Metadata Report for BODC Series Reference Number 2023436

• 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

JC112 CTD Data Quality Report

The primary and secondary temperature, conductivity, and salinity channels were deemed of similar quality by the originator. In this case, one channel was not chosen, instead the data are the result of the averaging of the primary and secondary channels. As this is not standard practise data should be viewed with caution.

Screening and Quality Control

During BODC quality control, data were screened using in house visualisation software and any obvious outliers and spikes were looked at in closer detail and flagged if necessary.

Temperature (TEMPST01) and Conductivity (CNDCST01)

M flags were applied to several series where anomalous data were found. This includes spikes caused by the averaging of the primary and secondary channels. Associated parameters (DOXYSC01, PSALST01, and SVELCA01) were also flagged.

DOXYSC01

M flags were applied to several series where anomalous data were found, especially if spikes were identified but no similar features were identified in the Temperature or Conductivity.

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.

JC112 CTD Instrumentation

The Sea-Bird Scientific SBE911plus CTD was mounted on a rosette with a SBE32 carousel water sampler and 24 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.

JC112 BODC CTD Data Processing

The data arrived at BODC in ascii format representing the data collected from CTDs deployed at different stations along the Panama Basin during cruise JC112. No changes were made to the data themselves. The following table shows the mapping of variables within the ascii data file to appropriate BODC parameter codes:

The reformatted data were visualised using in-house software. Any suspect data were flagged, using the BODC quality control flags.

JC112 Originator CTD Data Processing

Sampling Strategy

A total of 87 CTD casts were deployed during OSCAR cruise JC112, of which one was a test cast and another to complete a previous cast. In addition, 20 of the 87 casts were tow-yo casts below 3000 m.

Data Processing

CTD data processing procedures were as follows:

• Processing was carried out using Sea-Bird Electronics data processing software (Version Seasave V 7.23.1).
• The raw .hex files were converted to .cnv and .ros files.
• The pressure data were filtered by a low-pass filter of 0.15 seconds.
• The conductivity data were filtered to remove conductivity cell thermal mass effects (alpha=0.03, 1/beta=7).
• Bad scans marked by pressure slowdowns (slower than the fixed minimal velocity of 0.25m/s) or pressure reversal, were given a flag value of -9.990e-29. All of the data were then averaged over 1 dbar bins.
• One of each temperature, salinity, and conductivity channels were selected.
• Oxygen concentration values were converted to umol/L.
• Sound velocity was derived using the UNESCO algorithm.
• Data was split into up and down cast. Only down cast datafiles were kept. Tow-yo data were split into files, one for each down cast.
• Ascii files created from the .cnv files.

CTD Conductivity Calibration

The two conductivity sensors were calibrated using water bottle samples that were taken at each cast at discrete intervals: around 100 m apart for the shallower levels, and 250 m to 500 m apart at the deeper levels. In total, approximately 1560 water samples were analysed in the lab using Autosalinograph for conductivity comparison with CTD sensor measurements. Comparing the two CTD measured conductivities and the calibrated bottle conductivity estimates, the outliers were identified as values that differed more than 0.01 mS/cm. The final CTD calibration used 1545 "good" data points, after removing outliers. The linear regression of autosal calibrated data versus CTD uncalibrated data revealed: C_calibr = 0.9996 x C_insitu1 + 0.01170 mS/cm for CTD sensor 1, and C_calibr = 1.0003 x C_insitu2 - 0.01027 mS/cm for CTD sensor 2. Above 2000 m depth, the water column is much less stable leading to large differences between autosal and in-situ conductivity measurements, more than 0.005 mS/cm. Thus, higher precision of CTD conductivity calibration is achieved sampling waters below about 2000 meters, i.e. below water masses of shallow overturning circulation. In addition, the difference between the two CTD conductivity sensors was tested in a profile with 20-minute stops at different depths, designed to calibrate MicroCATs. The difference was less than 0.001 mS/cm most of the time in stable waters, however, in the presence of turbulence, the difference could reach almost 0.005 mS/cm. In the tested profile, sensor 1 was more stable than sensor 2.

CTD Oxygen Calibration

The CTD oxygen sensors were calibrated using water bottle samples taken at 62 stations. The higher the oxygen concentration, the higher the mismatch is between in-situ and corresponding lab oxygen values. The range of oxygen concentrations up to 100 umol/L is better sampled and less noisy than the upper range of oxygen concentrations, therefore two separate linear regression fits to the data were performed, one below and one above 100 umol/L. The CTD oxygen sensor calibration results are: Ox_calibr = 1.085 x Ox_insitu + 0.161 umol/L for low oxygen concentrations (<100 umol/L), and Ox_calibr = 1.000 x Ox_insitu + 8.805 umol/L for high oxygen concentrations (>100 umol/L).

Project Information

Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR)

Background

The cooling of young oceanic crust is the main physical process responsible for removing heat from the solid Earth to the hydrosphere. Close to the mid-ocean ridge rapid cooling is dominated by hydrothermal circulation of seawater through the porous and fractured basalt crust. This hydrothermal fluid is then discharged into the ocean mainly along the ridge. Once in the ocean, released heated seawater mixes with the ambient cold water to form a plume, which provides a mechanism to lift the densest waters away from the bottom boundary layer. These waters are then more readily available for further mixing and heating as part of the global thermohaline circulation system.

The data collected as part of the interdisciplinary OSCAR project will be used to investigate the effects of heat loss and hydrothermal circulation in both the solid Earth and the ocean.

The aim is to:

1. Characterise how heat from the interior of the Earth is transported across the crust into the ocean by hydrothermal flows
2. Determine the impact the hydrothermal and geothermal fluxes have on the circulation of the abyssal ocean and on the evolution of the oceanic crust.

With this aim, the data will be used to derive a new integrated model of the ocean and hydrothermal circulations at active ocean ridges and ridge flanks. The model will be constrained by geophysical, geological, and physical oceanography data and include fluxes through a permeable seabed. These data and resultant models will set a new benchmark for integrated multi-physics experiments. They will result in a new understanding of the fluid and heat fluxes at ocean ridges and a better understanding of what geophysical and oceanographic data actually resolve in the context of an oceanic axial ridge setting. The result is also a predictive model that can be applied to similar ocean ridge systems world-wide.

Fieldwork

Data collection took place in the Panama Basin, bounded in the north-west by the Cocos Ridge, by the Carnegie Ridge in the south and by South and Central America in the east and north, respectively. Measurements were collected during RRS James Cook cruises JC112 and JC113 (05/12/2014 to 16/01/2015), RRS James Cook cruise JC114 (22/01/2015 to 08/03/2015) and RV Sonne cruise SO328 (06/02/2015 to 06/03/2015). Data were collected using Bottom Pressure Recorder, Acoustic Doppler Current Profiler (ADCP), Magnetotelluric Lander, CTD, Vertical Microstructure Profiler, Synthetic Aperture Radar, Ocean-bottom seismograph and Multibeam echosounder. Measurement of salinity, oxygen and helium were also made and zooplankton samples collected with vertical net casts.

Participants

• Professor Richard W Hobbs (Principal Investigator - Parent Grant) Durham University
• Professor Christine Peirce (Co-Investigator) Durham University
• Professor Christopher J Ballentine (Co-Investigator) University of Oxford
• Professor Joanna V Morgan (Co-Investigator) Imperial College London
• Dr Miguel Morales Maqueda (Principal Investigator - Child Grant) Newcastle University
• Dr David A Smeed (Co-Investigator - Child Grant) National Oceanography Centre
• Dr Vincent CH Tong (Principal Investigator - Child Grant) Birkbeck College

Funding

This project was funded by Natural Environment Research Council parent grant NE/I027010/1 and child grants NE/I022868/1, NE/I022868/2, NE/I022957/1, and NE/I022957/2, entitled 'OSCAR - Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge', with the former, parent grant led by Professor Richard W Hobbs, Durham University, and the latter child grants led by Dr Miguel Morales Maqueda, Newcastle University and Dr Vincent CH Tong, Birkbeck College.

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: