Metadata Report for BODC Series Reference Number 1014620

• 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.

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.

SeaTech Transmissometer

Introduction

The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.

Specifications

• Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
• Beam diameter: 15 mm
• Transmitted beam collimation: <3 milliradians
• Receiver acceptance angle (in water): <18 milliradians
• Light source wavelength: usually (but not exclusively) 660 nm (red light)

Notes

The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

Further details can be found in the manufacturer's Manual.

RRS Discovery 223 CTD Data Documentation

Introduction

CTD profile data are presented from the Vivaldi '96 cruise Discovery 223, as reported by Leach & Pollard et al. (1998).

Instrumentation and Methodology

Instrumentation Summary

The CTD profiles were taken with a Neil Brown Systems MkIIIb CTD (SOC modified) Deep01 mounted beneath a bottle rosette. The CTD was fitted with a pressure sensor, conductivity cell, platinum resistance thermometer, a Beckman dissolved oxygen sensor, a Chelsea Instruments Aquatracka MkIII fluorometer, a Sea Tech 100cm Transmissometer, a new 25cm pathlength Chelsea Instruments Alphatracka MkII Transmissometer, an SOC/Valeport Ultraviolet Nitrate Sensor, a Simrad altimeter (model 807-200m) and an IOSDL 10 Khz pinger.

Data Acquisition

Lowering rates for the CTD package were generally in the range 0.5-1.0ms^-1 but could be up to 1.5ms^-1. CTD data were logged at 16 frames per second. The CTD deck unit passes raw data to a dedicated Level A microcomputer where 1 second averages are assembled. During this process the Level A calculates the rate of change of temperature and a median sorting routine detects and removes pressure spikes. These data are sent to the Level B for archival. The data are then passed to a Level C workstation for conversion to Pstar format and calibration.

A total of 88 stations were occupied (12931 - 13018). Stations 12939, 12959, and 12973 were aborted due to bad weather.

Data Processing

The 1 second data passed to the Level C were converted to Pstar format and initially calibrated with coefficients from laboratory calibrations followed by a number of calibration corrections. The up and down cast data were extracted for merging with the bottle firing codes, thus the CTD variables were reconciled with the bottle samples. Final calibrations were applied using the sample bottle data. Finally, down cast data were extracted but not sorted on pressure or averaged to 2db values.

The data were worked up to WOCE standards by the data originators before being supplied to BODC.

BODC Data Processing

No further calibrations were applied to the data received by BODC. BODC were mainly concerned with the screening and banking of the data.

The CTD data were received as 1Hz, but not pressure sorted, down cast data. Parameters were pressure (dbar), temperature (°C), salinity (psu), oxygen (µmol/l), chlorophyll-a (mg/m³) and Sea Tech transmittance (/m). Nitrate sensor data (att240, att220 and att300) were also received in the data files but were ignored. Stations 12931, 12932 and 13016 do not have calibrated oxygen. The chlorophyll data are fully calibrated except for stations 12931 and 12932.

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the graphics editor. Attenuance was calculated as 1*log(transmittance), assuming a pathlength of 1 metre.

Spikes in the data were manually flagged 'suspect' by modification of the associated quality control flag. In this way none of the original data values were edited or deleted during quality control.

Attenuance is null from station 12974 to 13018 due to the Sea Tech instrument being removed after enough data had been acquired for comparative purposes with the new Chelsea transmissometer.

The temperature, salinity and oxygen data from cruise DI223 required little flagging and just a few points were set suspect. The fluorometer and oxygen data are null for station 12990. Lots of bad Sea Tech attenuance data were flagged suspect.

Once screened, the CTD data were loaded into a database under the Oracle relational database management system. The start time stored in the database is the CTD deployment time, and the end time is the time the CTD was removed from the water. Actually these times are more precisely the start and end of data logging. Latitude and longitude are the mean positions between the start and end times calculated from the master navigation in the binary merged file.

References

Leach, H. & Pollard, R.T. et al. (1998). RRS Discovery Cruise 223. Southampton Oceanography Centre, Cruise Report No. 17, 68pp.

Project Information

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:

• Goal 1. To develop models to predict climate and to collect the data necessary to test them.

• Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.

UK WOCE

The UK made a substantial contribution to the international World Ocean Circulation Experiment (WOCE) project by focusing on two important regions:

1. Southern Ocean - links all the worlds oceans, controlling global climate.
2. North Atlantic - directly affects the climate of Europe.

A major part of the UK effort was in the Southern Ocean and work included:

• Two surveys, in the South Atlantic as part of the WOCE Hydrographic Programme.
• SWINDEX, a year long study of the Antarctic Circumpolar Current (ACC) where it crosses major topography south of Africa.
• ADOX, a study of deep water flow from the Atlantic to the Indian Ocean.
• ACCLAIM, a study of the ACC by altimetry and island measurements.

In the North Atlantic the UK undertook:

• NATRE, a purposeful tracer experiment to look at cross isopycnic processes.
• CONVEX, a study of the deep ocean circulation and its changes.
• VIVALDI, a seven year programme of seasonally repeated surveys to study the upper ocean.
• Long-term observations of ocean climate in the North West Approaches.

Satellite ocean surface topography, temperature and wind data were merged with in situ observations and models to create a complete description of ocean circulation, eddy motion and the way the ocean is driven by the atmosphere.

The surveys were forerunners to the international Global Ocean Observing System (GOOS). GOOS was later established to monitor annual to decadal changes in ocean circulation and heat storage which are vital in the prediction of climate change.

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Extended Ellett Line

The Extended Ellett Line is a hydrographic transect consisting of 64 individual fixed stations which have been occupied, typically on an annual basis, since September 1996. The Line runs from the south of Iceland, across the Iceland Basin to the outcrop of Rockall, and across the Rockall Trough to the north west coast of Scotland (see map). CTD dips and associated water sampling for the analysis of nutrients are routinely performed during each station occupation.

The Extended Ellett Line augments the original Ellett Line time series - a shorter repeated transect which encompassed those stations between Rockall and Scotland. Work on the Ellett Line was typically carried out at least once a year between 1975 and 1996.

Map of standard stations (1996-present)

Map produced using the GEBCO Digital Atlas

The white triangles indicate the nominal positions of the Extended Ellett Line stations visited since September 1996. Measurements made along the Extended Ellett Line lie within a box bounded by co-ordinates 56° N, 21° W at the south west corner and 65° N, 6° W at the north east corner.

Nominal Extended Ellett Line stations (September 1996-present)

Listed below are nominal details of the standard hydrographic stations that form the Extended Ellett Line. The majority of these stations have been sampled since the outset, although several have been added more recently.

Occupations of the Extended Ellett Line (September 1996-present)

* These cruises only surveyed the original hydrographic section between Scotland and Rockall.

Related Fixed Station activities are detailed in Appendix 1

Fixed Station Information

World Ocean Circulation Experiment (WOCE) Atlantic Area 12 (AR12)

WOCE was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate. WOCE established numerous areas and repeat sections in the Atlantic Ocean as illustrated in the map below.

AR12 spans the boundary between the subtropical and subpolar gyres in the eastern basin; stations lie within a box bounded by 40.0°N, 35.0°W at the southwest corner and 65.0°N, 03.0°W at the northeast corner The area was occupied between April 1991 to September 1998. A table of all AR12 cruises is presented below:

Related Fixed Station activities are detailed in Appendix 2

Fixed Station Information

Ellett Line

The Ellett Line is a hydrographic transect consisting of 35 individual fixed stations which were occupied, usually at least once a year, between 1975 and 1996. The time series is named after the scientist David Ellett, who coordinated the survey work at Dunstaffnage Marine Laboratory (DML), near Oban. The transect ran between the north west coast of Scotland to the small outcrop of Rockall, via the Anton Dohrn Seamount - a prominent bathymetric feature in the Rockall Trough (see map). STD/CTD dips and associated water sampling for the analysis of nutrients were routinely performed during each station occupation.

In 1996 the transect was lengthened to incorporate new additional fixed stations crossing the Iceland Basin from Rockall to Iceland. This transect, which is still routinely occupied annually, is now known as the Extended Ellett Line and is a collaborative effort between scientists at Dunstaffnage Marine Laboratory and the Southampton site of the National Oceanography Centre (NOC).

Map of standard stations (1975-1996)

Map produced using the GEBCO Digital Atlas

The white triangles indicate the nominal positions of the Ellett Line stations (1975- 1996). Measurements made along the Ellett Line lie within a box bounded by co-ordinates 56° 40.02' N, 13° 42.0' W at the south west corner and 57° 37.2' N, 6° 7.98' W at the north east corner.

Nominal Ellett Line stations (1975-1996)

Listed below are nominal details of the standard hydrographic stations that formed the Ellett Line between 1975 and January 1996.

History of Ellett Line occupations (1975-January 1996)

Related Fixed Station activities are detailed in Appendix 3

Fixed Station Information

Ellett Line/Extended Ellett Line: Station M

Station M is one of the fixed CTD stations, which together form The Extended Ellett Line. The line lies between Iceland and the Sound of Mull (Scotland) crossing the Iceland Basin and Rockall Trough via the outcrop of Rockall. As part of this initiative, CTD dips, together with associated discrete sampling of the water column, have typically been carried out annually at this station since September 1996.

Prior to September 1996, Station M was part of a shorter repeated survey section, consisting of 35 fixed stations, known as The Ellett Line (originally termed the Anton Dohrn Seamount Section). This line incorporated those stations across the Rockall Trough and Scottish shelf between Rockall and the Sound of Mull and was visited at regular intervals (usually at least once a year) between 1975 and January 1996.

Related Fixed Station activities are detailed in Appendix 4

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: Extended Ellett Line

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

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