Metadata Report for BODC Series Reference Number 704635

• 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 supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

RRS James Clark Ross JR20011119 (JR67, JR69) CTD Instrumentation

A Sea-Bird 911 plus CTD system was used on cruise JR20011119. The CTD was fitted with the following scientific sensors:

Some calibration dates are unavailable.

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 CTD data were supplied to BODC as Matlab files and converted to the BODC internal format.

During transfer the originator's variables were mapped to unique BODC parameter codes. The following table shows the parameter mapping.

Following transfer the data were screened using BODC in-house visualisation software. Suspect data values were assigned the appropriate BODC data quality flag. Missing data values, where present, were changed to the missing data value and assigned a BODC data quality flag.

RRS James Clark Ross cruise JR20011119 (JR67, JR69) Originator's CTD data processing

The following information contains extracts from the JR67 cruise report.

Sampling strategy

The RRS James Clark Ross cruise JR20011119 (JR67, JR69) aimed to carry out a 7th repeat hydrography section of the Drake Passage, first established during the World Ocean Circulation Experiment (WOCE).

Thirty CTD/LADCP stations were carried out across the 753 km section from Burdwood Bank to Elephant Island, plus one test station, one station in Drake Passage to provide sound speed information for concurrent geophysical activities, and one station at the Rothera Time Series (RaTS) site, just off Biscoe Wharf at Rothera. Maximum station spacing on the section was 33 km, with stations closer together on the continental shelves.

Data Processing

Initial data processing was performed using the SeaBird processing software SBE SEASAVE_Win32 Version 5.22. The following steps were performed:

• Data conversion - converts raw data to physical units.
• Cell thermal mass - takes the .cnv files output from the data conversion and makes corrections for the thermal mass of the cell, in an attempt to minimize salinity spiking in steep vertical gradients.
• Bottle summary - generates an ASCII summary .bl file of the bottle firing data from the cast .ros file.

The entire Mstar software suite is written in Matlab and uses a NetCDF file format to store all the data. The 5 CTD files store all the data from the CTD sensors. These arr: raw, 24Hz, 1Hz, psal and 2db. The Mstar software program averages and interpolates the raw data until it has 2db resolution.

BODC will transfer the 2db resolution CTD data.

Field Calibrations

After the section had been finished it was discovered that out of date pressure calibration values had been used. The correction to the original pressure calibration is applied using a slope and an offset. The effect of the incorrect values was removed from the pressure and the new calibration applied in the following way. slopeold = 0.99999 offsetold = -0.494200 slopenew = 0.99992 offsetnew = -0.8815 to give: Pnew= Pold*0.99993 − 0.387273

Salinity derived from the primary conductivity-temperature sensors were calibrated against salinity derived from bottle samples at the same depths. Samples were used from depths of 2000 metres or more. Ignoring outliers, considering only data below 2500db, the following calibrations were derived: C1new = C1old – 0.00175 + 0.0000835*station number C2new = C2old – 0.00188

References

Bacon, S.. (2002). 'Drake Passage repeat hydrography: WOCE Southern Repeat Section 1b – Burdwood Bank to Elephant Island'. Cruise Report No. 38 National Oceanography Centre, Southampton.

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.

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: