Metadata Report for BODC Series Reference Number 1067988

• 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

RAPID Cruise D298 CTD Data Quality Report

Beam Attenuation

Please note that these data were derived using M and B coefficients found in the Sea-Bird configuration files. There is no information on whether these coefficients are recent or not. The calibration used may be well out of date and the data values should be used with caution.

Oxygen

Cast 5 recorded noisy oxygen data and has been flagged accordingly. Cast 28 has also been flagged from 771 m to the bottom of the cast as this section of the profile appears suspect.

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.

RAPID Cruise D298 CTD Instrumentation

The CTD unit was a Sea-Bird Electronics 911plus system with dual temperature and conductivity sensors.

CTD package:

Sampling device

The Sea-Bird 24 position Carousel was equipped with 10 litre sampling bottles, manufactured by Ocean Test Equipment Inc.

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 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 D298 CTD Processing

Sampling strategy

A total of 63 full depth CTD casts were performed during the cruise; a number of which had current meters attached for calibration purposes. The CTD frame was stabilised against rotation with a fin. The primary CTD sensor pair were mounted on the outer edge of the fin. The secondary sensor pair were adjacent to the CTD pressure case towards the bottom of the frame, as normal. During D298, cable problems adversely affected data quality on the primary sensor pair during stations 5, 28 and 60. The final CTD data therefore employ the primary sensor pair as the source of temperature and conductivity data for all stations except those three, where the secondary sensor pair is the source of temperature and conductivity data. Rosette bottles were fired at regular intervals throughout each profile in order to obtain salinity samples for calibration.

Sea-Bird processing

The raw CTD files were processed manually by the data originator 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). To compensate for lags in the sensor response, the oxygen sensor was shifted relative to the pressure data by 5 seconds through the ALIGNCTD function. The WILDEDIT 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, beta = 1/7, 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

After initial processing with Sea-Bird software and residual spike removal, additional PSTAR routines were applied to the 24 Hz files converting them to 1 Hz, 10 s and 2 dB versions. Following this a head and tail crop of the 1 Hz files was carried out to select the relevant data cycles from the up and down CTD casts. Bottle salinity data from the CTD upcast were used to calibrate the conductivity channel. Bottle conductivities were re-calculated from bottle salinities, CTD pressures, and primary temperatures; and were subsequently compared with CTD conductivities from the time the bottles were fired. Bottle minus conductivity was calculated for each sample and both CTD conductivity sensors. Prior to at-sea calibrations the Sea-Bird conductivity sensors differed only slightly from 'reality', and differences between sample and CTD salinities were generally less than 0.002 (excluding outliers).

The CTD oxygen sensor data were also calibrated using discrete bottle samples that had been chemically analysed for oxygen. Bottle oxygen concentrations were added to the files containing the upcast CTD sensor data from the time each bottle was fired. Oxygen concentrations were converted from µmol l^-1 to µmol kg^-1 by calculating the sample seawater density at the time of fixing using the relevant fixing temperature variable and CTD salinity. To counteract the hysteresis effect that offsets the upcast from the downcast oxygen concentrations, the upcast CTD oxygen data were replaced with the downcast data. This was achieved by tracing water masses between the up and down casts along density and potential temperature surfaces. Finally, the bottle oxygen concentrations (O_bot) were compared with the equivalent downcast CTD oxygen concentrations (O_dCTD) and the differences regressed as a linear function of pressure. The following equation was used to calibrate the downcast CTD oxygen profiles to their 'true' concentrations:

O_bot - O_dCTD = a +bP

Where a + b are offset and slope parameters of the linear fit, and p is pressure.

Full details of all processing and calibrations carried out by the data originator can be found in the RRS Discovery Cruise D298 cruise report

BODC post-processing and screening

Reformatting

The 2 dB version of the data were converted from PSTAR into BODC's internal format (a NetCDF subset) to allow use of in-house visualisation tools.

Screening

Reformatted CTD data were visually checked using the in-house editor EDSERPLO. Suspect datacycles were flagged with quality control flags, where appropriate.

Banking

Once BODC quality control screening was complete, the CTD downcasts were banked into BODC's National Oceanographic Database.

Project Information

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.

RAPID - Cape Farewell and Eirik Ridge: Interannual to Millennial Thermohaline Circulation Variability

This project was funded under the NERC Rapid Climate Change Programme, grant number NER/T/S/2002/00453. Dr. Sheldon Bacon (Southampton Oceanography Centre) was the Principal Investigator, with co-Investigators from the University of Southampton, Prof. D. A. Stow and Dr. E. J. Rohling. The project started in December 2003 and ended in November 2008.

The project used a combination of hydrography and palaeoceanography measurements to determine the spectrum of variability of the Deep Western Boundary Current, on timescales from days to millennia. The project focused on deglacial to Holocene variability; in particular, seeking to characterise the onset and endings of three cold periods: the Younger Dryas (YD; 12.5-11.5 ka BP), the ~8.2 ka event, and the Little Ice Age (LIA; 16th-19th century AD).

The objectives of the project included:

• Defining the THC response to Holocene climate variability by a highly resolved investigation of palaeoceanographic/climate proxies in sediment cores
• Developing high-resolution sediment proxies for bottom current speed
• Absolute calibration of sediment proxies for bottom current speed
• Defining the relationship between drift construction and the bottom current regime
• Improved definition of present-day ocean circulation and climate

Most of the fieldwork was carried out on 2 cruises in the Cape Farewell and Irminger Sea vicinity:

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: