Metadata Report for BODC Series Reference Number 888501

• 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 Professor Shtokman 0898 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 was 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. All available information indicates that the raw chlorophyll channel supplied was directly proportional to the chlorophyll concentration. It is not known whether this was from an instrument with a linear response or if it was nominally calibrated data from a logarithmic-response instrument.

Post-cruise Processing

Reformatting and Editing

The data were supplied to BODC as ASCII files, which were converted into the BODC internal format. The reformatting program converted the units of the dissolved oxygen data from ml/l to µM through multiplication by 44.66.

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 three 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 March 1998. 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 March 1998. There was no evidence of significant errors in the temperature values.

Salinity

The salinity data were calibrated against a set of 25 samples taken from two stations and analysed by salinometer. However, the samples were stored for 12 months prior to analysis, which inevitably means a high probability of errors caused by evaporation loss.

The resulting offset of -0.104 (N=25, SD=0.062) was applied to the data. This calibration gave cause for concern for two reasons. First, the absolute value was unusually large, especially for a recently calibrated instrument. Secondly, the standard deviation was alarmingly large, probably due to the poor quality of the bottle data set. However, there is reason to believe that the accuracy of the calibrated data is better than the statistics indicate. The deep (theta<10) theta-salinity curves from this cruise agreed within 0.02 PSU with data of known good quality (cruise CD105B), which were collected in the vicinity a year earlier. The uncorrected Shtokman salinity data were also reported to be up to 1 PSU high with respect to the regional climatology.

However, users should bear in mind the quality limitations of the calibration data if high accuracy salinity data are required.

Oxygen

The CTD oxygen data were calibrated against a bottle data set taken by the University of Vigo. The calibration was difficult because the CTD oxygen sensor was obviously drifting but samples were only available for 7 of the 22 casts and only in the upper 200 metres. The problem was exacerbated because the sensor was slow to equilibrate on some casts, which resulted in further calibration data loss.

Three calibration equations were produced:

These calibrations have been applied to the data. Users should be aware that the R² values flatter the calibration quality and are advised to use the absolute calibrated values with caution. The data are believed to be more accurate in the upper 200 m and there is significantly lower confidence in the calibration for CTD11 to CTD21 because of the high values (225-228 µM) produced for the oxygen minimum. The expected value, based on other OMEX II cruises, is 190 µM.

The data values for CTD23 were clearly in error (surface saturation of 182% using the CTD22 calibration) and have been deleted from the data set.

Chlorophyll

The data originator provided the following fluorometer calibration equation:

This was based on a set of acetone-extracted chlorophyll data assayed fluorometrically, using a Turner Designs bench fluorometer. The calibration has been applied to the data.

Data Binning

The final data set has been binned to give a resolution of 2 decibars. The manner in which the input data had been binned means that each binned value in the data set is effectively the average of one bin above and one bin below the pressure label on the output bin. For example, the output bin labelled 1 decibar is the average from the input bins labelled 0.5 and 1.5 decibars.

Warnings

The oxygen calibration for this cruise was difficult and users are advised to treat the absolute CTD oxygen concentrations with caution, particularly for CTDs 11 to 21.

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.