Metadata Report for BODC Series Reference Number 876296

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The SBE 13 instrument has been out of production since 2001 and has been superseded by the SBE 43.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

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.

FS Meteor 43_2 CTD Data Documentation

Instrumentation and Shipboard Procedures

The CTD profiles were taken with a SeaBird SBE 911 plus system. The instrument had enclosed conductivity and temperature sensors supplied with water by a pump. The water inlet was at the base of the bottle rosette.

When not in use, the sensors were bathed in MilliQ water. SeaBird temperature sensors are high performance, pressure protected thermistors. Other sensors on the rig were a dissolved oxygen cell (YSI SBE-13-Y polargraphic membrane) and a SeaTech red light transmissometer with a 25 cm path length.

The CTD was periodically sent for calibration to SeaBird's NWRCC facility in Washington State.

A SeaBird rosette sampler fitted with 12, 10-litre Niskin bottles was mounted above the frame. The bases of the bottles were level with the pressure sensor with their tops 0.75 m above it.

The standard operational procedure was to deploy the CTD to a depth of 10 m and leave it there until the pump had switched on and cleared the plumbing of bubbles. The instrument was then raised to the surface and the downcast commenced. However, during this cruise there was heavy swell combined with wind sea from a different direction and the ship rolled heavily when on station. Consequently, it was considered too risky to bring the instrument to the surface and the downcasts began at depths between 8 and 15 metres. There were also a small number of casts where additional downcast data were lost due to insufficient time being allowed for the system to equilibrate before lowering commenced.

The instrument was lowered continuously at approximately 1 m/s to the sea floor and then raised at the same rate in stages between bottle firing depths.

Data Acquisition

The CTD sampled at 24 Hz but this was automatically reduced to 3 Hz by the deck unit. The data were logged on a PC using the SeaBird SEASAVE program.

Post-Cruise Processing

The SeaBird DATCNV software was used to convert the binary raw data files into the calibrated ASCII data files supplied to BODC.

The salinity computation algorithm in the software is based on Fofonoff and Millard (1982). Salinity spiking on thermal gradients was minimised through software realignment of the temperature and conductivity channels.

Reformatting

The data were converted into the BODC internal format to allow the use of in-house software tools, notably the workstation graphics editor. In addition to reformatting, the transfer program converted the dissolved oxygen from µmol/kg to µM by multiplying the values by (1000 + sigma-theta)/1000. The data were loaded into the Oracle relational database management system and later migrated to the National Oceanographic Database.

Editing

Reformatted CTD data were transferred onto a high-speed graphics workstation for manual inspection using a custom in-house graphics editor. The top and bottom of the downcast were marked to eliminate noisy data logged whilst the instrument was stabilising.

The data were examined point by point and any obvious spikes were flagged 'suspect'.

Once screened on the workstation, the CTD downcasts were loaded into a database under the Oracle relational database management system. Note that the loader only included data from the downcast marked during screening.

Casts CTD23, CTD24 and CTD27 were particularly badly affected by a lack of downcast data, with virtually no temperature, salinity or oxygen in the top 100 m. Data were recovered whenever possible by patching in upcast values.

CTD31 was undertaken to collect water at a depth of 10 m, following a bottle problem on the previous cast. There were no usable downcast data. This was 'fixed' by patching in an upcast value. The water column was extremely well mixed allowing a constant value to be used.

Calibration

Pressure

The pressure calibrations were obtained by looking at the pressure values logged whilst the CTD unit was on the deck, which gave the following offset:

Temperature

The temperature data are believed to be accurate as supplied and no further calibrations have been applied.

Salinity

The salinity calibrations were derived by comparison of the values measured by the CTD with salinometer determinations on water bottle samples.

The following corrections have been applied to the data:

Dissolved Oxygen

The CTD dissolved oxygen data were calibrated against water sample data obtained by the University of Liège using an automated Winkler titration technique. The bottle data were converted to units of µM at in-situ temperature and salinity prior to calibration.

The following equation was derived and has been applied to the data:

Optical Attenuance

The SeaBird processing software included a source decay correction based on an initial air voltage of 4.664 (-0.001 V blocked) and current air voltage, taken in September 1997, of 4.658 volts (0.006 V blocked). However, measurements taken during the cruise indicated that the air voltage had dropped 4.597 volts (0.001 V blocked)

The data were brought into line with the cruise air reading data by subtracting 0.053 per m from the calibrated values generated by the SeaBird software. This reduced the clear water attenuance values from between 0.4 and 0.41 to a more credible range of 0.35 to 0.36.

Data Reduction

Once all screening and calibration procedures were completed, the data set was binned to 2 db (casts deeper than 100 db) or 1 db (casts shallower than 100 db). The binning algorithm excluded any data points flagged suspect and attempted linear interpolation over gaps up to 3 bins wide. If any gaps larger than this were encountered, the data in the gaps were set null.

Downcast values corresponding to the bottle firing depths were incorporated into the database. Oxygen saturations were computed using the algorithm of Benson and Krause (1984).

References

Benson B.B. and Krause D. jnr. 1984. The concentration and isotopic fractionation of oxygen dissolved in fresh water and seawater in equilibrium with the atmosphere. Limnol. Oceanogr. 29, pp.620-632.

Fofonoff N.P., Millard R.C. 1982. Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science. 44.

Project Information

Ocean Margin EXchange (OMEX) II - II

Introduction

OMEX was a European multidisciplinary oceanographic research project that studied and quantified the exchange processes of carbon and associated elements between the continental shelf of western Europe and the open Atlantic Ocean. The project ran in two phases known as OMEX I (1993-1996) and OMEX II - II (1997-2000), with a bridging phase OMEX II - I (1996-1997). The project was supported by the European Union under the second and third phases of its MArine Science and Technology Programme (MAST) through contracts MAS2-CT93-0069 and MAS3-CT97-0076. It was led by Professor Roland Wollast from Université Libre de Bruxelles, Belgium and involved more than 100 scientists from 10 European countries.

Scientific Objectives

The aim of the Ocean Margin EXchange (OMEX) project was to gain a better understanding of the physical, chemical and biological processes occurring at the ocean margins in order to quantify fluxes of energy and matter (carbon, nutrients and other trace elements) across this boundary. The research culminated in the development of quantitative budgets for the areas studied using an approach based on both field measurements and modeling.

OMEX II - II (1997-2000)

The second phase of OMEX concentrated exclusively on the Iberian Margin, although RV Belgica did make some measurements on La Chapelle Bank whilst on passage to Zeebrugge. This is a narrow-shelf environment, which contrasts sharply with the broad shelf adjacent to the Goban Spur. This phase of the project was also strongly multidisciplinary in approach, covering physics, chemistry, biology and geology.

There were a total of 33 OMEX II - II research cruises, plus 23 CPR tows, most of which were instrumented. Some of these cruises took place before the official project start date of June 1997.

Data Availability

Field data collected during OMEX II - II have been published by BODC as a CD-ROM product, entitled:

• OMEX II Project Data Set (three discs)

Further descriptions of this product and order forms may be found on the BODC web site.

The data are also held in BODC's databases and subsets may be obtained by request from BODC.

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: