Metadata Report for BODC Series Reference Number 1894067

• 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

RRS James Clark Ross JR20120120 (JR255A) CTD Data Quality Report

Please be aware of the following data quality issues for the below channels noted by the originator. BODC also screened the data and applied flags to any obvious outliers and spikes.

TEMPCC01 - The originator has stated the temperature sensors show a pressure dependent divergence in the order of 0.5*10^-3°C / 3500 dbar. This is small but noticeable; there was no way of correcting this divergence. Notification was sent to BAS that post cruise factory calibration is needed for these sensors, to determine ultimately which of these sensors or both were affected.

CNDCST01 - The originator has stated both conductivity sensors showed an offset when calibrated against bottle samples. Otherwise both seem to be stable. The slight pressure dependence of secondary conductivity sensor is most likely due to the pressure drift of secondary temperature sensor and too small to correct.

POPTDR01 - The originator has stated the data have not been calibrated. BODC have applied flags where values are greater than the maximum parameter limit as this is not to be expected.

AHSFZZ01 - BODC have applied flags where the values are constant or increase with depth. The altimeter only collects good data within 100 m of the seabed and these instances of constant values or increases with depth occur more than 100 m from the seabed.

DOXYSC01 and OXYSZZ01 - BODC have applied flags at the start of the profile for Series 1894239 and 1894240, where sensor seems to have not settled in the surface waters.

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.

RRS James Clark Ross JR20120120 (JR255A) CTD Instrumentation

A Sea-Bird 911 plus CTD system was used on cruise JR20120120 (JR255A). This was mounted on a SBE-32 carousel water sampler holding 24 12-litre Niskin bottles. The CTD was fitted with the following scientific sensors:

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.

SeaBird SBE35 Deep Ocean Standards Thermometer

The SBE 35 is a high precision thermometer that can be used in fixed point cells or at depths up to 6800 m. It is not affected by shock and vibration, allowing it to be used in calibration laboratories and for thermodynamic measurement of hydro turbine efficiency.

The SBE35 can be used with the SBE32 Carousel Water Sampler and with a real-time or autonomous CTD system. In this case, an SBE35 temperature measurement is collected each time a bottle is fired and the value is stored in EEPROM (Electrically Erasable Programmable Read-Only Memory), eliminating the need for reversing thermometers while providing a high accuracy temperature reading.

The SBE35 is standardized in water triple point (0.0100 °C) and gallium melting point (29.7646 °C) cells, following the methodology applied to the Standard-Grade Platinum Resistance Thermometer (SPRT). However, it does not need a resistance bridge, making it more cost-efficient than an SPRT.

Temperature is determined by applying an AC excitation to reference resistances and an ultrastable aged thermistor. Each of the resulting outputs is digitized by a 20-bit A/D converter. The AC excitation and ratiometric comparison uses a common processing channel, which removes measurement errors due to parasitic thermocouples, offset voltages, leakage currents and gain errors.

Specifications

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

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.

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.

Paroscientific Absolute Pressure Transducers Series 3000 and 4000

Paroscientific Series 3000 and 4000 pressure transducers use a Digiquartz pressure sensor to provide high accuracy and precision data. The sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

The 3000 series of transducers includes one model, the 31K-101, whereas the 4000 series includes several models, listed in the table below. All transducers exhibit repeatability of better than ±0.01% full pressure scale, hysteresis of better than ±0.02% full scale and acceleration sensitivity of ±0.008% full scale /g (three axis average). Pressure resolution is better than 0.0001% and accuracy is typically 0.01% over a broad range of temperatures.

Differences between the models lie in their pressure and operating temperature ranges, as detailed 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.

RRS James Clark Ross JR20120120 (JR255A) CTD BODC Processing

Data Processing

Originator data files were submitted in matlab format and included files containing averaged data at 2db, downcast data averaged at 1db and upcast data averaged at 1db.

BODC will only be ingesting the downcast data averaged at 1db into the database. All the original files submitted are available on request.

The files were transferred into BODC's internal NetCDf format and original variables were mapped to the appropiate BODC codes, as follows:

Channels that were not transferred are available on request.

Screening

Screening of data files were then completed using the in-house software EDSERPLO, which allows a visual inspection to take place of the data values and to flag any missing data or obvious spikes in the data.

References

Benson B.B. and Krause D., 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr., 29(3), 620-632.

Fofonoff N.P. and Millard R.C., 1983. Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science No. 44, 53pp.

RRS James Clark Ross JR20120120 (JR255A) CTD Data Originator's Processing

Originator's Sampling

A total of 41 CTDs were deployed at various stations in the Southern Ocean as part of the WOCE SR4 repeat section last surveyed on the ADELIE project (Casts 1-15), a high resolution survey of Powell Basin (Cast 16, 18-28 and 40), a survey of an eddy south of Clarence Island (Casts 31-39) and at glider deployment and recovery sites.

Orignator's Processing

Standard SeaBird Software Version Seasave V 7.21d was used for data collection and conductivity cell thermal mass correction. The recommended standard Seabird correction via a reverse filter to conductivity is applied to both sensors to correct effects of conductivity cell thermal mass in sharp thermoclines. This is likely negligible for all casts of this cruise with a maximum thermocline below 2°C, but applied to adjust theoretically known errors. The SBE-11plus manufacturer recommended values were used: thermal anomaly amplitude, a=0.03, thermal anomaly time constant 1/ß=7.

Standard UEA CTD handling MatLab scripts were used, as on previous cruises. Minor changes to the scripts were made and are described in detail below:

• Ctdcal.m - used to read in the SeaBird data format.
• Offpress.m - corrects the profiles for the deck pressure offset.
• Spike.m - remove high frequency fluctuations in all measurements, resulting from various sources, spanning from organic material being pumped in the conductivity cell to data transmission noise via the sea cable.Conductivity is despiked with a threshold of 0.03, temperature with 0.04. A final salinity despiking is applied with a threshold of 0.009. Oxygen is despiked with a threshold 2, the transmissionmeter with 0.4 and the fluorometer with 0.01. Despiking allows data point to data point variations (within 1/24th of a second, sampled at 24Hz) smaller or equal to the threshold. Larger changes are eliminated by setting them to NaN.
• Interpol.m - used to interpolate across the gaps from spike.m . They are usually in the order of 1-5 data points, equivalent to a loss of up to 1/5th of a second data.
• Makebot.m - used to create MatLab readable code from the bottle data captures.
• newvar_cal.m - is used to apply the conductivity calibration derived from salinometer measurements (see CTD conductivity calibration section 2.5 and Salinometer section 3.1) and compute salinity from corrected conductivity.
• Splitcast.m - The cast is further split into a up and down cast. Since the water sampler has significant water drag, only the downcast is used in the following. Cast 41 will be treated different and is not ideally processed due to large swell during the CTD cast, resulting in mixing around the CTD that was lowered slowly.
• ctd2db.m; ctd1dbup.m; ctd1dbdn.m and ctd05dbdn.m - The cast is finally subsampled onto a vertical 2, 1 and 0.5 dbar grid with respective m-files. This is done by using the median in each property within each depth interval. (0.5 to 1.5 dbar for the 1dbar grid point)

CTD Calibration

Details of calibrations taken place can be found on page 14 of the cruise report.

Project Information

Gliders: Excellent New Tools for Observing the Ocean (GENTOO)

Funding

Funding was provided by NERC through the 11^th round of the Antarctic Funding Initiative (AFI), an annual competition-based award which is supported logistically by the British Antarctic Survey (BAS). The award had a total value of £1,070,531 which was split between different researchers at various international institutions in the form of grants, fellowships and training grant records.

Project dates - 06 September 2010 to 31 March 2015

Background

Research has shown that surface waters surrounding Antarctica play an important role in driving the global oceanic circulation as they are subjected to ideal physical conditions to become denser and sink at specific locations. The mapping of these locations and the identification of the properties of these water cells have been relying on expensive and season-dependent shipborne observations in impractical polar seas. This study aims at revealing the potential of Seagliders, which are autonomous, inexpensive and sustainable underwater vehicles able to carry out certain physical, biological and chemical measurements of the water column all year round. Seagliders were deployed in the Weddell Sea, as the recent collapse of the Larsen Ice Shelf has raised questions on whether dense water may now be spilling off the continental shelf on the eastern side of the Antarctic Peninsula. Changes in location of deep water formation may affect local oceanic currents and consequently the global circulation and the Earth's climate; reliable mapping and description of the Antarctic waters are therefore key to generate accurate climate and circulation models and predictions. Possible changes in the ocean currents also affect the organisms living in the waters near Antarctica. In particular, krill lay eggs around the Antarctic Peninsula and rely on ocean currents to transport them to South Georgia. It is important to determine whether changes in the local circulation may impact krill's ecosystem, as animals such as whales, seals and penguins feed on them and they support a multi-million pound krill fishing industry. In light of the decreasing availability of resources for an increasing human population, the possibility of krill's immunity to temperature and circulation changes may result in a popular food resource for people in the future.

Objectives

The main objectives of the GENTOO project depend on a critical evaluation of the ability to measure current velocity and krill biomass from a glider.

1) To quantify and understand the possible new source of dense water overflow and its variability; to determine the outflow's potential as an early indicator of Antarctic climate change; to assess the impact of changing dense overflows on the locations and strengths of the surface currents and frontal jets; to provide valuable constraints for climate models that describe how changes in ocean circulation feedback on and regulate climate change in polar latitudes.

2) To determine the krill biomass distribution and (temporal and spatial) variability to the east of the Antarctic Peninsula and its likely impact on the circumpolar krill ecosystem; to assess the impact of any variations in the location of the frontal jets (from objective 1) on the krill biomass distribution; to alleviate a severe regional lack of field data on krill, a key species in the Antarctic food web.

Participants

• University of East Anglia, United Kingdom (Lead Research Organisation)
• NOAA - National Oceanic and Atmospheric Administration, United States
• Bjerknes Centre for Climate Research, Norway
• AWI - Alfred Wegener Institute for Polar and Marine Research, Germany
• VIMS - Virginia Institute of Marine Science, United States

• Prof. Karen Heywood, University of East Anglia, Environmental Science (Principal Investigator)
• Dr. Sophie Fielding, NERC British Antarctic Survey, Science Programmes
• Prof. Gwyn Griffiths, National Oceanography Centre, Science and Technology
• Dr. Stuart Dalziel, University of Cambridge, Applied Mathematics and Theoretical Physics
• Dr. Eugene Murphy, NERC British Antarctic Survey, Science Programmes
• Dr. Andrew Thompson, California Institute of Technology, Environmental Science and Engineering.

Methodology

During cruise RRS James Clark Ross 255A three Seagliders were deployed, and a hydrographic survey was undertaken together with nets and underway biological, chemical and physical measurements. The data gathered was analysed to meet the objectives listed above. Please read the 'Instrumentation' section below, and visit the GENTOO website for more information on the methodology and outcomes of the various research studies.

Fieldwork

• RRS James Clark Ross 255A - 20 January 2012 to 03 February 2012. Port of arrival and departure is Stanley, Falkland Islands (Malvinas). Study area - Drake Passage, Weddell Sea, Powell Basin. Principal Scientist - Dr. Karen Heywood, University of East Anglia. This was the glider deployment cruise and the primary data gathering exercise.
• RRS James Clark Ross 255B - 07 February 2012 to 22 March 2012. Port of arrival and departure is Stanley, Falkland Islands (Malvinas). This was the glider recovery cruise; other projects not linked to GENTOO shared the voyage.

Instrumentation

• Seagliders - three in total, each equipped with a Seabird CT sail (i.e. free-flushed temperature and conductivity sensors), Aandera oxygen optode and a WETLabs ECO Triplet. (Biddle et al. 2015)
• SeaBird (SBE) CTD-11plus rosette equipped with 24 12-litre Niskin bottles. Sensors installed are SBE 43 Oxygen sensor, LI-COR Biospherical PAR Sensor, Chelsea Aqua 3 Fluorometer, WET Labs C-Star Transmissometer, and Altimeter sensor.
• 300 kHz WorkHorse (WH) Lowered Acoustic Doppler Current Profiler (LADCP)
• 75 kHz RD Instruments Ocean SUrveyor (OS75) Vessel-Mounted Acoustic Doppler Current Profiler (ADCP)
• Surface drifters: 20 Clearsat-15 Minidrogue drifters with a GPS navigation option and 20 Clearsat-15 SVP Minidrigue drifters with Argos data telemetry, both purchased from Clearwater Instrumentation, Inc.
• Three AOEX-SBE Argo floats profilers produced by Webb Research Corporation USA.
• RMT8 Nets Macrozooplankton
• Guildline Autosal salinometer
• Winkler O₂ titrator
• Simrad EK60 Echo Sounder
• Underway - navigation, surface and meteorology.

Contacts

References

Biddle, L.C., Kaiser J., Heywood K.J., Thompson A.F., and Jenkins A., 2015. Ocean glider observations of iceberg-enhanced biological production in the northwestern Weddell Sea, Geophys. Res. Lett. (42), 459-465.

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: