Metadata Report for BODC Series Reference Number 2205585

• 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

CTD data from Cruise JC238 Data Quality Report

This is a data quality report for the 44 CTD casts performed between Thursday 14th July 2022 to Wednesday 27th July 2022 on the James Cook cruise JC238. Casts are referred to as JC238_CTD_XXX_2DB throughout BODC tables & documents.

No major issues were experienced with the stainless steel CTD suite during the cruise, expect on the third cast (JC238_CTD_003_2DB) the transmissometer failed due to its light sensor and was subsequently replaced for the following casts as noted in the instrument description document.

Data Access Policy

Open Data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

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.

JC238 CTD Instrument Description

CTD Unit and Auxillary Sensors

A Sea-Bird 911plus CTD system was used on cruise JC238. This was mounted on a 24-way stainless steel rosette frame, equipped with 12 10-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.

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.

Biospherical Instruments QCP-2350-HP [underwater] PAR sensor

A cosine-corrected PAR quantum irradiance profiling sensor. For use in high-pressure underwater applications with 24 bit ADC systems. Measures light available for photosynthesis on a flat surface. Operation is by a single channel compressed analog output voltage that is proportional to the log of incident PAR (400-700 nm) irradiance. A variant of the QCP-2350 model, it uses a pressure-tolerant BH-4-MP connector. The sensor is designed for operation in waters to depths of up to 10,000 m.

For more information, please see this document: https://www.bodc.ac.uk/data/documents/nodb/pdf/Biospherical_QCP2300_QCP2350_Apr2014.pdf

WETLabs Single-angle Backscattering Meter ECO BB

An optical scattering sensor that measures scattering at 117°. This angle was determined as a minimum convergence point for variations in the volume scattering function induced by suspended materials and water. The measured signal is less determined by the type and size of the materials in the water and is more directly correlated to their concentration.

Several versions are available, with minor differences in their specifications:

• ECO BB(RT)provides analog or RS-232 serial output with 4000 count range
• ECO BB(RT)D adds the possibility of being deployed in depths up to 6000 m while keeping the capabilities of ECO BB(RT)
• ECO BB provides the capabilities of ECO BB(RT) with periodic sampling
• ECO BBB is similar to ECO BB but with internal batteries for autonomous operation
• ECO BBS is similar to ECO BB but with an integrated anti-fouling bio-wiper
• ECO BBSB has the capabilities of ECO BBS but with internal batteries for autonomous operation

Specifications

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

Valeport VA500 altimeter

A titanium-housed acoustic altimeter used for underwater positioning to determine distance to or height above the seabed. Can be mounted used on ROVs, AUVs and other such platforms for various underwater construction and hydrographic applications. The VA500 features a 500kHz broadband transducer offering a range of 0.1m to 100m, a resolution of 1mm and a beam angle +/- 3 degrees. It features RS232 and RS485 digital output as standard, and is supplied with free DataLog X2 software for instrument setup and data display. An optional Valeport miniIPS pressure sensor can be added. The pressure sensor is a temperature compensated piezo-resistive sensor with various ranges available, an accuracy +/- 0.01 percent FS, and a resolution of 0.001 percent FS. The VA500 is depth-rated to 6000m.

For more information, please see this document: https://www.bodc.ac.uk/data/documents/nodb/pdf/Valeport-VA500-Altimeter-Datasheet.pdf

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.

Originator processing of CTD data from Cruise JC238

Sampling Strategy

A total of 44 CTD casts were performed between Thursday 14th July 2022 to Wednesday 27th July 2022 on the James Cook cruise JC238. The CTD casts provided start-point calibrations for instruments to be deployed and end-point calibrations for recovered instruments.

Data Acquisition and Initial Processing

Following the same processing steps of a previous cruise (DY146) the raw CTD data were transferred from the Sea-Bird deck unit to a LINUX machine via Sea-Bird software. The binary files were converted using Sea-Bird processing software (SBE Data Processing). The ASCII files were converted to MSTAR format and MEXEC programs run to process the data which included reducing the frequency of the data from 24Hz to 1Hz, calibrating the data, and averaging the downcast to a 2db pressure grid. Calibrations were produced for the CTD conductivity sensors by merging the salinity sample data with the CTD data. Details of the MEXEC programs used and further details of the processing performed can be found in Evans (2022).

Calibrations

Conductivity

Independent conductivity samples, obtained from the bottles on the CTD frame and measured with the salinometer, were used to calibrate the CTD data. A pressure dependence was found for each sensor and determined with a by-eye fit to the conductivity residuals. Calibration factor:

cond1_cal = cond1(1+(5.5x10^-5 stn + interp1([-10 2300 3100],[-1 -1 4]x10^-4,press))/35)

cond2_cal = cond2(1+(5x10^-5 stn + interp1([-10 1300 3100],[1.5 -0.2 -0.3]x10^-3,press))/35)

Oxygen

A hysteresis correction was applied in the SBE processing, using matching of down- and upcasts on neutral density surfaces to reduce the observed differences. Once an improvement was established all casts were therefore reprocessed using the modified coefficients. The data were converted from µmol/l to µmol/kg using density from oxygen draw temperature and CTD salinity. Scale factors:

Oxygen1 = 1.025+1.2x10^-4(stn)+interp1([-10 400 3100],[-0.9 -0.25 2.7]x10^-2,press)

Oxygen2 = interp1([-10 600 3100],[1.04 1.04 1.06],press)+interp1([1 32 36 40 44],[-2 0 2 -2 1],stn)

Temperature

SBE35 sensors were mounted on the side of the CTD frame for all casts, data from which were used to compare to bottle stop data and check for any drift. Initial readings in shallow water showed a substantial scatter, so a piecewise linear pressure-dependent offset was applied to each sensor. For temp1 the offset was varying from 7x10^-4°C at the surface to 9x10^-4°C at 1000dbar and -17x10^-4°C at a depth of 3100m. Temp2 was offset 1.7x10^-4°C at the surface to 1.6x10^-4°C at 1300dbar and 0.4x10^-4°C at depth, with a trend using CTD cast number as proxy amounting to -8.8x10^-4°C over the 44 casts.

Backscatter, Fluorometer, Transmissometer

These data had no extra processing on the cruise beyond applying the manufacturer's calibrations in the SBE processing. The WET Labs C-Star Transmissometer (CST-1718TR) failed on Cast three and was replaced with CST-2150DR for the subsequent casts.

JC238 Cruise report

Further information can be found in the JC238 Cruise report.

References

Evans, D. Gwyn (2022) RRS Discovery Research Expedition DY146, 4 February 2022 - 9 March 2022. RAPID research expedition report for DY146. Southampton, UK: National Oceanography Centre, Southampton, 158 pp. (National Oceanography Centre Research Expedition Report, No 76)

Processing by BODC of CTD data from cruise JC238

BODC Data Processing Procedures

The data were supplied to BODC in 44 NetCDF files, one for each cast, which were loaded into the BODC database using established BODC data banking procedures. For data recorded on two sensors, the secondary sensor was selected by the originators to be the primary information for ingestion. 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

Project Information

Marine LTSS: CLASS (Climate Linked Atlantic Sector Science)

Introduction

CLASS is a five year (2018 to 2023) programme, funded by the Natural Environment Research Council (NERC) and extended until March 2024.

Scientific Rationale

The ocean plays a vital role in sustaining life on planet Earth, providing us with both living resources and climate regulation. The trajectory of anthropogenically driven climate change will be substantially controlled by the ocean due to its absorption of excess heat and carbon from the atmosphere, with consequent impacts on ocean resources that remain poorly understood. In an era of rapid planetary change, expanding global population and intense resource exploitation, it is vital that there are internationally coordinated ocean observing and prediction systems so policy makers can make sound evidence-based decisions about how to manage our interaction with the ocean. CLASS will underpin the UK contribution to these systems, documenting and understanding change in the marine environment, evaluating the impact of climate change and effectiveness of conservation measures and predicting the future evolution of marine environments. Over the five-year period CLASS will enhance the cost-effectiveness of observing systems by migrating them towards cutting edge autonomous technologies and developing new sensors. Finally, CLASS will create effective engagement activities ensuring academic partners have transparent access to NERC marine science capability through graduate training partnerships and access to shipborne, lab based and autonomous facilities, and modelling capabilities.

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: