Metadata Report for BODC Series Reference Number 1022797

• 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 Dissolved Oxygen Sensor SBE 43 and SBE 43F

The SBE 43 is a dissolved oxygen sensor designed for marine applications. It incorporates a high-performance Clark polarographic membrane with a pump that continuously plumbs water through it, preventing algal growth and the development of anoxic conditions when the sensor is taking measurements.

Two configurations are available: SBE 43 produces a voltage output and can be incorporated with any Sea-Bird CTD that accepts input from a 0-5 volt auxiliary sensor, while the SBE 43F produces a frequency output and can be integrated with an SBE 52-MP (Moored Profiler CTD) or used for OEM applications. The specifications below are common to both.

Specifications

Further details can be found in the manufacturer's specification sheet.

Instrumentation

CTD and auxiliary sensors

The CTD used on JC029 consisted of a 24-way stainless steel frame with the following instruments attached.

A complete spare CTD suite including instruments was available for use but was not required.

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.

BODC processing

Data from the pressure, temperature, conductivity and oxygen sensors were submitted to BODC in one Matlab .mat file that included 2 dbar averaged profiles from the standard CTD stations. Data from the other auxiliary sensors (transmissometer, fluorometer and backscatter sensor) were not included in this dataset as the originators had not produced 2 dbar averaged profiles. Those data were processed by BODC independently and are described in a separate document.

In order to ingest the CTD profiles into the BODC system, 61 individual files were generated, one for each cast (e.g., CTD04, CTD06 etc). The data were transferred to NetCDF format using BODC generated Matlab code. This involves mapping each of the originator's variables to a BODC parameter code. The table below shows the parameter mapping.

The data were screened using BODC in-house visualisation software. Any suspect data points were flagged with the appropriate BODC quality control flag

Originator's data processing

Sixty six Conductivity-Temperature-Depth (CTD) casts were performed during cruise JC029. These included three test casts (only one was submitted to BODC), two tow-yo casts and 61 standard casts. CTD stations were occupied along various transects around the study area which was located to the North of the Kerguelen Islands in the Indian Ocean.

Initial data processing of the raw CTD data was performed on a PC using the Sea-Bird processing software SBE Data Processing, Version 7.18. The data were processed using the following modules in the order given below:

• Data conversion
• Align CTD
• Cell Thermal Mass
• Filter
• Loop Edit
• Derive
• SeaPlot

Calibrations

Manufacturers' calibrations were applied to all sensors prior to data collection and post-cruise calibration of the CTD conductivity sensors with bottle salinity samples was undertaken using a suite of Fortran and Matlab programs. No independent measurements were collected for calibration of any other sensors.

The calibration of the primary and secondary conductivity sensors involved comparison of 10-second burst average upcast CTD data from bottle firing depths with salinities obtained from water sample analyses. The conductivity calibration followed the method of Millard and Young (1993). For groups of consecutive stations, a conductivity slope and bias term are found to fit the CTD conductivity; a linear station-dependent slope correction is applied to account for calibration drift of the CTD conductivity cell. Data from the entire cast are used to determine the conductivity calibration.

The calibration coefficients were then applied to the entire CTD salinity dataset and 2 dbar averaged salinity, conductivity, temperature and oxygen data were produced from the downcast data. The remaining auxiliary sensors (transmissometer, fluorometer and backscatter sensor) were not included in the 2 dbar averaged dataset.

The discrete salinity samples used for the CTD calibration were analysed with a Guildline Instrument LTD autosal 8400B salinometer serial number 68426 which was kept in a temperature controlled lab and operated at 20 - 21^oC. The salinometer was equipped with an Ocean Scientific International Ltd (OSIL) peristaltic pump.

Calibration of both the primary and secondary sensor were completed. For the primary sensor a standard deviation of 9.68 x 10^-4 was achieved. It is known that the secondary sensor was unreliable so both the profile data and the calibrations for that sensor were discarded.

More information on the CTD on-board processing can be found on page 41 of the cruise report, with the CTD calibration detailed on page 44, which is accessible through the JC029 metadata Report.

Project Information

Southern Ocean FINEStructure (SOFINE) project document

The Southern Ocean FINEStructure (SOFINE) project was a UK field programme aimed at studying the frictional processes that slow down the Antarctic Circumpolar Current (ACC) and influence the meridional exchange of water masses in the Southern Ocean.

The study investigated the role of sea floor topography in slowing the ACC and driving meridional flow across the Southern Ocean, and the manner in which mesoscale and small scale oceanic phenomena modified water mass properties and affected their movement across the ACC. Specifically, SOFINE set out to:

• Determine the relative importance of oceanic processes associated with large scale (hundreds to thousands of kilometres) and small scale (a few kilometres) sea floor topography in the context of ACC flow rates and water mass exchange.
• Identify the oceanic processes controlling the rate at which water masses are transformed and fluxed across the ACC.

The SOFINE experiment focused on a major meander of the ACC around the northern Kerguelen Plateau in the Indian Ocean. Theories and models of Southern Ocean circulation indicated that this region experienced intensified 'friction' and cross-ACC flow. Fieldwork was undertaken over a 52 day period in November and December 2008, and included hydrographic observations, microcstructure and turbulence measurements, detailed bathymetric surveys and several deployments of floats, drifters and moorings.

SOFINE was funded by the UK Natural Environment Research Council and involved the collaboration of a number of international institutions: the National Oceanography Centre (UK), the University of East Anglia (UK), British Antarctic Survey (UK), Woods Hole Oceanographic Institution (US), the Commonwealth Scientific and Industrial Research Organisation (Australia), the University of Tasmania (Australia) and the Leibniz Institute of Marine Sciences (IFM-GEOMAR) at the University of Kiel (Germany).

For more information please see the official project website at SOFINE

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: