Metadata Report for BODC Series Reference Number 1066205

• 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 CD159 CTD Data Quality Report

Pressure

There were lots of problems with the pressure channel spiking during the downcasts of casts 12, 14 and 20. Extensive flagging was required where this occurred. Many of the other channels gave erroneous readings during these periods, which required flagging.

Beam attenuation

The user should be aware that the lack of more recent air readings for this cruise means that the air readings from the previous cruise may not be applying an accurate correction. The data for cast 1 are too high by approximately 0.1 m ^-1. This may be due to dirt on the optical window of the sensor. There is an apparent negative offset present for the remaining casts, with beam attenuation values reading too low. Flagging of data spikes was required in many casts.

Turbidity

The data in this channel are relatively noisy. As a result, only the major spikes are flagged 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 CD159 CTD Instrumentation

The CTD unit was a Sea-Bird Electronics 911plus system. Details of the sensors on the CTD package are shown in the table below.

Sampling device

Sea-Bird 24 position Carousel 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 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.

Sea Tech Light Back-Scatter sensor

The instrument projects light into the sample volume using two modulated 880 nm Light Emitting Diodes. Light back-scattered from the suspended particles inthe water column is measured with a solar-blind silicon detector. A light stop between the light source and the light detector prevents the measurement of direct transmitted light so that only back-scattered light from suspended particles in water are measured.

The sensor has two ranges permitting the user to measure nearly all suspended particle concentrations found in open ocean or coastal waters. Range for the measurement of suspended particle concentration in water will be approximately 10 mg l^-1 if High_Gain is selected. If Low-Gain is selected full scale will be a factor of 3.3 higher or approximately 33 mg l^-1.

Specifications

Further details can be found in the manufacturer's specification sheet.

RAPID Cruise CD159 CTD Processing

Sampling strategy

A total of 20 CTD casts were taken during the cruise. Rosette bottles were fired at regular intervals throughout each profile in order to obtain salinity samples for calibration. Some of the rosette bottles were fired solely to obtain samples for analysis of alkalinity and isotopic composition (oxygen and carbon) of seawater. An under-CTD mini-corer was attached to the CTD frame for over half of the casts in order to obtain sediment samples.

Sea-Bird processing

The raw CTD files were supplied to BODC and processed through Sea-Bird SBE Data Processing software version 5.34. Binary (.DAT) files were converted to engineering units and ASCII format (.CNV) using the DATCNV program. The configuration (.CON) file sourced by DATCNV was altered to enter coefficients of M and B, allowing calibration of the Aquatracka Mk 2 transmissometer (SN 161-2642) with air readings taken during the previous cruise, CD158. M and B are calculated according to SBE application note no. 7:

Where Tw is the percent transmission for pure water for the instrument (90.2%); W0 is the voltage output in pure water (4.205 volts); A0 is the factory air voltage (4.660 volts); Y0 is the factory blocked path voltage (0.027 volts); A1 is the maximum air voltage measured on the previous cruise (4.8352 volts); Y1 is the current blocked path voltage (0.0330 volts). For this cruise, M and B were calculated to be 20.8286 and -0.6873, respectively. No calibration information was available for the additional transmissometer, and the data in this channel remained as raw voltages and were subsequently dropped from the series. All data preceding the top of each downcast (i.e. soaking periods) were excluded.

Sea-Bird bottle files (.BTL), with information on pressure and other logged readings at the time of bottle firing, were generated by running BOTTLESUM. No lag in conductivity was found when random casts were checked. Sea-Bird software program ALIGNCTD was run to advance oxygen by 3 seconds (within the typical range given in the Sea-Bird manual). No adjustment was made to the temperature channel as the fast sensor response time renders this unnecessary, according to the Sea-Bird literature.

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. FILTER was run on the pressure channel using the recommended time filter of 0.15 seconds before running LOOPEDIT. The latter program was not run on a number of casts (1, 7, 8, 12-14 and 20) due to the presence of pressure spikes in the down and upcasts. Running LOOPEDIT on these casts would have resulted in the removal of good quality data. Subsequently, salinity, density and oxygen concentration were calculated and added to the output files using the DERIVE program, prior to the files being averaged to 0.5 second intervals using BINAVERAGE. The final Sea-Bird program to be run was STRIP. This removed the salinity, oxygen and density channels which were created when DATCNV was run at the start of the processing sequence.

BODC post_processing and screening

The data were converted from ASCII format into BODC internal format to allow use of in-house visualisation tools. In addition to reformatting, the transfer program converted dissolved oxygen from ml l^-1 to µmol l^-1 by multiplying the original value by 44.66. The following table shows how the variables within the original files were mapped to appropriate BODC parameter codes;

Calibrations

Salinity

Independent bottle salinity values were used to calibrate both CTD salinity sensors. 66 salinity samples from the CTD were analysed during the cruise using a Portasal salinometer. The salinity values derived from the analysis of Casts 5 (bottle number 3), 19 and 20 (all bottles) were considered suspect by the data originator. These samples were not used in the calibration data set. The offset between bottle salinity and CTD salinity was examined for each sensor to see if it varied with pressure or bottle salinity. Four data points were deemed to be outliers and removed from the analysis. No significant trends were observed for either sensor. Consequently, simple mean offsets, each based on 61 observations, were applied to the data (corrected salinity = raw salinity + mean offset). Details of both sensor calibrations are given in the table below, however, only the data from the primary sensors was kept in the series and the secondary channels were dropped.

Temperature

No further calibration was possible.

Pressure

There were no casts where the CTD pressure sensor was logging in air. No adjustments were made to the values resulting from application of manufacturer's coefficients during the initial processing.

Beam attenuation

Calibrated with air readings from the previous cruise (CD158).

Turbidity

No further calibration was possible.

Transmissometer 2

The data in this channel remained as raw voltages due to lack of calibration information and consequently were dropped from the series.

Dissolved oxygen

There were no samples against which to calibrate the sensor further.

Chlorophyll-a

There were no samples against which to calibrate the sensor further.

Screening

Reformatted CTD data were transferred onto a graphics workstation for visualisation using the in-house editor SERPLO. Downcasts and upcasts were differentiated and the limits manually flagged. No data values were edited or deleted. Flags were applied to suspect data values.

Banking

Once BODC quality control screening was complete, the CTD downcasts were binned to 1 db and banked in the BODC 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-McCave: Hydrographic and flow changes at sharp climate transitions along the northern edge of the Atlantic meridional overturning circulation, 0-16ka BP

This project was a component of the NERC Rapid Climate Change Programme under grant number NER/T/S/2002/00436. The project ran from April 2004 until January 2008.

Professor I. N. McCave from Cambridge University was the Principal Investigator. Co-Investigators on the project included Professor R. Rickaby, University of Oxford; Professor I. R. Hall, Cardiff University; Professor H. Elderfield, University of Cambridge.

The objectives of the project were to:

• Document changes in hydrographic structure and flow of water masses along the Scotland-Labrador boundary of the N. Atlantic through late Glacial and Holocene rapid climate changes.
• Examine leads and lags in water temperature, salinity, nutrient structure of the water column and flow speed to provide a key to assessing possible outcomes to changes in these parameters observable today.
• Estimate the changing flux of the outflow though Faeroe Bank Channel using palaeo-geostrophy.
• Calibrate Sortable Silt grainsize and AMSus flow speed proxies using surface sediments from long-term current meter sites in the region.

Target sites for this investigation were Faeroe Bank Channel, South Iceland Rise, and Eirik Drift.

Data sets from this project arose from a fieldwork campaign during a 4 week Charles Darwin cruise CD159, in July 2004. CTD casts, sediment cores and water samples for isotopic analysis were collected during the cruise.

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: