Metadata Report for BODC Series Reference Number 880676

• 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 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.

RV Belgica 9919 CTD Data Documentation

Instrumentation and Shipboard Procedures

The CTD profiles were taken with a SeaBird SBE09 plus system. The instrument was equipped with a sensor set comprising an SBE-3 temperature sensor and SBE-4 conductivity sensor. The system had a Temperature and Conductivity (TC) duct with an inertia-balanced pump flow, designed to improve the performance of the salinity measurements.

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 SeaBird optical backscatter sensor.

The CTD was periodically sent for calibration to SeaBird's NWRCC facility in Washington State. An average of 4 salinity samples were taken per cast, stored in crown-corked beer bottles, and determined on Guildline Portasal laboratory salinometer, calibrated using OSI standard seawater.

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 0.8 m above it.

Data Acquisition

The SeaBird SBE09 plus CTD system measured the depth of the sensor package, water temperature, conductivity, backscatter and dissolved oxygen at a rate of 24 samples per second. These data were averaged in the SeaBird deck unit over a 0.5-second interval. The resultant data were plotted on a VDU screen and used to decide water-sampling depths. The CTD software automatically marked the depths as part of the bottle firing sequence.

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.

Editing

The in-house graphics editor at BODC was used to mark the start and end of the downcasts, to remove noisy data logged whilst the instrument was stabilising.

The data were screened, point-by-point, and any obvious spikes were marked "suspect".

Once screened, the CTD downcasts were loaded into a database under the Oracle relational database management system. These were later migrated for inclusion in the National Oceanographic Databank.

Calibration

Pressure

The pressure calibrations were obtained by looking at the pressure values logged whilst the CTD unit was on the deck. Data were available from legs A and C. The mean of the corrections from these legs was used for leg B.

The following corrections were applied:

Temperature

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

Salinity

The salinity sensor was calibrated against discrete samples analysed using a Guildline Portasal Model 8410 laboratory salinometer. There was excellent agreement between the CTD and bottle data, with a mean difference of 0.001 PSU (N=67, SD=0.005). As this correction is statistically insignificant, no salinity calibration has been applied to the data.

Oxygen

There were serious problems with the CTD dissolved oxygen sensor on this cruise. This was particularly obvious during leg A, where the bottle data showed the surface dissolved oxygen concentration to vary between 248 and 254 µM, whereas the CTD data ranged from 245 to 299 µM. The following strategy was adopted to salvage as much data as possible whilst ensuring that no poor quality data remained in the final data set.

Leg A:
There was one deep cast with oxygen bottle data (05A) during leg A, which was calibrated using the equation:

The CTD oxygen data from all other casts on leg A were deleted from the data set.

Leg B:
The oxygen sensor was more stable on this leg than the previous leg. However, data from the following casts were rejected either because there were no oxygen bottle data or data check (e.g. oxygen minimum) or because there was serious disagreement between the CTD and bottle data:

11A, 11B, 11C, 13A, 24A, 25A, 26A, 29B, 29C, 30C, 33B, 38A, 39A, 40A, 44B, 45C.

The following calibration was obtained from the remaining casts and has been applied to the data:

Leg C:
None of the problems observed in the Leg A data were present in the data from this leg of the cruise. No data have been deleted and the following calibration has been applied to all CTD casts from this leg:

Optical Backscatter

The data were calibrated using the SeaBird software, based on a laboratory formazin calibration. No additional calibrations have been applied.

There is reason to query the data from casts taken on leg B after midday on 09/09/1999 and on leg C. The data values are exceptionally high and, more significantly, much higher at depth than at the surface. It is therefore recommended that these data be used with caution.

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).

Data Warnings

Some oxygen data have been deleted from the data set where the quality was questionable. However, the data that remain may be used with confidence.

The nephelometer data from the later part of leg B (after midday on 09/09/1999) and from leg C should be used with caution.

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.and 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

Fixed Station Information

OMEX II-II Repeat Section P

Section P was one of ten repeat sections sampled during the Ocean Margin EXchange (OMEX) II-II project between June 1997 and October 1999.

The CTD measurements collected at repeat section P, at the Iberian Margin, lie within a box bounded by co-ordinates 42° 30.7' N, 10° 20.0' W at the southwest corner and 42° 40.9' N, 09° 8.9' W at the northeast corner.

Cruises occupying section P

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: OMEX II-II Repeat Section P

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

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.