Metadata Report for BODC Series Reference Number 1058217
No Problem Report Found in the Database
RAPID Cruise D279 CTD Data Quality Report
General data quality
Frequent looping occurred in the 1 Hz data, probably as a consequence of ship's heave. In cases where looping was particularly severe, flags were assigned to the data values. As flagged data are excluded from the binning process, some profiles required interpolation across the bin. Interpolated values are indicated by the presence of a flag alongside the data value.
A significant number of data cycles were excluded from the beginning of the downcasts where the CTD was logging on deck.
It should also be noted that the data originator specified a preference for the primary salinity and temperature data.
All primary salinity data were calibrated against salinity samples. Data from the secondary sensor were not calibrated independently and consequently are not deemed to have the same reliability. Therefore the data from the secondary sensor has been excluded from the series. Secondary salinity was not logged during Casts 3 - 6.
Temperature for both channels was checked against the independent Sea-Bird 35 deep ocean standard temperature sensor. Secondary temperature was not logged during Casts 3 - 6. Data from the secondary sensor were excluded from the series as the data originator expressed a preference for data from the primary sensor.
Spikes occurred in the pressure channel of Cast 1, which were flagged suspect.
Beam attenuation was not measured for Cast 25 to Cast 125, inclusive.For Casts 1 to 24, when the transmissometer was logging, it is not known whether calibration air readings were made, so the data are qualitative at best. On screening the casts, it was noticed that the profiles were not typical for the deep ocean and did not display the expected mid-water minimum or profile shape. Additionally, the values appear too high in most cases. Taking all of this into account, the data are likely to be unreliable and should be used with caution.
Due to problems encountered calibrating this sensor, including the discovery of a torn sensor membrane post-cruise, the data originator considers this whole data set suspect. Oxygen was not recorded during Casts 2 to 5 and Cast 7. Cast 6 logged negative values throughout.
Casts 23 and 25 have no chlorophyll channel. Several casts returned bad data in parts of the profile, resulting in null portions of the profile as follows: Casts 31, 32 and 35 in top 200 m; Cast 33 between 700 and 950 m; Casts 37, 46, 48 and 50 after 4000 m.
Several casts contain slightly negative concentrations, which is due to the presence of a small offset or error in the calibration applied and affects those casts where very low concentrations of chlorophyll are present. The casts affected include Cast 18, Cast 20, Cast 24, Casts 31 and 32, Casts 37 to 115, and Casts 117 to 120. All negative values have been flagged, where appropriate.
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."
RAPID Cruise D279 CTD Instrumentation
The CTD unit was a Sea-Bird Electronics 911plus system with dual temperature and conductivity sensors plus oxygen sensor, fluorometer, transmissometer, optical backscatter and altimeter. Also attached to the frame were 3 RDI ADCPs. Details of these sensors are documented in the table below. The light backscattering sensor was disconnected after Cast 23, and no output from this instrument or the ADCPs was included in the final data set.
|Sensor||Serial number||Last calibration date|
|Digiquartz temperature compensated pressure sensor||78958||17/06/2003|
|Sea-Bird 4 conductivity sensor (primary)||2407 (Casts 1 - 37, 94 - 125)||29/01/2004|
|2450 (Casts 38 - 93)||29/01/2004|
|Sea-Bird 4 conductivity sensor (secondary)||2840 (Casts 1 - 37, 109 - 125)||29/01/2004|
|2637 (Casts 38-108)||29/01/2004|
|Sea-Bird 3 temperature sensor (primary)||2919 (Casts 1-37)||29/01/2004|
|2880 (Casts 38-93)||29/01/2004|
|2758 (Casts 94-125)||29/01/2004|
|Sea-Bird 3 temperature sensor (secondary)||4116 (Casts 1-37)||29/01/2004|
|2758 (Casts 38-93)||29/01/2004|
|2880 (Casts 94-125)||29/01/2004|
|Chelsea Aquatracka MKIII fluorometer||88-2360-108 (Casts 1-37)||11/11/2002|
|088163 (Casts 38-125)||13/11/2002|
|Chelsea MKII Alphatracker transmissometer||161048||03/05/2001|
|Sea Tech light back-scattering sensor||400||28/04/1998|
|Sea-Bird 43 dissolved oxygen sensor||0619||26/02/2004|
|SBE Deep Ocean Standards Thermometer||37||11/02/2004|
|RDI Broadband 150 KHz ADP (downward looking)||1308||-|
|RDI 300 KHz Workhorse ADP (downward looking)||3726||-|
|RDI 300 KHz Workhorse ADP (upward looking)||1881||-|
The Sea-Bird 24 position Carousel was equipped with 10 litre sampling bottles, manufactured by Ocean Test Equipment Inc.
More than 2600 salinity samples from the CTD were analysed during the cruise using a Guildline 8400B salinometer.
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.
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.
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 for the SBE 9 plus underwater unit are listed below:
|Parameter||Range||Initial accuracy||Resolution at 24 Hz||Response time|
|Temperature||-5 to 35°C||0.001°C||0.0002°C||0.065 sec|
|Conductivity||0 to 7 S m-1||0.0003 S m-1||0.00004 S m-1||0.065 sec (pumped)|
|Pressure||0 to full scale (1400, 2000, 4200, 6800 or 10500 m)||0.015% of full scale||0.001% of full scale||0.015 sec|
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.
Chelsea Technologies Group ALPHAtracka and ALPHAtracka II transmissometers
The Chelsea Technologies Group ALPHAtracka (the Mark I) and its successor, the ALPHAtracka II (the Mark II), are both accurate (< 0.3 % fullscale) transmissometers that measure the beam attenuation coefficient at 660 nm. Green (565 nm), yellow (590 nm) and blue (470 nm) wavelength variants are available on special order.
The instrument consists of a Transmitter/Reference Assembly and a Detector Assembly aligned and spaced apart by an open support frame. The housing and frame are both manufactured in titanium and are pressure rated to 6000 m depth.
The Transmitter/Reference housing is sealed by an end cap. Inside the housing an LED light source emits a collimated beam through a sealed window. The Detector housing is also sealed by an end cap. A signal photodiode is placed behind a sealed window to receive the collimated beam from the Transmitter.
The primary difference between the ALPHAtracka and ALPHAtracka II is that the Alphatracka II is implemented with surface-mount technology; this has enabled a much smaller diameter pressure housing to be used while retaining exactly the same optical train as in the Mark I. Data from the Mark II version are thus fully compatible with that already obtained with the Mark I. The performance of the Mark II is further enhanced by two electronic developments from Chelsea Technologies Group - firstly, all items are locked in a signal nulling loop of near infinite gain and, secondly, the signal output linearity is inherently defined by digital circuitry only.
Among other advantages noted above, these features ensure that the optical intensity of the Mark II, indicated by the output voltage, is accurately represented by a straight line interpolation between a reading near full-scale under known conditions and a zero reading when blanked off.
For optimum measurements in a wide range of environmental conditions, the Mark I and Mark II are available in 5 cm, 10 cm and 25 cm path length versions. Output is default factory set to 2.5 volts but can be adjusted to 5 volts on request.
Further details about the Mark II instrument are available from the Chelsea Technologies Group ALPHAtrackaII specification sheet.
RAPID Cruise D279 CTD Processing
A total of 125 full depth CTD casts were performed during the cruise. Rosette bottles were fired at regular intervals throughout each profile in order to obtain salinity samples for calibration. In addition, samples were taken from the bottles for analysis of dissolved oxygen, nitrate, silicate, phosphate, CFCs, carbon tetrachloride, total alkalinity and partial pressure of carbon dioxide.
On Cast 17 the winch scrolling gear follower failed with the CTD 26 m off the sea bed. The CTD touched the bottom and had to be towed to deeper water. The duration of this cast was significantly longer than expected as a consequence.
Sea-Bird processing by data originator
The raw CTD files were processed manually through Sea-Bird SBE Data Processing software. 24 Hz binary (.DAT) files were converted to engineering units and nominal values using manufacturer's calibration coefficients (DATCNV). ALIGN CTD was run to advance oxygen by 5 seconds relative to pressure. Coefficients for temperature and conductivity were set to 0, as advancement of these parameters was carried out by the deck unit. The WILD EDIT function was subsequently used to reduce the amount of noise in all CTD profiles. To compensate for conductivity cell thermal mass effects, the files were run through CELLTM, using alpha = 0.03, 1/beta = 7, typical values for this CTD model given in the Sea-Bird literature. The final stage of Sea-Bird processing carried out was TRANSLATE, which generates ASCII versions of the binary .CNV data files.
PSTAR processing by data originator
After initial processing with Sea-Bird software, additional routines were applied to the 24 Hz files in PSTAR and subsequently worked through to the 1 Hz and 10 s versions. Bottle salinity data from the CTD upcast were used to calibrate the primary CTD conductivity channel. Bottle conductivities were re-calculated from bottle salinities and compared with CTD conductivities from the time the bottles were fired. A slope correction was applied to the sensor, as a result of this investigation, to account for sensor drift. The calibration data set excluded samples where (Bottle - CTD conductivity) exceeded specified limits.
Further analysis, following slope correction, revealed a pressure dependence in (Bottle - CTD conductivity) during Casts 38 - 93 and 94 - 120. The pressure dependence in the former set of casts was addressed by favouring data from the secondary sensors, and through application of linear and quadratic pressure fits to the upper and lower water column respectively. The latter set of casts were adjusted by application of pressure fits alone, without the swapping of sensor data.
The final stage of calibration was the addition of a station by station salinity offset to the primary CTD salinity channel, following removal of sample data outliers. No salinity correction was applied to Cast 119 due to significant scatter in the (Bottle - CTD conductivity) values.
BODC post-processing and screening
The 1 Hz version of the data were converted from PSTAR into BODC internal format (QXF) to allow use of in-house visualisation tools. In addition to reformatting, the transfer program (tr360) converted dissolved oxygen from µmol kg-1 to µmol l-1. The following table shows how the variables within the original PSTAR file were mapped to appropriate parameter codes;
|Parameter||Parameter units||Parameter code||Comments|
|Beam attenuation||m-1||ATTNMR01||Channel present in casts 1-24 only. Profiles are not typical and data are deemed suspect by BODC.|
|Chlorophyll-a||mg m-3||CPHLPM01||Channel present in casts 1-22, 24 and 26-125 only. Manufacturer's calibration applied.|
|Dissolved oxygen||µmol l-1||DOXYSU01||Channel present in casts 1, 3, 4 and 8-125 only. Deemed suspect by data originator.|
|Potential temperature (UNESCO)||°C||POTMCV01||Regenerated at BODC.|
|Pressure||dbars||PRESPR01||Manufacturer's calibration applied.|
|Salinity (Primary)||-||PSALCC01||Calibrated by data originator with discrete salinity samples.|
|Sigma-theta (UNESCO SVAN)||Kg m-3||SIGTPR01||Regenerated at BODC.|
|Temperature (Primary)||°C||TEMPCC01||Verification by data originator with SBE35 thermometer.|
Reformatted CTD data were transferred onto a graphics workstation for visualisation using the in-house editor EDSERPLO. Downcasts and upcasts were differentiated and the limits flagged. No data vales were edited or deleted.
Once BODC quality control screening was complete, the CTD downcasts were loaded into BODC's ocean database under the ORACLE Relational Database Management System.At this stage, the data were binned to 2 dbar. Temperature and salinity data from the secondary sensors were excluded from the final data series as the data originator expressed a preference for data from the primary sensors.
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.
- 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.
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.
Monitoring the Meridional Overturning Circulation at 26.5N (RAPIDMOC)
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
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)
|Principal Scientist(s)||Stuart A Cunningham (Southampton Oceanography Centre)|
Complete Cruise Metadata Report is available here
No Fixed Station Information held for the Series
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||Below detection limit|
|>||In excess of quoted value|
|A||Taxonomic flag for affinis (aff.)|
|B||Beginning of CTD Down/Up Cast|
|C||Taxonomic flag for confer (cf.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|I||Taxonomic flag for single species (sp.)|
|K||Improbable value - unknown quality control source|
|L||Improbable value - originator's quality control|
|M||Improbable value - BODC quality control|
|O||Improbable value - user quality control|
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|