Metadata Report for BODC Series Reference Number 1012650

• 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 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

RAPID Cruise D344 CTD instrument description

CTD unit and auxiliary sensors

The CTD system used on cruise D344 was a NOC 24-way stainless steel frame system (s/n SBE CTD1415) consisting of a Sea-Bird 911 plus, with a Sea-Bird 32 carousel. The water samples were Ocean Test Equipment 10L ES-115B and were used in alternate positions on the CTD frame. This was to allow moored instruments to be strapped to the frame for calibration purposes. During the cruise various problems with sensors required them to be replaced on the CTD frame (see Section 11.1 of the D344 cruise report). The table below shows which sensors were attached to the CTD frame and on which casts.

The salinity samples from the CTD were analysed during the cruise using a Guildline Autosal model 8400B(serial number 68958).

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.

BODC CTD Screening

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

• Irregularities such as infeasible values
• Inconsistencies between related information. For example:
  • Deepest CTD data cycle is significantly greater than the depth of the sea floor.
  • Times of the cruise and the start/end of the data series.
  • Length of the record, number of data cycles, cycle interval, clock error and the period over which data were collected.
  • Parameters stated as measured and the parameters actually present in the data series.
• Originator's comments on instrument/sampling device performance and data quality.

Documents are written by BODC highlighting irregularities that cannot be resolved.

Data cycles are inspected using depth series plots of all parameters. These presentations undergo screening to detect infeasible values within the data cycles themselves and inconsistencies when comparing adjacent data sets displaced with respect to depth, position or time.

Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value.

The following types of irregularity, each relying on visual detection in the time series plot, are amongst those that may be flagged as suspect:

• Spurious data at the start or end of the record where the instrument was recording in air
• Obvious spikes occurring in the data due electrical problems
• Constant, or near-constant, data channels

If a large percentage of the data is affected by irregularities, deemed abnormal, then instead of flagging the individual suspect values, a caution may be documented.

The following types of inconsistency are detected automatically by software:

• Data points with values outside the expected range for the parameter, as defined by the BODC parameter usage vocabulary.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought, and where necessary, documented. This covers inconsistencies in the following:

• Maximum and minimum values of parameters (spikes excluded).
• Anomalous readings due to the CTD package being bounced through temperature and/or salinity gradients.

This screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC's making are not introduced.

RAPID Cruise D344 BODC CTD data processing

The data arrived at BODC in 27 MSTAR format files representing the CTD casts conducted during cruise D344. The data contained in the files are the downcast data averaged to a 2db pressure grid. The casts were reformatted to BODC's internal NetCDF format. The following table shows the mapping of variables within the MSTAR files to appropriate BODC parameter codes:

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, and missing data marked by setting both the data to an appropriate value and setting the quality control flag.

Detailed metadata and documentation were compiled and linked to the data.

RAPID Cruise D344 Originator's CTD data processing

Sampling Strategy

A total of 27 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. On each cast, up to 12 SBE37 MicroCATs were attached to the frame for calibration purposes. The CTD casts provided start-point calibrations for instruments to be deployed and end-point calibrations for recovered instruments. For recovered instruments that were re-deployed, the post-deployment cast provided a pre-deployment calibration. The instruments were set to the fastest sampling rate and the CTD lowered as normal. On the upcast, the bottle stops were increased to 5 minutes to allow time for stabilisation and the provision of more accurate data. To allow the instruments to be attached to the CTD frame using bespoke attachments, up to 12 sample bottles were removed on all casts.

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 v7.18). Physical units were calculated from the frequency data using the manufacturer's calibration routines and the data converted to ASCII format. The ASCII files were converted to MSTAR format and MEXEC programs were run to reduce the frequency of the data from 24Hz to 1Hz, and for the downcast to be averaged to a 2db pressure grid. A calibration was produced for the CTD primary conductivity sensor 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 Cunningham et al. (2010).

Field Calibrations

Independent salinity samples, obtained from the bottles on the CTD frame, were used to calibrate the CTD salinity data. Bottle samples with incorrect conductivities were identified and removed from the calibration. Data points were excluded if the residual (bottle conductivities minus CTD conductivities) was outside the limits -0.002 to 0.008 mS/cm for casts 3-27 and exceeded 0.015 mS/cm for casts 1 and 2. Also if the residual was larger than 3 standard deviations of the new station mean, the data were excluded. Out of 310 samples, 16 were removed by these criteria.

A slope correction to account for sensor drift was applied such that C_CTDcorrected₁=C_CTD*K. Due to a change in the primary conductivity sensor (after cast 2) and grouping residuals that have similar offsets, K was calculated for groups of casts namely, casts 1-2, 4-7, 8-13 and 14-27, the values of K being 1.000232, 1.000043, 1.000010 and 1.000027, respectively. Cast 3 was excluded from the block averaging because it was a shallow cast with short bottle stops. Hence, the K value from casts 4-7 was applied to cast 3.

A quadratic fit of residual difference against pressure was then applied to remove the increase in residual with depth. The quadratic fit applied was

Δ_C = C_bot - C_CTD = a₂p² + a₁p + a₀

where a₂=3.7 x 10^-11 ± 2.5 x 10^-11 mS cm^-1db^-2, a₁= 2.0 x 10^-7 ± 1.4 x 10^-7mS cm^-1db^-1 and a₀=-7.1 x 10^-4 ± 1.5 x 10^-4 mS/cm.

References

Cunningham, S.A., Wright, P.G. (ed.) (2010) RRS Discovery Cruise D344, 21 Oct-18 Nov 2009. RAPID Mooring cruise report. Southampton, UK, National Oceanography Centre, Southampton, 225pp. (National Oceanography Centre Southampton Cruise Report, 51)

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) 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).

The entire monitoring array system created by the three projects will be recovered and redeployed annually until 2008 under RAPID funding. From 2008 until 2014 the array will continue to be serviced annually under RAPID-WATCH funding.

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- Will the Atlantic Thermohaline Circulation Halt? (RAPID-WATCH)

RAPID-WATCH (2007-2014) is a continuation programme of the Natural Environment Research Council's (NERC) Rapid Climate Change (RAPID) programme. It aims to deliver a robust and scientifically credible assessment of the risk to the climate of UK and Europe arising from a rapid change in the Atlantic Meridional Overturning Circulation (MOC). The programme will also assess the need for a long-term observing system that could detect major MOC changes, narrow uncertainty in projections of future change, and possibly be the start of an 'early warning' prediction system.

The effort to design a system to continuously monitor the strength and structure of the North Atlantic MOC is being matched by comparative funding from the US National Science Foundation (NSF) for the existing collaborations started during RAPID for the observational arrays.

Scientific Objectives

• To deliver a decade-long time series (2004-2014) of calibrated and quality-controlled measurements of the Atlantic MOC from the RAPID-WATCH arrays.
• To exploit the data from the RAPID-WATCH arrays and elsewhere to determine and interpret recent changes in the Atlantic MOC, assess the risk of rapid climate change, and investigate the potential for predictions of the MOC and its impacts on climate.

This work will be carried out in collaboration with the Hadley Centre in the UK and through international partnerships.

Mooring Arrays

The RAPID-WATCH arrays are the existing 26°N MOC observing system array (RAPIDMOC) and the WAVE array that monitors the Deep Western Boundary Current. The data from these arrays will work towards meeting the first scientific objective.

The RAPIDMOC array consists of moorings focused in three geographical regions (sub-arrays) along 26.5° N: Eastern Boundary, Mid-Atlantic Ridge and Western Boundary. The Western Boundary sub-array has moorings managed by both the UK and US scientists. The other sub-arrays are solely led by the UK scientists. The lead PI is Dr Stuart Cunningham of the National Oceanography Centre, Southampton, UK.

The WAVE array consists of one line of moorings off Halifax, Nova Scotia. The line will be serviced in partnership with the Bedford Institute of Oceanography (BIO), Halifax, Canada. The lead PI is Dr Chris Hughes of the Proudman Oceanographic Laboratory, Liverpool, UK.

All arrays will be serviced (recovered and redeployed) either on an annual or biennial basis using Research Vessels from the UK, US and Canada.

Modelling Projects

The second scientific objective will be addressed through numerical modelling studies designed to answer four questions:

• How can we exploit data from the RAPID-WATCH arrays to obtain estimates of the MOC and related variables?
• What do the observations from the RAPID-WATCH arrays and other sources tell us about the nature and causes of recent changes in the Atlantic Ocean?
• What are the implications of RAPID-WATCH array data and other recent observations for estimates of the risk due to rapid change in the MOC?
• Could we use RAPID-WATCH and other observations to help predict future changes in the MOC and climate?

Rapid Climate Change (RAPID) Programme

Rapid Climate Change (RAPID) is a £20 million, six-year (2001-2007) programme of the Natural Environment Research Council (NERC). The programme aims to improve our ability to quantify the probability and magnitude of future rapid change in climate, with a main (but not exclusive) focus on the role of the Atlantic Ocean's Thermohaline Circulation.

Scientific Objectives

• To establish a pre-operational prototype system to continuously observe the strength and structure of the Atlantic Meridional Overturning Circulation (MOC).
• To support long-term direct observations of water, heat, salt, and ice transports at critical locations in the northern North Atlantic, to quantify the atmospheric and other (e.g. river run-off, ice sheet discharge) forcing of these transports, and to perform process studies of ocean mixing at northern high latitudes.
• To construct well-calibrated and time-resolved palaeo data records of past climate change, including error estimates, with a particular emphasis on the quantification of the timing and magnitude of rapid change at annual to centennial time-scales.
• To develop and use high-resolution physical models to synthesise observational data.
• To apply a hierarchy of modelling approaches to understand the processes that connect changes in ocean convection and its atmospheric forcing to the large-scale transports relevant to the modulation of climate.
• To understand, using model experimentation and data (palaeo and present day), the atmosphere's response to large changes in Atlantic northward heat transport, in particular changes in storm tracks, storm frequency, storm strengths, and energy and moisture transports.
• To use both instrumental and palaeo data for the quantitative testing of models' abilities to reproduce climate variability and rapid changes on annual to centennial time-scales. To explore the extent to which these data can provide direct information about the thermohaline circulation (THC) and other possible rapid changes in the climate system and their impact.
• To quantify the probability and magnitude of potential future rapid climate change, and the uncertainties in these estimates.

Projects

Overall 38 projects have been funded by the RAPID programme. These include 4 which focus on Monitoring the Meridional Overturning Circulation (MOC), and 5 international projects jointly funded by the Netherlands Organisation for Scientific Research, the Research Council of Norway and NERC.

The RAPID effort to design a system to continuously monitor the strength and structure of the North Atlantic Meridional Overturning Circulation is being matched by comparative funding from the US National Science Foundation (NSF) for collaborative projects reviewed jointly with the NERC proposals. Three projects were funded by NSF.

A proportion of RAPID funding as been made available for Small and Medium Sized Enterprises (SMEs) as part of NERC's Small Business Research Initiative (SBRI). The SBRI aims to stimulate innovation in the economy by encouraging more high-tech small firms to start up or to develop new research capacities. As a result 4 projects have been funded.

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: