing undertaken by BODC

The data arrived at BODC in a total of 65 ASCII, WHP (WOCE Hydrographic Program) standard files with 63 of these files representing CTD casts from the stainless steel frame deployed during the cruise. These files contain 2 db-bin averaged data including temperature, salinity and dissolved oxygen channels processed to WOCE standards alongside concurrent fluorometer and transmissometer data.

24 Hz ASCII versions of these data are also available from BODC, upon request. These files are held in their original format and, although containing additional parameters, have undergone less quality control by the originator and remain uncalibrated

The lodged WHP standard cast 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:

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.

Project Information

Northern Seas Programme

The Northern Seas describes an area extending from the Irish and northern North Sea across the Norwegian Sea up to the marginal Arctic pack-ice zone, including territorial waters of the UK, Norway, Iceland, Denmark and Russia. These waters are an important marine environment playing a significant part in regulating world climate due to the area's role in thermocline circulation in addition to acting as a sink for man-made pollutants carried north by ocean currents. These environments are experiencing increasing pressures from both natural and human impacts and consequently the Northern Seas Programme was developed to help advance the understanding of how marine systems in Northern Seas respond to environmental and anthropogenic change.

Scientific Objectives

The central aim of the programme was to 'improve understanding of how the sensitivity of marine ecosystems to environmental perturbation, both natural and anthropogenic, varies along a latitudinal gradient'.

This aim was addressed through the following integrated themes:

Theme A: Understanding fjordic systems: insights for coastal and oceanic processes

Theme B: Ocean Margins: the interface between the coastal zone and oceanic realm

Theme C: Measuring and modelling change: sea sensors and bioinformatics

The Northern Seas Programme was active between 2001 and 2007. The fieldwork programme to address these objectives was conducted by staff from the Scottish Association for Marine Science (SAMS).

Northern Seas Programme Theme B

Theme B: Ocean Margins: the interface between the coastal zone and oceanic realm

The interface between coastal and oceanic realms at the ocean margins has been addressed through the following sub-themes:

Sub Theme B1: Carbon dynamics at ocean margins

• What are the roles of physical submarine features (seamounts, banks and depressions) in driving carbon flow through the benthic biosphere at the northern European continental margin?
• To what extent do benthic faunal composition and size structure determine processes of carbon dynamics and biogeochemical provinces at the benthic boundary?

Sub Theme B2: The Ellett Line time series

• The Ellett Line aims to regularly monitor the transport of water, heat and salt between Mull and Rockall.

Sub Theme B3: The ecology of deep-water fisheries of the Northern Rockall Trough

• The effects of fisheries on deep-water ecosystems will be addressed through the construction of food-web models.

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Wyville Thomson Ridge

The Wyville Thomson Ridge marks the boundary between the Rockall Trough and the Faroe-Shetland Channel. The Ridge is an important area for the study of deep ocean circulation and has been the focus of many studies (particularly CTD surveys), by various institutions, since 1975.

The Wyville Thomson Ridge is also a location of focused mooring activities led by the Scottish Association for Marine Science (SAMS). See Wyville Thomson Ridge Moored ADCP for specific details.

Measurements made along and around the Wyville Thomson Ridge lie within a box bounded by co-ordinates 59° 40' N, 9° 54' W at the southwest corner and 60° 50' N, 5° 00' W at the northeast corner.

Related Fixed Station activities are detailed in Appendix 1

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:

Appendix 1: Wyville Thomson Ridge

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

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