Metadata Report for BODC Series Reference Number 1002840

• 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

Chlorophyll profiles show numerous instances where there are negative values, especially where the instrument output should be 0. This suggests the manufacturer's calibration is underestimating concentrations, data should be used with caution.

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.

Instrument Description

CTD Unit and Auxiliary Sensors

SeaBird SBE9 plus CTD (serial 704), with dual temperature, conductivity sensors and a Tritech 500 kHz altimeter mounted on a SeaBird 24 bottle rosette frame, together with a SBE32 24 position pylon and 22 x 10 litre General Oceanics Niskin bottles. The following additional sensors were mounted:

CTD data were transmitted up a 6 mm seacable to a SBE11plusV2 deck unit, at a rate of 24 Hz, and data were logged simultaneously on 2 PC's using SeaBird data acquisition software "Seasave". The LADCP was powered by a separate battery pack, and data were logged internally and downloaded after each CTD cast. Note that physical mounting of the upward looking LADCP transducer set requires removal of 2 Niskin bottles, thus only 22 Niskins were fitted for the cruises.

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.

WETLabs ECO-FL Fluorometer

The Environmental Characterization Optics series of single channel fluorometers are designed to measure concentrations of natural and synthetic substances in water, and are therefore useful for biological monitoring and dye trace studies. Selected excitation and emission filters allow detection of the following substances: chlorophyll-a, coloured dissolved organic matter (CDOM), uranine (fluorescein), rhodamine, phycoerythrin and phycocyanin.

The ECO-FL can operate continuously or periodically and has two different types of connectors to output the data (analogue and RS-232 serial output). The potted optics block results in long term stability of the instrument and the optional anti-biofouling technology delivers truly long term field measurements.

In addition to the standard model, five variants are available, and the differences between these and the basic ECO-FL are listed below:

• FL(RT): similar to the FL but operates continuously when power is supplied
• FL(RT)D: similar model to the (RT) but has a depth rating of 6000 m
• FLB: includes internal batteries for autonomous operation and periodic sampling
• FLS: similar to FLB but has an integrated anti-fouling bio-wiper
• FLSB: similar to the FLS, but includes internal batteries for autonomous operation

Specifications

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

Biospherical Instruments Log Quantum Cosine Irradiance Sensor QCP-2300 & QCP-2350

The QCP-2300 is a submersible cosine-collector radiometer designed to measure irradiance over Photosynthetically Active Radiation (PAR) wavelengths. It features a constant (better than ±10%) quantum response from 400 to 700 nm with the response being sharply attenuated above 700 nm and below 400 nm.

The sensor is a blue-enhanced high stability silicon photovoltaic detector with dielectric and absorbing glass filter assembly. The output is a DC voltage typically between 0 and 5 VDC that is proportional to the log of the incident irradiance.

The QCP-2300 is specifically designed for integration with 12-bit CTD systems and dataloggers requiring a limited-range of signal input.

Specifications

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

BODC Processing

Files were provided to BODC in WOCE exchange format (micro moles per kilogram) and in volumetric units (micro moles per litre). Only the 73 CTD data files in volumetric units were transferred to BODC's NetCDF format (QXF) using BODC generated Matlab code. The transfer automatically converted the conductivity channels from mS/cm to S/m.

The following table shows how the variables within the originator's data files were mapped to the BODC parameter codes:

The reformatted data were screened using in-house visualisation software called EDSERPLO. Suspect data points were marked by adding an appropriate quality control flag.

Originator's Data Processing

Sampling Strategy

Oceanographic measurements were collected aboard Aurora Australis cruise au0806 (voyage 6 2007/2008, 22nd March 2008 to 17th April 2008). Cruise au0806 completed the CASO oceanographic program, with a full occupation of the SR3 transect between Antarctica and Tasmania, and included GEOTRACES program trace metal work. A total of 73 vertical CTD profile were taken.

CTD data processing

The following information has been taken from Rosenberg and Rintoul 2010

The CTD deployment method was as follows:

* CTD initially deployed down to ~10 to 20 m
* after confirmation of pump operation, CTD returned up to just below the surface (depth dependent on sea state)
* after returning to just below the surface, downcast proper commenced

Pre cruise temperature, conductivity and pressure calibrations were performed by the CSIRO Division of Marine and Atmospheric Research calibration facility (April to May 2007). Manufacturer supplied calibrations were used for the dissolved oxygen, fluorometer and altimeter. PAR sensor data were uncalibrated (raw voltage data only). Final conductivity and dissolved oxygen calibrations derived from in situ Niskin bottle samples can be found in the originators report Rosenberg and Rintoul 2010

Preliminary CTD data processing was performed at sea, to confirm correct functioning of instrumentation. Final processing of the data was done in Hobart. The first processing step is application of a suite of the SeaBird "Seasoft" processing programs to the raw data, in order to:

* convert raw data signals to engineering units
* remove the surface pressure offset for each station
* realign the oxygen sensor with respect to time (note that conductivity sensor alignment is done by the deck unit at the time of data logging)
* remove conductivity cell thermal mass effects
* apply a low pass filter to the pressure data
* flag pressure reversals
* search for bad data (e.g. due to sensor fouling)

For au0806, an additional processing step was performed early on, running all data through the SeaBird data despiking program "wildedit". Further processing and data calibration were done in a UNIX environment, using a suite of fortran programs. Processing steps here include:

* forming upcast burst CTD data for calibration against bottle data, where each upcast burst is the average of 10 seconds of data prior to each Niskin bottle firing
* forming pressure monotonically increasing data, and from there calculating 2 dbar averaged downcast CTD data
* calculating calibrated 2 dbar averaged salinity from the 2 dbar pressure, temperature and conductivity values
* deriving CTD dissolved oxygen calibration coefficients by comparing bottle sample dissolved oxygen values (collected on the upcast) with CTD dissolved oxygen values from the equivalent 2 dbar downcast pressures
* extracting the appropriate fluorescence data to assign to each 2 dbar bin

For calibration of the CTD oxygen data, whole profile fits were used for shallower stations, while split profile fits were used for deeper stations. Final station header information, including station positions at the start, bottom and end of each CTD cast, were obtained from underway data for the cruise.

Note the following for the station header information:

* All times are UTC.
* "Start of cast" information is at the commencement of the downcast proper, as described above.
* "End of cast" information is when the CTD leaves the water at the end of the cast, as indicated by a drop in salinity values.
* All bottom depth values are corrected for local sound speed, where sound speed values are calculated from the CTD data at each station.
* "Bottom of cast" depths are calculated from CTD maximum pressure and altimeter values at the bottom of the casts.
Lastly, data were converted to MATLAB format, and final data quality checking was done within MATLAB.

CTD Calibration

Data from the primary CTD sensor pair (temperature and conductivity) were used. For a more detailed description of calibration and CTD processing please see Rosenberg and Rintoul 2010

Conductivity/salinity

Please refer to Rosenberg and Rintoul 2010 for the conductivity calibration and equivalent salinity results. International standard seawater batch numbers used for salinometer standardisation were as follows:

station 1-8, 11-73 P147 (6th June 2006)
station 9-10 P148 (10th June 2006)
The salinometer (Guildline Autosal serial 62548) appeared stable throughout the cruise. Overall, CTD salinity for the cruise can be considered accurate to better than 0.0015 (PSS78).

Temperature

The primary and secondary CTD temperature data (tp and ts respectively) were compared for the cruise and a very small pressure dependency (tp-ts) was evident for the full ocean depth range, of the order 0.0005^oC. However tp-ts starts from an average value of ~-0.0005^oC at the surface, decreasing to ~-0.001^oC at the bottom, indicating an initial calibration offset between the two temperature sensors. The magnitude of the tp-ts pressure dependency is within the assumed temperature accuracy of 0.001^oC. However without some temperature standard for comparison, it is unknown which of the temperature sensors provides more accurate data overall for cruises au0806. Data spikes in the secondary temperature sensor were common at temperatures below 0^oC, so primary sensor data were used.

Pressure

Surface pressure offsets for each cast were obtained from inspection of the data before the package entered the water. Data transmission errors initially caused some pressure spiking. The problem was fixed after retermination of the CTD wire (after station 3).

Dissolved oxygen

CTD oxygen data were calibrated using split profile fits. Plots and calibration coefficients can be found in Rosenberg and Rintoul 2010 Overall the calibrated CTD oxygen agrees with the bottle data to well within 1% of full scale (where full scale is ~350 umol/l above 1500 dbar, and ~260 umol/l below 1500 dbar).

Bottle overlaps between the shallow and deep fits were varied slightly for some stations, while merging of the fits was changed to 2500 dbar for station 60, 2000 dbar for station 64, and 1000 dbar for station 65. For stations 15 and 55, whole profile fits were required to improve the calibration for the top part of the profile. For stations 47 and 64, CTD oxygen accuracy is reduced for most of the top half of the profile (Table 9), due to sparse bottle samples.

Fluorescence, PAR, altimeter

All fluorescence data for the cruise have been calibrated using the manufacturers calibration coefficient. PAR sensor data are uncalibrated, and supplied as raw voltages.

In these files, fluorescence data are not in fact averages: they are the minimum value within each 2 dbar bin, providing a profile "envelope" which minimizes the spikiness of the data.

For the Tritech 500 kHz altimeter used on the cruises, on some stations a false bottom reading was obtained before coming within the nominal altimeter range of 50 m. This false bottom could be due to detection of the echo from the previous altimeter ping, or alternatively a combination of a good echo return from the bottom and a slightly better range in cold water. As a result of this behaviour, the real bottom was missed for a few stations. Note that similar behaviour for Tritech 500 kHz altimeters has been observed elsewhere (RV Tangaroa).

References

Rosenberg and Rintoul 2010. Aurora Australis Marine Science Cruises AU0803 and AU0806. Oceanographic Field Measurements and Analysis

Project Information

GEOTRACES

Introduction

GEOTRACES is an international programme sponsored by SCOR which aims to improve our understanding of biogeochemical cycles and large-scale distribution of trace elements and their isotopes (TEIs) in the marine environment. The global field programme started in 2009 and will run for at least a decade. Before the official launch of GEOTRACES, fieldwork was carried out as part of the International Polar Year (IPY)(2007-2009) where 14 cruises were connected to GEOTRACES.

GEOTRACES is expected to become the largest programme to focus on the chemistry of the oceans and will improve our understanding of past, present and future distributions of TEIs and their relationships to important global processes.

This initiative was prompted by the increasing recognition that TEIs are playing a crucial role as regulators and recorders of important biogeochemical and physical processes that control the structure and productivity of marine ecosystems, the dispersion of contaminants in the marine environment, the level of greenhouse gases in the atmosphere, and global climate.

Scientific Objectives

GEOTRACES mission is: To identify processes and quantify fluxes that control the distribution of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions.

Three overriding goals support the GEOTRACES mission

• Determine ocean distributions of selected TEIs at all major ocean basins
• Evaluate the sources, sinks, and internal cycling of these TEIs and thereby characterize more completely their global biogeochemical cycles
• Provide a baseline distribution in the Polar Regions as reference for assessing past and future changes.

These goals will be pursued through complementary research strategies, including observations, experiments and modelling.

Fieldwork

The central component of GEOTRACES fieldwork will be a series of cruises spanning all Ocean basins see map below.

Three types of cruise are required to meet the goals set out by GEOTRACES. These are

• Section cruises - These will measure all the key parameters (see below) over the full depth of the water column. The sections were discussed and approved by the International GEOTRACES Scientific Steering Committee at the basin workshops.
• Process Studies - These will investigate a particular process relevant to the cycling of trace metal and isotopes. They must follow the "Criteria for Establishing GEOTRACES Process Studies" and be approved by the International GEOTRACES Scientific Steering Committee.
• Cruises collecting GEOTRACES compliant data - These will collect some trace element or isotope data. They must follow the GEOTRACES Intercalibration and Data Management protocols

IPY-GEOTRACES

The IPY-GEOTRACES programme comprised of 14 research cruises on ships from 7 nations; Australia, Canada, France, Germany, New Zealand, Japan and Russia. The cruises will not be classified in the same way as the full GEOTRACES programme since the intercalibration protocols and data management protocols had not been established before the start of the IPY. But IPY-GEOTRACES data will still be quality controlled by GDAC and in the majority of cases verified versus Intercalibration standards or protocols.

Key parameters

The key parameters as set out by the GEOTRACES science plan are as follows: Fe, Al, Zn, Mn, Cd, Cu; 15N, 13C; 230Th, 231Pa; Pb isotopes, Nd isotopes; stored sample, particles, aerosols.

Weblink:

http://www.bodc.ac.uk/geotraces/
http://www.geotraces.org/

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: