Metadata Report for BODC Series Reference Number 971140

• 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 Quality Report

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

Instrumentation

During the BAS core cruise JR20061024 (JR161), a full size SBE 24 carousel water sampler, holding 12 bottles, connected to an SBE 9 plus CTD and a SBE 11 plus deck unitwas used to collect vertical profiles of the water column. The deck unit provides power, real time data acquisition and control. The underwater SBE 9 plus unit featured dual temperature (SBE 3 plus) and conductivity (SBE 4) sensors, and a Paroscientific pressure sensor. A temperature-conductivity (TC) duct and a pump-controlled flow system ensured that the flow through the TC duct is constant to minimize salinity spiking.

In addition, a Tritech PA200 Digital Precision Altimeter, a Chelsea Aquatracker III fluorometer, a SBE 43 oxygen sensor, a Biospherical QCD905L photosynthetically active radiation (PAR) sensor and a Wet-Labs C-Star Transmissometer (6000 m; red wavelength; 25cm pathlength) were attached to the carousel.

The CTD data were logged via the deck unit to a 1.4GHz P4 PC, running Seasave Win32 version 5.7b (Sea-Bird Electronics Inc.). The data rate of recorded data for the CTD was 24 Hz.

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.

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

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

Biospherical Instruments Log Quantum Cosine Irradiance Sensor QCD-905L

The QCD-905L is a submersible radiometer designed to measure irradiance over Photosynthetically Active Radiation (PAR) wavelengths (400-700 nm). It features a cosine directional response when fully immersed in water.

The sensor is a blue-enhanced high stability silicon photovoltaic detector with dielectric and absorbing glass filter assembly, and produces a logarithmic output. Normal output range is -1 to 6 volts with 1 volt per decade. Typically, the instrument outputs 5 volts for full sunlight and has a minimum output of 0.001% full sunlight, where typical noon solar irradiance is 1.5 to 2 x 10¹⁷ quanta cm^-2 s^-1. The instrument can be calibrated with constants for µE cm^-2 s^-1 or quanta cm^-2 s^-1.

The QCD-905L can be coupled to a fixed range data acquisition system like a CTD (Conductivity-Temperature-Depth) profiler or current meter. It has an aluminium and PET housing, and a depth rating of 7000 m.

Specifications

Further details can be found in the manufacturer's manual.

Tritech Digital Precision Altimeter PA200

This altimeter is a sonar ranging device that gives the height above the sea bed when mounted vertically. When mounted in any other attitude the sensor provides a subsea distance. It can be configured to operate on its own or under control from an external unit and can be supplied with simultaneous analogue and digital outputs, allowing them to interface to PC devices, data loggers, telemetry systems and multiplexers.

These instruments can be supplied with different housings, stainless steel, plastic and aluminum, which will limit the depth rating. There are three models available: the PA200-20S, PA200-10L and the PA500-6S, whose transducer options differ slightly.

Specifications

Common specifications are presented below

Further details can be found in the manufacturer's 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

The data arrived at BODC in NetCDF (m*) format representing the CTD data collected during BAS core cruise JR20071230 (JR177). These were reformatted to the internal QXF format using BODC established procedures. The following table shows how the variables within the originator's data files were mapped to the 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.

The originator sent duplicate data for Temperature, Salinity and Conductivity. According to BODC procedures, and due to the fact that both primary and secondary channels exhibit the same quality, only the primary channels were kept in the final file. The data from the secondary channels is available upon request.

Originator's Data Processing

Sampling Strategy

A total of 58 CTD casts were completed during cruise JR20071230 (JR177) which included one test station, eight biological stations, thirty two physics station plus additional CTD casts as mooring recovery/deployment sites. At each of the biological stations, at least three CTDs were carried out: one full depth CTD and two water sample CTDs to 400m and 2000m (or the seabed, if shallower than 2000m). Two of the biological stations also involved mooring recovery and redeployment, and CTD casts to 400m were carried out at the mooring site. On all physics casts samples were collected for salinity analysis which would be subsequently applied to calibrate the salinity channels from the CTD package.

The general deployment procedure was to start data logging, deploy the CTD, then stop the instrument at 10m wireout, where the CTD package was left for at least two minutes to allow the seawater-activated pumps to switch on and the sensors to equilibrate with ambient conditions.The pumps typically do not operate until 30-60 seconds after the CTD has been in the water. After a two minute soak, the package was raised to just below the surface and then continuously lowered to near bottom, with the Niskin bottles being closed during the upcast. The final CTD product was formed from the calibrated downcast data averaged to 2 db intervals.

Data Acquisition and CTD data processing

The CTD data were output to individual PStar files using the Seasave Win 32 version 5.28e module. The CTD data were then subsequently converted from binary to ascii and calibrated by running the Sea-Bird Electronics Inc. Data Processing software version 5.37b Data Conversion module.

The following routine from Sea-Bird Electronics Inc. Data Processing software version 5.37b was applied:

• Cell thermal mass module. Used to remove the conductivity cell thermal mass effects from the measured conductivity. This takes the output from the data conversion program and re-derives the pressure and conductivity to take into account the temperature of the pressure sensor and the action of pressure on the conductivity cell.

Further processing of CTD data was carried out in Matlab using existing programs, predominantly written by Mike Meredith and Karen Heywood, with modifications by others. These scripts included functions to apply a pressure offset based on CTD deck pressure, remove large spikes in all channels, interpolate missing data, apply derived offsets to the CTD conductivities and calculate salinity, potential temperature and potential densities. For full details of all calculations applied to this data set please see the JR20071230 (JR177) cruise report.

Project Information

DISCOVERY 2010

DISCOVERY 2010 will investigate and describe the response of an ocean ecosystem to climate variability, climate change and commercial exploitation. The programme builds on past studies by BAS on the detailed nature of the South Georgia marine ecosystem and its links with the large-scale physical and biological behaviour of the Southern Ocean.

The aim is to identify, quantify and model key interactions and processes on scales that range from microscopic life forms to higher predators (penguins, albatrosses, seals and whales), and from the local to the circumpolar.

Objectives

Assess the links between the status of local marine food webs and variability and change in the Southern Ocean. Develop a linked set of ecosystem models applying relevant marine physics and biology over scales from the local to that of the entire Southern Ocean.

Relevance to Global Science

Ocean ecosystems play a crucial role in maintaining biodiversity, in depositing carbon into the deep ocean, and as a source of protein for humans. However, fishing and climate change are having significant and often detrimental effects. To predict the future state of ocean ecosystems we must develop computer models capable of simulating biological and physical processes on a range of scales from the local to an entire ocean. Developing such predictive models is crucial to the sustainable management of world fisheries and requires integrated analyses of the way whole ecosystems work. DISCOVERY 2010 aims to take this work forward and at the same time help manage the South Georgia and South Sandwich Islands maritime zone. We will do this through providing information on the state of the ecosystem to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), the international body that manages sustainable fishing in the Southern Ocean.

Delivering the Results

DISCOVERY 2010 will undertake an integrated programme of shipboard and land-based field studies of the marine food web, combined with modelling. We will pay particular attention to critical phases in the life cycles of key species, and to examining interactive effects in food webs. Interacting biological and physical processes will be modelled across a range of spatial scales to significantly improve our representation of the ocean ecosystem, upon which sustainable management and the prediction of future climate change can be based. DISCOVERY 2010 will link to BIOFLAME, ACES, and COMPLEXITY, two international programmes, and to a collaborative programme with the University of East Anglia on the role of the Southern Ocean in the global carbon cycle.

Component Projects

• DISCOVERY-OEM: Ocean Ecosystems and Management
• DISCOVERY-FOOD-WEBS: Scotia Sea FOOD-WEBS
• DISCOVERY-FLEXICON: FLEXIbility and CONstraints in life histories
• DISCOVERY-CEMI: Circumpolar Ecosystems; Modelling and Integration

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: