Metadata Report for BODC Series Reference Number 789214

• 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

Data Access Policy

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Narrative Documents

Sea Bird Electronics SBE13 Dissolved Oxygen Sensor

The SBE 13 was designed as an auxiliary sensor for Sea Bird SBE 9plus, but can fitted in custom instrumentation applications. When used with the SBE 9 Underwater Unit, a flow-through plenum improves the data quality, as the pumping water over the sensor membrane reduces the errors caused by oxygen depletion during the periods of slow or intermittent flushing and also reduces exposure to biofouling.

The output voltage is proportional to membrane current (oxygen current) and to the sensor element's membrane temperature (oxygen temperature), which is used for internal temperature compensation.

Two versions of the SBE 13 are available: the SBE 13Y uses a YSI polarographic element with replaceable membranes to provide in situ measurements up to 2000 m depth and the SBE 13B uses a Beckman polarographic element to provide in situ measurements up to 10500 m depth, depending on the sensor casing. This sensor includes a replaceable sealed electrolyte membrane cartridge.

The SBE 13 instrument has been out of production since 2001 and has been superseded by the SBE 43.

Specifications

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

SeaBird SBE18 pH sensor

This model uses a pressure-balanced glass-electrode/Ag/AgCl reference pH probe to provide in situ measurements up to 1200 m depth. It is a modular sensor designed to be used in a profiling mode only.

Specifications

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

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.

Biospherical Instruments Quantum Scalar Reference Sensor QSR-240

The QSR-240 is a hemispherical reference sensor designed to measure surface radiation. It has a scalar directional response and includes a field-of-view cutoff plate that transforms its response to a hemispherical one. An aluminium-encased optical light pipe funnels flux, from the collector to a silicon photodetector, that has a flat response over the Photosynthetically Active Radiation (PAR) spectrum (400 - 700 nm).

This instrument works as a transducer, providing and analog voltage output that is directly proportional to the incident irradiance upon the collectors' sensing plate. It is designed for surface measurements of total incident PAR from the sun and sky.

Specifications

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

Biospherical Instruments Quantum Scalar Irradiance Profiling Sensor QSP-200

The QSP-200 is a submersible spherical radiance collector designed to ensure a uniform directional response over 3.7-pi steradians. The aluminium-encased optical light pipe funnels flux from the collector to a silicon photodetector that has a flat quantum response over the Photosynthetically Active Radiation (PAR) spectrum (400 - 700 nm).

The sensor can be coupled with other instruments and accessories, allowing for automatic data acquisition and digital display. The standard version has a depth rating of 1000 m and the QSP-200D includes the option of a 200 m depth transducer. The logarithmic output version (QSP-200L4S) is available for integration with CTD or STD and uses a shielded underwater cable. The QSP-200 has been superseded by the QSP-2300.

Specifications

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.

MV Mitra 0499 CTD Data Documentation

Data Originator

Dr. Jo Suijlen, Rijkswaterstaat/Rijksinstituut voor Kurst en Zee (RWS/RIKZ), Den Haag, Netherlands.

Cruise Principal Scientist

Martyn Harvey, Dunstaffnage Marine Laboratory (DML), Oban, UK.

Content of data series

Instrumentation and data processing by originator

CTD unit and auxiliary sensors

Sea-Bird Electronics (SBE) 911 Plus system fitted with the following sensors:

The manufacturer's specifications are listed in the table below. All sensors were calibrated and checked once a year by the manufacturer.

The precisions guaranteed by the North Sea Directorate were as follows:

For the oxygen probe, dissolved oxygen concentrations measured by the probe were checked against oxygen concentration measured on surface water samples by the Winkler titration during the cruise. Calibration checks were performed on 19/04, 21/04, 26/04 and 29/04. The precision of the oxygen probe was acceptable within ± 6 % of the concentration measured by Winkler titration. On 21/04 a decrease in precision was noted and the oxygen sensor was replaced after cast 037.

Data were logged on a PC running Seabird data acquisition software version Seasave Win32 v.1.10 and manufacturer's calibration coefficients were applied to the raw data.

CTD data were supplied to BODC as downcasts only, binned to 0.1 m.

Sampling device

• Rosette sampling system.
• No reversible thermometer was used.

BODC post-cruise processing and screening

Reformatting

The data were converted into BODC internal format (PXF) to allow use of in-house software tools notably the workstation graphics editor SERPLO. In addition to reformatting, the transfer program applied the following modifications to the data:

• dissolved oxygen was converted from mg l^-1 to µmol l^-1 by multiplying the values by 31.25 (=1000/31.998).
• transmissometer readings for the two transmissometers were converted from % transmission to attenuance using the algorithm:

where PL is the transmissometer pathlength in metres (0.10 and 0.25 m).

Screening of data and metadata

• reformatted CTD data were transferred onto a high-speed graphics workstation. Downcast channels were screened graphically using custom in-house graphics editors. If present, spikes and suspicious data were manually flagged. No data values were edited or deleted; flagging was achieved by modification of the associated quality control flag to 'M' for suspicious values and 'N' for null.
• metadata information (station time, position) available from the cruise report was checked against the information present in the header of the CTD files. Because no navigation underway file was available for this cruise particular attention was paid to checking that both station date/time and station position were logged correctly both in the cruise report and in the originator's files header. No suspicious discrepancy was found in the date and times recorded. For station location a few discrepancies were found (see table below). Based on the comparison between successive CTD stations, the discrepancies were attributed to typing errors in the cruise report and station position coordinates were banked according to the entries logged in the CTD file header. For the other stations discrepancies were small with differences not greater than 0.5 minutes for the latitude and 0.9 minutes for the longitude.

Banking

Once screened on the workstation, the CTD downcasts were loaded into a database under the ORACLE Relational Database Management System.

Calibration

• Fluorescence: CTD chlorophyll fluorescence output (µg Chl l^-1) was calibrated against extracted chlorophyll concentrations measured on samples collected during the cruise (data originator: K. Jones, DML, UK). The calibration equation was determined by linear regression between extracted chlorophyll concentration (range: 1.95 to 20.60 µg l^-1) and CTD chlorophyll fluorescence values measured on the upcast. The equation is (including standard errors on slope and intercept):

• Total suspended particulate matter concentration (TSED) was estimated at the University of Wales, Bangor, by linear regression of the concentration of total suspended particulate matter as measured on water samples by gravimetry and attenuance (ATTN) as measured by the CTD medium pathlength transmissometer at the time of sample collection. The resulting calibration equation is:

• Data from the other channels had already been calibrated by the data originator and no further calibration/correction was applied.

Comments on data quality

• Attenuance: the two transmissometers used on the CTD unit give attenuance values significantly different from each other. The two outputs are highly correlated (R²2=0.988) and the relationship shows no deviation from linearity in the lower or higher range of attenuance values. It is found that over the full range of attenuance values (ca. 1-2 to 11-12 per metre) attenuance derived from the short pathlength transmissometer output is consistently higher than that derived from the medium pathlength transmissometer output (average offset: 1.01 ±0.12 per metre). Comparisons, carried out by the SPM Group, University of North Wales, Bangor, with calibrated attenuance data from the transmissometer moored close to the surface layer on POLRIG#A, suggested that the medium pathlength transmissometer was closer to the correct value.
• Oxygen: a decrease in the precision of the oxygen probe was noted during the cruise on 21/04/1999 and resulted in the replacement of the probe before cast 037. Although no obvious anomaly was noticed during the visual screening of the data series, users are advised to consider with caution data collected just before this cast.
• The absolute oxygen concentrations were very high giving rise to oxygen saturation levels of up to 180%. Although these may appear exceptionally high, the data originators confirmed that they were plausible for the area studied at times of high phytoplanktonic production (pers. comm. and Zindler et al. 2001).

Reference

Zindler JS, Baretta JW, Heins C, Hoogervorst RDN, Suijlen JM (2001) Non-turbulent dynamics and water column biology and physics. Report RIKZ/OS/2001.112X

Project Information

PROcesses of Vertical Exchange in Shelf Seas (PROVESS)

Introduction

PROVESS was an interdisciplinary study of the vertical fluxes of properties through the water column and the surface and bottom boundary layers. The project was funded by the European Community MAST-III programme (MAS3-CT97- 0159) and ran from March 1998 to May 2001.

Scientific Rationale

PROVESS was based on the integration of experimental, theoretical and modelling studies with the aim of improving understanding and quantification of vertical exchange processes in the water column, in particular in the surface and benthic boundary layers and across the> pycnocline. PROVESS also explored mechanisms of physical-biological coupling in which vertical exchanges and turbulence significantly affect the environmental conditions experienced by the biota with particular reference to aggregation, flocculation, sedimentation and trophic interactions.

Fieldwork

The experimental phase of the project was carried out at two contrasting sites in the North Sea: the northern North Sea site (NNS) and the southern North Sea site (SNS).

The two sites had the following characteristics:

At both locations measurements were concentrated at a central position with additional measurements being made to estimate horizontal gradients. Moored instruments (including current meters, temperature and pressure sensors, fluorometers, transmissometers, nutrient analysers and meteorological sensors) were deployed between 7 September and 5 November 1998 at the NNS and between 29 March and 25 May 1999 at the SNS. Each experiment was supported by intensive measurement series made from oceanographic ships and involving turbulence dissipation profiler CTD, particle size profilers, optical profilers, benthic sampling and water bottle sampling.

Details of the cruises were as follows:

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: