Metadata Report for BODC Series Reference Number 1227024

• 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

Transmissometer Data Quality Report

The following data quality issues were found during the screening process:

For all ten casts the transmissometer produced values where the majority were outside of the expected range (0-100%). During transfer M flags were applied to all values exceeding 100%. No other flags were applied as no anomalous data were identified.

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

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 unit and attached sensors

A SEA-BIRD electronics 911+ system was used, serial number 0707. The attached sensors are shown in the table below:

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.

Chelsea Technologies Group Aquatracka MKIII fluorometer

The Chelsea Technologies Group Aquatracka MKIII is a logarithmic response fluorometer. Filters are available to enable the instrument to measure chlorophyll, rhodamine, fluorescein and turbidity.

It uses a pulsed (5.5 Hz) xenon light source discharging along two signal paths to eliminate variations in the flashlamp intensity. The reference path measures the intensity of the light source whilst the signal path measures the intensity of the light emitted from the specimen under test. The reference signal and the emitted light signals are then applied to a ratiometric circuit. In this circuit, the ratio of returned signal to reference signal is computed and scaled logarithmically to achieve a wide dynamic range. The logarithmic conversion accuracy is maintained at better than one percent of the reading over the full output range of the instrument.

Two variants of the instrument are available, both manufactured in titanium, capable of operating in depths from shallow water down to 2000 m and 6000 m respectively. The optical characteristics of the instrument in its different detection modes are visible below:

* The wavelengths for the turbidity filters are customer selectable but must be in the range 400 to 700 nm. The same wavelength is used in the excitation path and the emission path.

The instrument measures chlorophyll a, rhodamine and fluorescein with a concentration range of 0.01 µg l^-1 to 100 µg l^-1. The concentration range for turbidity is 0.01 to 100 FTU (other wavelengths are available on request).

The instrument accuracy is ± 0.02 µg l^-1 (or ± 3% of the reading, whichever is greater) for chlorophyll a, rhodamine and fluorescein. The accuracy for turbidity, over a 0 - 10 FTU range, is ± 0.02 FTU (or ± 3% of the reading, whichever is greater).

Further details are available from the Aquatracka MKIII specification sheet.

WETLabs C-Star transmissometer

This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.

Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.

This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.

Specifications

Further details are available in the manufacturer's specification sheet or user guide.

BODC Processing

Data Processing

The data files were processed and calibrated by the originator at the British Antarctic Survey and were sent to BODC in matlab form as 10 individual .mat files.

Reformatting

The parameters included in the originator's files were: lat, lon, gtime (yyyy:mm:dd hh:mm:ss), botdepth (m), pres (dbar), alt (m), flag, fluor (mg l^-1), oxygen (ml l^-1), trans (%), cond1 (mS cm^-1), cond2 (mS cm^-1), sal1 (psu), sal2 (psu), salin (psu), temp1 (°C), temp2 (°C), potemp (°C), potemp1 (°C), potemp2 (°C), sig0 (kg m^-3), sig2 (kg m^-3), sig4 (kg m^-3).

The parameters from the originator's files were reformatted to internal QXF format using BODC standard procedures. Certain parameters were not transferred as they: are derived parameters and BODC's standard procedures mean that these channels are re-derived during transfer, contain metadata or are not environmental variables.

For those parameters which had primary and secondary sensors, data from both channels were transferred but after screening, given that both channels exhibited a similar quality, the secondary channels were dropped. All secondary channels and PAR data (which is only available in raw files) are available upon request.

The following table shows the final variables and how they were mapped to the appropriate BODC parameter codes:

Screening

During the transfer flags were added to null data and data outside of the expected range. The reformatted data were visualised using in house software Edserplo. Any suspect data were marked by adding a quality control flag (M).

Originator's Data Processing

Sampling Strategy

10 CTD casts were made between Stanley, Falkland Islands and Punta Arenas, Chile during the JR20110319 (JR252, JR254C) cruise which took place from 19 March 2011 to 06 April 2011. The CTDs were deployed at mooring sites in the Orkney Passage. Four bottles were fired on each cast, near the bottom, at 2000m, at the salinity maximum and near the surface.

Data Processing

The CTD casts were processed using a set of matlab scripts written by Karen Heywood (UEA) and Mike Meredith, and then modified by Martin Price and Povl Abrahamsen. The files were sent in .mat format which are Matlab data files containing the CTD data in 2-dbar pressure bins.

Field Calibrations

For the temperature data, points were discarded which gave a raw reading of above 50, or the difference between both sensors and the SBE35 deep ocean standards thermometer is above 0.005°C. From this, 19 points were used to derive the offsets with a standard deviation of 0.0011°C for the primary and 0.0012°C for the secondary sensor.

For the conductivity data, calibrations were based on the analysis of salinity samples using the onboard salinometer (Guideline Autosal 8400B, s/n 68959). The instrument was standardized using IAPSO standard seawater batch P151. Points were discarded which had standard deviations of 0.0005 mS/cm for conductivity or 0.001°C for temperature. From this, 31 points were used to derive the offsets with a standard deviation of 0.0024 mS/cm or 0.0013 PSU for both sensors.

The pressure data has an individual offset per cast based on the deck pressure from before and after the casts. There are no calibrations for the other sensors used in the CTD package. Data from these sensors have not been checked or modified on the cruise and no oxygen titrations were performed, therefore the values should be considered uncalibrated.

Project Information

BAS Long Term Monitoring and Survey

Introduction

The Long Term Monitoring and Survey project (LTMS) has been running since the British Antarctic Survey (BAS) was created. This project is one of the BAS core projects, with several groups of scientists collecting various types of data e.g biological, geological, atmospheric, among others.

Data collection is achievable through a wide scope of instruments and platforms, e.g. the Antarctic research stations, autonomous instrument platforms deployed on or from BAS research ships, BAS aircrafts, satellite remote sensing and others.

Scientific Objectives

This project was implemented in order to measure change and variability in the Earth system. Its long term duration allows for the monitoring of processes that could be missed in shorter term studies and experiments. The data collected is also used to check and improve the reliability of models used to stimulate and predict the behavior of the Earth system.

The main objectives are:

• Topographic survey
• Geosciences survey
• Biological survey and monitoring
• Atmospheric and oceanographic monitoring

Data Availability

The data sets obtained through this project are available to the academic community.

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: