Metadata Report for BODC Series Reference Number 1774796
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Open Data supplied by Natural Environment Research Council (NERC)
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Instrument Description for ES031, ES038, ES048 CTD
CTD Unit and Auxiliary Sensors
The CTD unit comprised a Sea-Bird Electronics 911plus with two pairs of temperature and conductivity sensors and a SBE43 oxygen sensor. The CTD frame also incorporated a Tritech altimeter.
A rosette sampling system equipped with 12-10 l General Oceanics sampling bottles was used to collect samples for oxygen isotopes and salinity measurements.
|Temperature||SBE3 plus|| |
2705, 2679: for casts 1 to 110
2705 and 4235: from cast 111 onwards
|Conductivity||SBE4 plus||2222 and 2248|
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.
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.
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 for the SBE 9 plus underwater unit are listed below:
|Parameter||Range||Initial accuracy||Resolution at 24 Hz||Response time|
|Temperature||-5 to 35°C||0.001°C||0.0002°C||0.065 sec|
|Conductivity||0 to 7 S m-1||0.0003 S m-1||0.00004 S m-1||0.065 sec (pumped)|
|Pressure||0 to full scale (1400, 2000, 4200, 6800 or 10500 m)||0.015% of full scale||0.001% of full scale||0.015 sec|
Further details can be found in the manufacturer's specification sheet.
BODC processing of Ernest Shackleton Cruise ES031, ES038, ES048 CTD Data
The data were sent to BODC as fully processed and calibrated casts. The originator's variables were matched against BODC codes and all data was transferred to BODC internal format, a subset of netcdf. There was no need to apply for unit conversions as originator's parameters were identical to the ones used on the BODC vocabulary.
|Originator's Parameter Name||Units||Description||BODC Parameter Code||Units||Comments|
|Temperature||°C||Temperature of the water body by CTD or STD||TEMPST01||°C||-|
|Salinity||-||Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm||PSALST01||-||Generated by Sea-Bird software from CTD temperature and conductivity data|
|-||-||Sigma-theta||SIGTPR01||kg m-3||Generated at BODC using the Fofonoff and Millard (1982) algorithm|
|-||-||Potential temperature||POTMCV01||°C||Generated by BODC using UNESCO Report 38 (1981) algorithm with parameters PSALST01 and TEMPST01|
|-||-||Conversion factor (volume to mass)||TOKGPR01||°C||Generated by BODC using SIGTPR01|
Reformatted CTD data were visually screened using the in-house editor EDSERPLO. No data values were edited or deleted. Flagging was achieved by modification of the associated quality control flag to 'M' for suspect values and 'N' for nulls.
Originator's processing document for Ernest Shackleton Cruise ES031, ES038, ES048
Originator's Data Processing
A total of 117 CTD casts were performed throughout the cruise. Preventive measures to protect against ice forming on the sensors were in place, but despite the efforts, the SBE43 gave spurious values after freezing up. Both temperature sensors had to be replaced as they failed just before the last casts. The altimeter did not work properly throughout the cruise.
Salinity samples were collected in 200 ml bottles and sealed with a rubber cap, which was held in place with a crimped foil. These were used to calibrate the CTD data. The oxygen isotopes samples were collected in 20 ml bottles using the same sealing mechanism as described above.
The originator applied quality control procedures to the casts resulting in several cycles being assigned a Null flag at the start or end of the cast.
Benson, BB and Krause, D., 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr., 29(3), 620-632
Fofonoff, NP and Millard, RC., 1983. Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science No. 44, 53pp.
UNESCO, 1981. Background papers and supporting data on the International Equation of State of Seawater 1980. UNESCO Technical Papers in Marine Science No. 38, 192pp
Global Science in an Antarctic Context (GSAC)
GSAC is the British Antarctic Survey research programme from 2005 to 2009, it encompasses 8 programmes, including 18 projects as well as long-term monitoring and survey activities.
This programme was created to fulfill BAS vision of becoming, by 2012, the leading international centre making use of the of the Antarctic and the Southern Ocean. This research programme consists of an integrated set of inter-disciplinary research, monitoring and survey activities designed to extract new knowledge from the Antarctic, provide information to policy makers and benefit society in general.
GSAC supports the Natural Environment Research Council (NERC) strategy Science for a Sustainable Future and contributes to other programmes such as the World Climate Research programme, the International Geosphere-Biosphere Programme, the Convention on Biological Diversity, the Scientific Committee for Antarctic Research and the International Polar Year 2007-2009.
The programme's components are highly interconnected and its content makes full use of BAS Antarctic infrastructure and builds on previous BAS research, survey and monitoring, whilst also exploring new areas.
The programmes contributing to GSAC are:
- ACES- Antarctic Climate and the Earth System
- BIOFLAME- Biodiversity, Function, limits and Adaptation from Molecules to Ecosystems
- CACHE- Climate and Chemistry: Forcings, Feedbacks and Phasings in the Earth System
- COMPLEXITY- Natural Complexity Programme
- DISCOVERY 2010- Integrating Southern Ocean Ecosystems into the Earth System
- GEACEP- Greenhouse to Ice-House Evolution of the Antarctic Cryosphere and Paleoenvironment
- GRADES- Glacial Retreat in Antarctica and Deglatiation of the Earth System
- SEC- Sun Earth Connections
- LTMS- Long Term Monitoring and Survey
More detail is provided in each programme document.
ACES- Antarctic Climate and the Earth System
This project is part of the BAS GSAC five year research programme. It was funded by NERC and extended from 2005 to 2009.
ACES aims to investigate the atmospheric and oceanic links that connect the climate of the Antarctic to that of lower latitudes, and their controlling mechanisms. Specific research topics include the formation and properties of Antarctic clouds, the complexities of the atmospheric boundary layer and the importance to the global ocean circulation of cold, dense water masses generated in the Antarctic.
Data will be collected by a comprehensive programme of oceanographic measurements from BAS ships in the Weddell and Bellingshausen Seas and by the Twin Otter aircraft, which will allow for the study of cloud microphysics and air-sea-ice interaction. An ice core will be collected from the southwestern Antarctic Peninsula and will give a 150-year record of the strength of the circumpolar westerly winds. This data will be used to test and improve global climate models and a new regional atmosphere-ice-ocean model for the Antarctic.
ACES has two components: ACES-FOCAS (Forcings from the Ocean, Clouds, Atmosphere and Sea-ice) and ACES-ACCENT (Antarctic Climate Change and Nonlinear Teleconnections). It also links with several other projects: CACHE, GRADES, GEACEP, BIOFLAME, DISCOVERY2010 and SEC.
The main objectives are:
- Understand the interactions between atmosphere, sea-ice and ocean at high southern latitudes
- Develop models to aid our understanding of Antarctic regional processes and enable the representation of essential regional phenomena in global models covering both the atmosphere and ocean
- Determine the nature and influence of the principal connections between Antarctica and the global climate system
- Determine the importance of water masses of Antarctic origin in the global ocean circulation
- Determine the sensitivity of the global climate system to processes occurring or originating in the Antarctic
Data sets collected during this project are available to the academic community.
Acronyms used in this text:
BAS- British Antarctic Survey
GSAC- Global Science in an Antarctic ContextNERC- Natural Environment Research Council
CACHE- Climate and Chemistry: forcings , feedbacks and phasings in the Earth System
GRADES- Glacial retreat in Antarctica and Deglaciation of the Earth System
GEACEP- Greenhouse to ice-house: Evolution of the Antarctic Cryosphere and Paleoenvironment
BIOFLAME- Biodiversity, Function, Limits and Adaptation from Molecules to Ecosystems
DISCOVERY2010- Integrating Southern Ocean Ecosystems into the Earth System
SEC- Sun Earth Connections Programme
|Cruise Name||ES20070116 (ES031, ES038, ES048)|
|Principal Scientist(s)||Keith Nicholls (British Antarctic Survey)|
|Ship||RRS Ernest Shackleton|
Complete Cruise Metadata Report is available here
No Fixed Station Information held for the Series
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||Below detection limit|
|>||In excess of quoted value|
|A||Taxonomic flag for affinis (aff.)|
|B||Beginning of CTD Down/Up Cast|
|C||Taxonomic flag for confer (cf.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|I||Taxonomic flag for single species (sp.)|
|K||Improbable value - unknown quality control source|
|L||Improbable value - originator's quality control|
|M||Improbable value - BODC quality control|
|O||Improbable value - user quality control|
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|