Metadata Report for BODC Series Reference Number 1228802

• 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 Quality document for D350 stainless steel CTD attenuation

Stainless Steel Frame CTD:

The instrument (CTG Alphatracka II, serial no. 161050), after calibration, displayed values below the physical limits of attenuation. Calibration investigations showed last calibration to have been on 03/05/2001, nine years before the intrument was recording for this cruise. This leads BODC to suspect that the calibration is not robust and therefore absolute data values should be used with extreme caution.

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.

Instrumentation on cruise D350

Stainless steel framed CTD unit and attached sensors

A Sea-Bird Electronics 911+ CTD system was used, composed by an SBE11+ deck unit (serial number 11P-24680-0587) and an SBE9+ underwater unit (serial number 09P-31240-0720), the latter of which had last been serviced on 23 October 2008. The attached sensors are listed in the table below:

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.

Originators Processing Document for D350 CTDs

Sampling strategy

Multiple CTD casts were performed at each of the nine stations visited during the D350 cruise in the North Atlantic (Irminger and Iceland Basins) from 26 April to 09 May 2010. Both titanium and stainless steel rosette CTD frames were used. Generally, stations commenced at night (typically between 23:00 and 03:00 GMT). The titanium CTD was fitted with trace metal clean Ocean Technology Equipment (OTE) sampling bottles with external springs.

Data processing

Data processing was performed using SeaBird's own CTD data processing software, SBEDataProcessing-Win32: v.7.2a. Raw CTD files (.DAT) were converted to binary (to include both up and down casts) files (.CNS). A second output file (.ROS) contained bottle firing information.

• The SeaSoft program ALIGNCTD was used to shift the oxygen sensor data relative to the pressure data by five seconds, compensating for lags in the sensor response time. The output was written over the input file.
• WILDEDIT was used to scan data, twice calculating the standard deviation of a set of numbers of scans, setting values outside a set number of standard deviations of the mean to bad data values. On this cruise, the scan range was set to 500, with two standard deviations on the first pass and 10 standard deviations on the second.
• The routine CELLTM removed the effects of thermal 'inertia' on the conductivity cells after WILDEDIT was used.
• The .CNV file was converted from binary into ASCII format so it could be read in Pstar format. The headers were checked at this stage before proceeding to UNIX data processing.
• UNIX processing: Two versions of all Pstar scripts were created, one for stainless steel and one for titanium frame CTD. The first script (ctds0 and ctdt0) converted the SeaBird processed ascii file to Pstar format, also setting the required header information. The latitiude and longitude of the CTD a the bottom were manually added to the header. The output files (ctd350nnn.24hz (stainless steel) or ctd350nnnT.24hz (titanium)) contained the data averaged to 24Hz. The second script (ctds1 andctdt1) operated on the .24hz files and used the PEXEC program pmdian to remove residual spikes from all of the variables. The data were then averaged into a 1hz file. Absent data values in the pressure data were inerpolated across. Salinity, potential temperature, sigma0 and sigma2 (referenced to 2000db) were calculated and finally a ten second averaged file was created. The output files were ctd350nnn.1hz and ctd350nnn.10s andctd350nnnT.1hz and ctd350nnnT.10s. The third script (ctds2 and ctdt2) carried out a head to tail crop of the .1hz file to select the appropriate data cycles for just the up and down casts of the CTD. Before this script was run, the files were examined to determine the data cycles for the shallowest depth of the CTD rosette after initial soaking at 10m, the greatest depth, and the last good point before the CTD is removed from the water. these values were the entered in ctd2. The data were then cut and the file ctd350nnn.ctu or ctd350nnnT.ctu created. Finally, the data were averaged into two db pressure bins, creating the files ctd350nnn.2db or ctd350nnnT.2db. The fourth script (fir and firt0) covnerted the .ros file into Pstar fomat. It then took the relevant data cycles from the .10s averaged file and passed into a new file fir350nnn containign the mean values of all the variables at the bottle firing locations. The final scripts (sanfir and samfirt) created a file (sam350nnn containing selected variables from fir350nnn and fir350nnnT so that the results from bottle sampling could be added.

For CTD samples, a spreadsheet of bottle salinities and the corresponding Niskin bottle from which they were taken (derived from the raw CTD log sheets) was created for each CTD cast. Data from the files were then incorporated into the same files using the Pstar scripts sal0 and passal.

• The effect of thermal 'inertia' on the conductivity cells was removed using the routine CELLTM. This routine must only be run after WILDEDIT or any other editing of bad data values. The routine uses the temperature variable to adjust the conductivity values and if spikes exist in the former they are amplified in the latter. The algorithm used is documented fully in the cruise report.

Field calibration:

Coefficient A = 1.00003351 (this calibrates the primary conductivity sensor). Coefficient B = 1.00018424 (this calibrates the secondary conductivity sensor)

These were calculated using the algorithm:
dt = t^i - t^i-7
ctm^i = -b*ctm^i-7 +

The mean residual for the primary conductivity sensor (bottle cond - CTD sensor cond) = 0.0000523 ± 0.000528
The mean residual for the secondary conductivity sensor (bottle cond - CTD sensor cond) = 7.20E-15 ± 0.001125 (i.e. very very small)

Once conductivity was calibrated, all derived variables were then recalculated (i.e. salinity, potential temperature, density and oxygen)

In addition the oxygen sensor was calibrated following a linear regression analysis between the bottle oxygen (samples taken from CTD rosette bottles) and sensor oxygen measurements. It was decided that in this case a simple solution was the most appropriate and calibrated oxygen (ml/l) = sensor oxygen (ml/l) * 1.014824 The mean residual was 0.0003 ± ;0.02 ml/l

Coefficient A = 1.00013540 (this calibrates the primary conductivity sensor. Coefficient B = 1.00004397 (this calibrates the secondary conductivity sensor)

The mean residual for the primary conductivity sensor (bottle conductivity - CTD sensor conductivity) = -9.30E-15 ± 0.00081
The mean residual for the secondary conductivity sensor (bottle conductivity - CTD sensor conductivity) = 6.11E-15 ± 0.0007

No oxygen samples were collected from the titanium frame due to concerns over contamination of the dissolved iron samples so a cross calibration of the sensor against the calibrated stainless steel frame sensor was undertaken using only those stations where both CTD systems were deployed. After a lot of trial and error it was decided that the best calibration was obtained with this equation

Calibrated oxygen = 0.9878 * Oxygen + 0.2876 (all as ml/l)

The mean residual (stainless frame - titanium frame) was -0.055 ± -0.0002 (ml/l)

All other oxygen variables (i.e. umol/l, umol/kg) are derived from this calibrated oxygen variable

Note this calibration was done using data deeper than 1000 dbar as the deep water oxygen concentrations were less likely to change between the dual CTD casts.

References

For more information, please read the cruise report. Pages 105 to 109 detail the CTD cruise report.

Processing of D350 CTD data by BODC

Data processing:

Data were processed and calibrations were applied by the originator at University of Southampton before being sent to BODC in .DAT file format with a total of 28 files, generated by 17 stainless steel framed CTD casts and 11 titanium framed CTD casts taken on the cruise.

Reformatting:

• The parameters and units included in the originator files (for both stainless steel and titanium frames) were: Datacycle (number), day (DOY), hour (HHMMSS), lat, lon, press (db), temp (degC), salin (psu), potemp (deg.c), sigma0 (kg^m-3), oxygen (ml^l-1), oxygen_x (umol^l-1), oxygen_c (umol^kg-1), fluor (ug^l-1), trans (%), atten (1^m-1), temp2 (degC), salin2 (psu), potemp2 (deg.c), sigma2 (kg^m-3).
• The .DAT files were reformatted to internal format using the BODC standard procedure. Not every parameter was transferred as BODC re-derive certain parameters and other parameters contained metadata or non-environmental data.
• For some parameters, data were provided from the CTD rosette and a vane-mounted CTD. These data were cross-checked to ensure there were no major differences. As such, the decision was made to to carry the CTD rosette data through, as these are physically co-located to the other rosette bottles and the samples themselves. These parameters are available upon request.
• The following parameters were chosen as the final dataset for banking at BODC for both stainless steel and titanium CTD frames:

References

• Benson, BB. and Krause, DK. Jr., 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr., 29(3), 620-632
• Fofonoff, NP. and Millard, RC. Jr., 1983. Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science No 44, 53pp.

Screening:

Quality control flags were automatically added to data outside the expected parameter-specific range during the reformatting process. All parameters in the reformatted files were then visualised and screened using the in house software Edserplo, and any suspect data points were assigned a quality control flag.

Project Information

Iron Biogeochemistry in the high latitude North Atlantic - Irminger Basin Iron Study (IBIS)

Funding

Funding was provided by NERC, in the form of four standard (full Economic Cost - fEC) grants with a total value of £528,607. The project was a study of the iron (Fe) biogeochemistry in the high latitude North Atlantic, with the results providing a better understanding of the role that nutrients like iron play in the growth of phytoplankton cells in the ocean. The gathered data were intended to help computer modellers to design improved climate models that would allow for better predictions of the extent of climate change over the next hundreds of years.

Project dates - 21 June 2007 to 08 November 2013.

Background

With the rise in carbon dioxide concentrations throughout the world, the importance of carbon-ingesting marine plants, such as phytoplankton is becoming more important. As phytoplankton take up atmospheric carbon dioxide, they are helping to reduce the atmospheric concentration. Recently it has been discovered that the phytoplankton in many of the world's oceans are lacking in iron. For example, in the Southern Ocean, phytoplankton cell growth is limited by very low iron concentrations. Thus, they do not remove as much carbon dioxide as they could. Recent studies have suggested that iron may even play a role in the phytoplankton growth in the high latitude North Atlantic, which was thought to be iron replete.

Objectives

The main objective of this project was to study the iron biogeochemistry of the high latitude North Atlantic, assess whether community productivity in parts of the high latitude North Atlantic was iron limited following the annual spring bloom, and to determine the factors which lead to this situation. This project studied whether iron was limiting phytoplankton growth in the study area, by undertaking two cruises and taking samples of water, sedimenting material, and atmospheric dust and rain. The project also directly investigated whether iron is limiting the growth of phytoplankton in water samples from the study area.

Participants

• University of Southampton, School of Ocean and Earth Science.
• University of Liverpool, Earth Surface Dynamics.
• University of Essex, Biological Sciences.
• University of East Anglia, Environmental Sciences.

• Prof. Eric Achterberg, University of Southampton, School of Ocean and Earth Science (Principal Investigator)
• Dr. Gary Fones, University of Portsmouth, School of Earth and Environmental Sciences
• Dr. Richard Sanders, National Oceanography Centre, Science and Technology
• Dr. Christopher Mark Moore, University of Southampton, School of Ocean and Earth Science
• Prof. Richard Geider University of Essex, Biological Sciences
• Prof. Tim Jickells, University of East Anglia, Environmental Sciences
• Prof. Ric Williams, University of Liverpool, Earth, Ocean and Ecological Sciences

Methodology

• Took samples of water, sediments, atmospheric dust and rain.
• Calculated the supply ratios of iron (Fe) to nitrogen (N), phosphorus (P) and carbon (C) to the surface oceans and in sedimenting material.
• Calculated the oceanic transfers of these elements using models.
• Assessed whether iron was limiting phytoplankton growth using both models and water samples analysis.

More information can be found within the Gateway to Research website.

Fieldwork

Two research cruises

• RRS Discovery D350 - 26 April 2010 to 09 May 2010. Departed from Govan, UK and arrived in Reykjavík, Iceland. Study area: North Atlantic Ocean - Irminger and Iceland Basins. Principal Scientist: Dr. Mark Moore, University of Southampton.
• RRS Discovery D354 - 10 July 2010 to 11 August 2010. Departed from Avonmouth, UK and arrived in Birkenhead, UK. Study area: North Atlantic Ocean - Iceland and Irminger Basins. Principal Scientist: Prof. Eric Achterberg, University of Southampton.

Instrumentation

• Stainless Steel CTD rosette
• Titanium CTD rosette
• VM ADCP 75 kHz
• VM ADCP 150 kHz
• Stand Alone Pump Systems (SAPS)
• PELAGRA - Neutrally Buoyant Sediment Traps
• Trace metal clean tow fish
• Seasoar with CTD, fluorometer and Laser Optical Plankton Counter (LOPC)
• Zooplankton nets
• Underway - Navigation, surface and meteorology

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: