Metadata Report for BODC Series Reference Number 888875

• 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

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Specifications

These specification apply to the MK3C version.

Further details can be found in the specification sheet.

RV Thalassa 1099 CTD Data Documentation

Instrumentation and Shipboard Procedures

The CTD profiles were taken with a Neil Brown Systems Mk IIIB CTD including pressure, conductivity, temperature and dissolved oxygen sensors. A fluorometer and a transmissometer (type and path length unknown) were also included in the CTD package. A 24-position General Oceanics rosette with 12-litre Niskin bottles was fitted to the CTD frame to collect water samples.

Data Acquisition and On-board Processing

The data supplied to BODC conformed to the expected output format from the standard EG&G acquisition and processing software used with Neil Brown instruments. The data were supplied as 1-decibar binned values, labelled with the pressures of the midpoints of the bins. The transmissometer values were obviously raw voltages. The data from ST0898 included fluorometer data in the form of nominal chlorophyll concentrations. It has been assumed that the data from this cruise are also supplied as nominal chlorophyll concentrations.

Post-cruise Processing

Reformatting and Editing

The data were supplied to BODC as ASCII files, which were converted into the BODC internal format. Each profile was examined using an in-house graphical editing tool and any spikes observed in the data were flagged as suspect. Flags were also applied to the cycle number channel that indicated the start and end of the profile downcast. Twenty five screened downcasts were loaded into the Oracle relational database management system. These were later migrated to the National Oceanographic Database.

Calibration

Pressure

No air-logged data were included in the data set. Consequently, the accuracy of the originator's pressure calibration could not be checked. The instrument was reported as calibrated in June 1999. There was no evidence of significant errors in the pressure values.

Temperature

No reversing thermometer data were available and consequently the originator's calibration could not be checked. The instrument was reported as calibrated in June 1999. There was no evidence of significant errors in the temperature values.

Salinity

No salinity sample data were taken on this cruise. However, a calibration data set, based on Autosal bottle salinity determinations, was made available from the second (non-OMEX) leg of this cruise. The overall calibration for this cruise leg was an offset of -0.044 (N=42, SD=0.020). This calibration has been applied to the data.

There is strong evidence from this calibration data set of drift in the CTD conductivity sensor, which can be seen in the variation of the individual cast calibrations:

The uncertainty in the calibration is relatively high, so the data from this cruise should not be used for applications that require top quality data. However, the calibration quantifies the accuracy of the data and consequently they may be used with confidence for some purposes.

Note that the deepest cast from this cruise was 500m. Consequently, theta-salinity plots couldn't be used to improve the quality of the salinity calibration.

Attenuance

The data supplied had values in the range 4.38 to 4.82, which are the values one would associate with transmissometer output values. Inspection of the data showed that the high values were associated with 'clear water', which confirmed that the data were voltages and not attenuance values.

The optical path length of the transmissometer was not supplied with the data. A simple modelling exercise showed that the only path length out of 5, 10, 20, 25 and 100 cm that gave anything like sensible attenuance values was 10cm. Consequently, a 10cm path length was assumed and the following equation was used to convert voltage to attenuance:

This resulted in attenuance values spanning the range from 0.375 to 1.541, which are of the correct order of magnitude for the OMEX II box.

No air correction data were available. A nominal air correction of -0.025 per metre was applied to the data, normalising the data to a clear water minimum value of 0.35 per m.

The data from the deep (500m) casts show a trend of increasing attenuance at depth as the cruise progresses. This is believed to be an artefact, but no attempt has been made to correct it.

Oxygen

There were no oxygen bottle data from this cruise. Normal BODC practice in such cases is to delete the CTD oxygen data from the data set. However, visual examination of the data gave the overall impression that the profiles were reasonable and it was considered worthwhile to produce a qualitative data set.

The data supplied were obviously not in any meaningful units, with data values in the region of 2. Such out of range values can cause all sorts of problems for any bespoke software that is more used to conventional oxygen concentrations. Consequently, the data were scaled to bring them into reasonable range. A scaling factor of 109.6 (based on normalising the data at 500m to data at the same depth from Belgica cruise BG9919) was used, which produces surface saturations in the range 90-100%.

Users should be under no illusion about these data. They are NOT calibrated and should be used for QUALITATIVE purposes only.

Chlorophyll

The only extracted chlorophyll data set available for this cruise was size-fractionated chlorophyll-a data from a trichromatic spectrophotometric assay. The fluorometer values were regressed against the summed size-fraction values, resulting in the following calibration equation:

This has been applied to the data.

Data Binning

The final data set has been binned to give a resolution of 1 decibar.

Warnings

The salinity data should not be used in high accuracy applications because there is strong evidence for drift between casts of up to 0.02 PSU.

The dissolved oxygen data are NOT calibrated. They should only be used qualitatively.

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 N

Section N 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 N, at the Iberian Margin, lie within a box bounded by co-ordinates 42° 58.2' N, 10° 19.9' W at the southwest corner and 43° 5.3' N, 09° 17.9' W at the northeast corner.

Cruises occupying section N

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 N

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.