Metadata Report for BODC Series Reference Number 2157981

• 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 Access Policy

Open Data

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"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.

RAPID cruise JC174 CTD Instrument Description

CTD Unit and Auxillary Sensors

A Sea-Bird 11plus CTD system used on cruise JC174. This was mounted on a 24-way stainless steel rosette frame, equipped with 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.

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.

RAPID Cruise JC174 BODC CTD data processing

The CTD data were supplied to BODC as twenty-eight MStar files and converted to the BODC internal format (netCDF).

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

RAPID Cruise JC174 Originator's CTD data processing

Sampling strategy

A total of 28 complete CTD casts were performed during the cruise along approximately 26.5°N, which includes the Eastern boundary, Mid Atlantic Ridge and Western boundary sections of the RAPIDMOC array. The CTD casts provided start-point calibrations for instruments to be deployed and end-point calibrations for recovered instruments. One cast, 009, was abandoned due to the tube connecting the oxygen sensor to the pump having a loose connection.

Data processing

Raw CTD data were transferred from the Sea-Bird deck unit to a LINUX machine via Sea-Bird software. The binary files are 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 Smeed (2019).

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. The calibration of the conductivity is applied to both the upward and downward profiles of the CTD. For full details of the calibration see Smeed (2019).

Oxygen

To account for the lagged response of the sensor, a correction is applied so that the oxygen data are aligned with other CTD variables. This lag is of the order of 1 second and is normally applied by the CTD operator.

A correction for hysteresis - a time-dependent pressure-induced effect - was applied of the form

Oxynew_conc(i) = { (Oxygen_conc(i) + (Oxynew_conc(i-1) * C * D)) - (Oxygen_conc(i-1) * C) } /D

where D = 1 + H1 * (exponential(P(i)/H2)-1
C= exponential(-1 * (Time(i) - Time(i-1))/H3)
i = indexing variable
P(i) = pressure (decibars) at index point i
Time(i) = time (seconds) from start of index point i
Oxygen_conc(i) = dissolved oxygen concentration at index point i
H1 = amplitude of hysteresis correction function
H2 = function constant or curvature function for hysteresis
H3 = time constant for hysteresis (seconds)

The optimal solution was defined to be one which, when taking into consideration the heave of the upcast, minimised the root mean square difference between oxygen on the downcast and oxygen on the upcast. Outlier differences greater than 2.5 x the standard deviations were excluded from the RMS difference. Many different parameter combinations give similar results and so it is best to vary only one hysteresis parameter, the amplitude, and keep the timescale and pressure scale fixed at their default values.

The following criteria is used to determine the parameters used 1) select stations with maximum pressure of at least 4000db with total length of bottle stops not exceeding 33% of the total time for the cast, 2) find optimum parameter for each of the selected casts, 3) average the optimal parameters for the selected casts, 4) use this set of averaged parameters to evaluate hysteresis for all casts. This procedure is applied for each sensor. There was little evidence that changing the parameter improved the results,and so it was decided to keep H2 and H3 constant and vary only the amplitude of the hysteresis H1

Voltages are converted to oxygen using instrument dependent coefficients.

Comparisons with bottle data determine the calibration efficients in the form of

oxygen = (C1 + C3 * (press/5000) + C4 * (press/5000)^2) * (oxyin + C2)

where the parameters C1, C2, C3 and C4 were determined by minimising the sum of squares of the residual differences.

The following table states the cofficients for each sensor combination

References

Smeed, D. et al., (2019) RRS James Cook Cruise JC174, 20 October - 26 November 2019. RAPID cruise report for Cruise JC174. Southampton, UK: National Oceanography Centre, Southampton, 185pp. (National Oceanography Centre Cruise Report, No 59)

Project Information

Monitoring the Meridional Overturning Circulation at 26.5N (RAPIDMOC)

Scientific Rationale

There is a northward transport of heat throughout the Atlantic, reaching a maximum of 1.3PW (25% of the global heat flux) around 24.5°N. The heat transport is a balance of the northward flux of a warm Gulf Stream, and a southward flux of cooler thermocline and cold North Atlantic Deep Water that is known as the meridional overturning circulation (MOC). As a consequence of the MOC northwest Europe enjoys a mild climate for its latitude: however abrupt rearrangement of the Atlantic Circulation has been shown in climate models and in palaeoclimate records to be responsible for a cooling of European climate of between 5-10°C. A principal objective of the RAPID programme is the development of a pre-operational prototype system that will continuously observe the strength and structure of the MOC. An initiative has been formed to fulfill this objective and consists of three interlinked projects:

• A mooring array spanning the Atlantic at 26.5°N to measure the southward branch of the MOC (Hirschi et al., 2003 and Baehr et al., 2004).
• Additional moorings deployed in the western boundary along 26.5°N (by Prof. Bill Johns, University of Miami - project MOCHA) to resolve transport in the Deep Western Boundary Current (Bryden et al., 2005). These moorings allow surface-to-bottom density profiles along the western boundary, Mid-Atlantic Ridge, and eastern boundary to be observed. As a result, the transatlantic pressure gradient can be continuously measured.
• Monitoring of the northward branch of the MOC using submarine telephone cables in the Florida Straits (Baringer et al., 2001) led by Dr Molly Baringer (NOAA/AOML/PHOD) - Western Boundary Time Series (WBTS) project.

The UK-led monitoring array system was recovered and redeployed annually until 2008 under RAPID funding. From 2008 until 2015 the array continued to be serviced annually under RAPID-WATCH funding. From 2015 until 2021 the array was serviced under RAPID-AMOC funding. Since 2022 the servicing of the array has continued to be funded by the Natural Environment Research Council (NERC). The US-led projects are funded by the National Science Foundation (NSF) (MOCHA project) and NOAA Office of Climate Observations (WBTS project).

The array will be focussed on three regions, the Eastern Boundary (EB), the Mid Atlantic Ridge (MAR) and the Western Boundary (WB). The geographical extent of these regions are as follows:

• Eastern Boundary (EB) array defined as a box with the south-east corner at 23.5°N, 25.5°W and the north-west corner at 29.0°N, 12.0°W
• Mid Atlantic Ridge (MAR) array defined as a box with the south-east corner at 23.0°N, 52.1°W and the north-west corner at 26.5°N, 40.0°W
• Western Boundary (WB) array defined as a box with the south-east corner at 26.0°N, 77.5°W and the north-west corner at 27.5°N, 69.5°W

References

Baehr, J., Hirschi, J., Beismann, J.O. and Marotzke, J. (2004) Monitoring the meridional overturning circulation in the North Atlantic: A model-based array design study. Journal of Marine Research, Volume 62, No 3, pp 283-312.

Baringer, M.O'N. and Larsen, J.C. (2001) Sixteen years of Florida Current transport at 27N Geophysical Research Letters, Volume 28, No 16, pp3179-3182

Bryden, H.L., Johns, W.E. and Saunders, P.M. (2005) Deep Western Boundary Current East of Abaco: Mean structure and transport. Journal of Marine Research, Volume 63, No 1, pp 35-57.

Hirschi, J., Baehr, J., Marotzke J., Stark J., Cunningham S.A. and Beismann J.O. (2003) A monitoring design for the Atlantic meridional overturning circulation. Geophysical Research Letters, Volume 30, No 7, article number 1413 (DOI 10.1029/2002GL016776)

RAPID Climate Change - Atlantic Meridional Overturning Circulation (RAPID-AMOC)

RAPID-AMOC is an £8.4 million, 7 year (2013-2020) research programme that builds on the success of the Natural Environment Research Council's (NERC) RAPID and RAPID-WATCH programmes and will deliver a 16 year long time series of the Atlantic Meridional Overturning Circulation (AMOC).

Background

The Atlantic Meridional Overturning Circulation (AMOC) is a critical element in the energy balance of the global climate system. The AMOC consists of a near-surface, warm northward flow of ocean water, compensated by a colder southward return flow at depth. This heat is transferred from the ocean to the atmosphere at mid-latitudes, with a substantial impact on climate and, in particular, on that of the UK and northwest Europe.

Observing and understanding changes in the AMOC is critically important for identifying the mechanisms of decadal climate variability and change, and for interannual-to-decadal climate prediction. This includes predicting changes in the location, frequency and intensity of Atlantic hurricanes, storms in the North Atlantic and over Europe, shifts in tropical and European precipitation patterns, and the response of sea level to changing radiative forcing. Sustained observations are also critical for assessing the possibility of abrupt change in the AMOC that are known to occur in palaeoclimatic records.

Since 2004 the NERC RAPID and RAPID-WATCH programmes, in partnership with the National Science Foundation and the National Oceanic and Atmospheric Administration in the US, have supported an observing system to continuously measure the AMOC at 26.5°N via a trans-basin array of moored instruments. This measures the basin-wide strength and vertical structure of the AMOC, and its components.

Observations from the array have already revolutionised understanding of AMOC variability and documented its variability on seasonal to interannual timescales. The first few years of observations, demonstrated the feasibility of AMOC measurement, provided new insights into the seasonal cycle, and allowed apparent trends in previous historical 'snapshots' to be seen in the context of natural variability. RAPID-AMOC will extend the AMOC time series.

Objective

RAPID-AMOC's overall objective is to determine the variability of the AMOC, and its links to climate and to the ocean carbon sink, on interannual-to-decadal time scales

This will be achieved by the continued support of the monitoring array and supporting the use of the data in three key areas:

• Application of array data for improved ocean state estimation;
• Use of array data to understand the role of the AMOC in climate variability and predictability;
• Addition of biogeochemical sensors to the array and use to constrain biogeochemical fluxes.

Three projects have been funded to address the objectives of RAPID-AMOC:

• Reanalysis of the AMOC
• DYNamics and predictability of the Atlantic Meridional Overturning and Climate (DYNAMOC)
• Atlantic BiogeoChemical fluxes (ABC Fluxes)

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

RAPIDMOC/MOCHA Western Boundary (WB) Array

The Western Boundary Array defines a box in which moorings were deployed at the western side of the North Atlantic as part of the RAPIDMOC project and the collaborative project Meridional Overturning Circulation and Heatflux Array (MOCHA). The box region has latitudinal limits of 26° N to 27.5° N and longitudinal limits of 69.5° W to 77.5° W. Moorings have occupied this region since 2004 and are typically deployed for 6 to 18 months.

Moored data summary

Cruise data summary

During the cruises to service the moored array, a variety of data types are collected. The table below is a summary of these data. The number of CTD profiles performed on these cruises within the box region defined above is also included. Trans-Atlantic hydrographic CTD sections have also been performed since 2004 and are included in the table.

Data type ID and description

Related Fixed Station activities are detailed in Appendix 1

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:

Appendix 1: Western Boundary Array

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

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