Metadata Report for BODC Series Reference Number 1628578

• 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

Open 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.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

Instrument Description

CTD Unit and Auxiliary Sensors

Until January 2003, CTD casts were undertaken by a Chelsea Instruments Aquapack. A single titanium housing contained all sensors (temperature, conductivity, pressure and fluorescence) sensor processing boards, transmission and data logger plus the internal batteries. A LiCor PAR (photosynthetic active radiation) sensor (serial number: 6387) was attached. Pressure certification of the sensors limited profiles to a depth of 200m. All data were logged internally.

Since 2003, a SeaBird 19plus SEACAT profiler (SeaBird Electronics, Inc) has been employed at the RaTS station. A self powered (powered by 9 D-size alkaline batteries) and self contained unit containing temperature, conductivity and pressure sensors together with a WetLabs in-line fluorometer and the same PAR sensor as used previously (LiCor; serial number: 6387). Utilisation of this instrument enabled full depth profiles to be conducted. Data from all sensors are logged internally, with data collection being initiated by a seawater switch.

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

The data arrived at BODC in Matlab binary .MAT files representing the CTD data collected as part of the Rothera Oceanographic and Biological Time Series (RaTS). These were reformatted to the internal QXF format using established BODC procedures. The following table shows how the variables within the matlab files were mapped to appropriate BODC parameter codes:

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag

Field Calibrations

Precision of the CTD was maintained by performing concurrent casts with SeaBird 911plus CTDs during regular visits of the RRS James Clark Ross and RV Laurence M. Gould to Rothera. SeaBird salinity data were themselves calibrated using discrete samples measured on a GuildLine Autosal 8400B salinometer, standardised with IAPSO p-series standard seawater (seawater standard of precisely known electrical conductivity ratio). Offsets to the RaTS salinity data were applied to reconcile them with the calibrated SeaBird data. Densities were calculated using the UNESCO (1983) algorithm.

Sampling strategy

Sampling began at the Rothera Oceanographic and Biological Time Series (RaTS) site in January 1997 which was subsequently occupied every five days during the summer and every seven days in the winter, except when weather, ice or logistic constraints intervened. An upper ocean hydrographic cast and discrete water sample at a depth of 15m was conducted. CTD (conductivity, temperature and depth) casts were made off an inflatable boat by use of a hand-cranked winch during the summer months and through a hole in the ice during the southern hemisphere winter. Discrete water samples were taken from a 15m depth using a Niskin bottle closed with a brass messenger. Water samples collected were measured for macronutrients (nitrate, nitrite, phosphate, ammonia and silicate), chlorophyll (both whole and size fractionated), dissolved oxygen isotopes, dissolved organic carbon and microbial community analysis. Prior to March 2002 all macronutrients were transported back to the laboratory at Rothera in the dark and analysed there. Since then, all silicate, phosphate, nitrite and nitrate samples have been preserved and sent to Ocean Scientific International Ltd, Petersfield, Hampshire, UK for analysis. Ammonium remains to be analysed at Rothera. Samples collected for oxygen isotopic analysis were sent annually (4^oC; dark) to the Natural Environment Research Council Isotope Geosciences Laboratory, Keyworth, UK.

There are two extended periods during which no data could be collected. August to December in both 2000 and 2001. In 2000, there was an unusually extended period of unfavourable ice conditions which were too heavy for boat operations and unsafe for sledge operations. Then in the period during 2001 a fire occurred which resulted in loss of use of the laboratory at Rothera. It was not possible to restart observations until replacement equipment arrived with the relief of the Rothera Research Station the following December.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Rothera Oceanographic and Biological Time Series (RaTS) Fixed Station

The RaTS fixed station is made up of 3 CTD sampling sites and 2 mooring sites. The main CTD site is located in Marguerite Bay, ~4 km from shore and over a water depth of ~520 m. Marguerite Bay is enclosed by Adelaide Island to the north, Alexander Island to the south and the Antarctic Peninsula to the east (Figure 1 and 2). Waters are strongly influenced by the Antarctic Circumpolar Current. Surface waters during summer become warm through insolation and freshened by ice melt. In winter surface waters are generally colder and more saline and characterised by a thick mixed layer which persists into the summer months and is marked by a subsurface temperature minimum (for fuller details please see Meredith et al., 2004 and references therein). When optimal conditions aren't available the secondary CTD site is occupied. In times when fast ice prevented sampling at both the primary and secondary site, a third site is utilised close to the Rothera Research Station. However, only a water sample is collected during this time as the water is too shallow to allow for a cast to be conducted. The following provides details of the CTD sites sampled:

To compliment the CTD data collected at the RaTS station, fixed moorings were deployed between 2005 - 2007. The moorings consisted of a suite of sensors including ADCPs, CTDs and sediment traps.

Figures Location of Maguerite Bay, to the west of the Antarctic Peninsula (Meredith et al., 2004) and more specifically the location of the RaTS station (Wallace, 2007)

Reference

Meredith, M.P., I.A. Renfew, A. Clark, J.C. King, M.A. Brandon (2004) Impact of the 1997/98 ENSO on upper ocean characteristics in Marguerite Bay, western Antarctic Peninsula. Journal of Geophysical Research Letters, Vol. 109, C09013, doi:10.1029/2003JC001784

Wallace, M.I., 2007. Ocean circulation, properties and variability in Marguerite Bay, west Antarctic Peninsula. PhD Thesis. The Open University, Milton Keynes, UK.

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: RaTS, Rothera

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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