Metadata Report for BODC Series Reference Number 1781732

• 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

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

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.

Benthos Programmable Sonar Altimeter (PSA) 916 and 916T

The PSA 916 is a submersible altimeter that uses the travel time of an acoustic signal to determine the distance of the instrument from a target surface. It provides the user with high resolution altitude or range data while simultaneously outputting data through a digital serial port. A wide beam angle provides for reliable and accurate range measurements under the most severe operational conditions. The instrument is electronically isolated to eliminate any potential signal interference with host instrument sensors. The PSA 916 is an upgrade of the PSA 900.

The standard model (PSA 916) has an operational depth range of 0 - 6000 m, while the titanium PSA 916T has a depth range of 0 - 10000 m. All other specifications for the two versions are the same.

Specifications

Further details can be found in the manufacturer's specification sheets for the PSA 916 and the PSA 916T.

Instrument Description

The Ultra Clean CTD system

The system consists of 3 major modules:

• A box-shaped titanium CTD frame with 24 sampling bottles made of PVDF and titanium
• A clean air container for contamination-free (sub)sampling
• A special deep sea winch with an iron-free Super Aramid CTD cable

Further details on the Ultra Clean CTD system can be found on page 25 of thecruise report

The system consists of a SBE9plus with a SBE5T pump and a SBE11plus V2 Deck Unit with the use of the following additional sensors:

For bottom-detection 2 devices were installed: a Benthos PSA-916 altimeter and a bottom switch with a weight on a 10 metre rope.

The Large Volume CTD system

The CTD system consists of a SBE9plus underwater unit with a a SBE5T underwater pump and a SBE11plus V2 deck unit, with the use of the following additional sensors:

For bottom detection two devices were installed: A Benthos PSA-916 altimeter and a bottom switch with a weight on a 10 metre rope. For further details on the CTD please see page 26 of thecruise report.

The Brine-system

The Brine CTD-system was designed to measure and sample in brines. Brines are a type of highly saline underwater lake like basins on the bottom of the Mediterranean Sea. The system consists of a SBE9plus underwater unit with a SBE5T underwater pump and a SBE11plus V2 deck unit ith the following sensors attached:

A bottom-switch with a weight on a 10 meter rope was used for bottom-detection. In this occasion a Benthos PSA-916 altimeter was mounted for extra bottom- detection and to find out whether it is possible to detect the seawater/brine-interface acoustically. For further details on the CTD please see page 27 of thecruise report.

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.

WETLabs C-Star transmissometer

This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.

Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.

This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.

Specifications

Further details are available in the manufacturer's specification sheet or user guide.

BODC Processing

Reformatting

The data arrived at BODC as 78 ASCII files (34 standard CTD casts, 43 trace metal CTD casts and 1 Brine system CTD cast). Data were reformatted to BODC internal QXF format. The following table shows how the variables within the ASCII files were mapped to the appropriate BODC parameter codes.

BODC assigned each CTD event with a unique identifier (OID) based on the originator's event log. OID was assembled from the originator's station, cast number and cast type i.e. 01_01_UCC (station_cast_cast type).

Definition of CAST TYPE:

• ROS - CTD with 25 dm3 bottle in rosette sampler
• UCC - CTD with 27 dm3 bottles in Ultra Clean frame
• BRN - CTD for Brine Sampling

Screening

Reformatted CTD data were visualised using the in-house graphical editor EDSERPLO. Quality control flags were applied to data as necessary.

Entirely null channels were removed from 3 files:

• BR370183 (series 1781523) - ATTNDR01, CPHLPS01 and DOXMZZXX channels
• UC370071 (series 1782016) - DOXMZZXX channel
• UC370341 (series 1782329) - CPHLPS01 channel

Originator's Data Processing

Sampling Strategy

During the cruise three different CTD-systems were deployed.

1. An Ultra Clean CTD-system for ultra clean trace metal sampling (43 casts)
2. A Large Volume CTD for almost all the other sampling like DIC and alkalinity, dissolved oxygen (DO) and phytoplankton (34 casts)
3. For one CTD-cast the so called Brine-system was deployed.

A total of 78 casts were carried out during the cruise.

The Ultra Clean CTD System

To avoid contamination, the frame of the Ultra Clean CTD (UCC) system was made of titanium and all the electronic pressure housings and other parts were made of titanium or clean plastics like Teflon, PVDF or POM. To prevent contamination and to keep the UCC safe and secure the UCC was at all times placed inside the clean air container (meeting class 100 clean-room specifications) when not in use during casts. Prior to a cast the frame was prepared inside that container and transported to the CTD-launching spot using a custom made aluminum pallet and a longbedded forklift. After the cast the UCC was immediately returned to the clean air container to avoid contamination of the equipment with grease, rust or smoke particles from the ship. After closing of the container the air treatment system starts to clean the air using HEPA-filters (meeting class 100 clean-room specifications after 15 minutes).

Data Processing

At the very beginning of the cruise a broken conductor in the termination of the cable caused some delay. The Dissolved oxygen sensor of the UCC system was unreliable in the first casts due to contact problems in the bulkhead connector of the CTD underwater unit. This problem was circumvented by slightly bending of the contact-pins and so enforcing better contact. At one occasion the Multivalve broke during transport of the UCC-frame out of the container. The repair took a couple of hours because spares appeared not to be fully compatible. For the future fully compatible spares will be brought. During the cruise strange RS-232/modem problems occurred sometimes. These problems are still not fully understood or diagnosed. The fluorometer of the UCC showed in the beginning of the cruise a greater sensitivity than the fluorometer of the 25L CTD. However during the cruise its noise-level increased and at the end of the cruise is was decided to exchange it for a spare and send the instrument back to Chelsea for repair, probably under warranty.

Field Calibrations

For the in situ calibration of the profiling CTD-thermometers (SBE-3) a Seabird reference thermometer (type SBE35) was used. A first analysis of the temperature calibration data showed that both profiling thermometers performed well within the specifications: the accuracy was better than 1 mK with a standard deviation of 0.8 mK. The CTD samples were analyzed on board for salinity using a Guildline 8400B Autosal, calibrated by a OSIL standard batch P154, and used to calibrate the UCC salinity. The first analysis of the salinity data showed that the conductivity-sensor of the UCC system performed within the specifications. The difference between the Autosal-salinity and the UCC salinity was on average smaller than 0.001 with a standard deviation of 0.0005. The conductivity sensor of the 25L CTD showed a small offset of 0.004 in salinity. During the postprocessing the data was corrected.

After most of the casts of the 25L CTD samples were tapped for Winkler titrations in order to calibrate the Dissolved Oxygen sensors. A first analysis of the Winkler results showed that the Dissolved Oxygen sensor drifted slowly and linear in time towards less sensitive. After correction for this drift the average difference between Winklers and Dissolved Oxygen sensor was 0.1 µM/kg with a standard deviation of 1.2 µM/kg

Further details on the originators processing can be found in the cruise report.

Project Information

GEOTRACES

Introduction

GEOTRACES is an international programme sponsored by SCOR which aims to improve our understanding of biogeochemical cycles and large-scale distribution of trace elements and their isotopes (TEIs) in the marine environment. The global field programme started in 2009 and will run for at least a decade. Before the official launch of GEOTRACES, fieldwork was carried out as part of the International Polar Year (IPY)(2007-2009) where 14 cruises were connected to GEOTRACES.

GEOTRACES is expected to become the largest programme to focus on the chemistry of the oceans and will improve our understanding of past, present and future distributions of TEIs and their relationships to important global processes.

This initiative was prompted by the increasing recognition that TEIs are playing a crucial role as regulators and recorders of important biogeochemical and physical processes that control the structure and productivity of marine ecosystems, the dispersion of contaminants in the marine environment, the level of greenhouse gases in the atmosphere, and global climate.

Scientific Objectives

GEOTRACES mission is: To identify processes and quantify fluxes that control the distribution of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions.

Three overriding goals support the GEOTRACES mission

• Determine ocean distributions of selected TEIs at all major ocean basins
• Evaluate the sources, sinks, and internal cycling of these TEIs and thereby characterize more completely their global biogeochemical cycles
• Provide a baseline distribution in the Polar Regions as reference for assessing past and future changes.

These goals will be pursued through complementary research strategies, including observations, experiments and modelling.

Fieldwork

The central component of GEOTRACES fieldwork will be a series of cruises spanning all Ocean basins see map below.

Three types of cruise are required to meet the goals set out by GEOTRACES. These are

• Section cruises - These will measure all the key parameters (see below) over the full depth of the water column. The sections were discussed and approved by the International GEOTRACES Scientific Steering Committee at the basin workshops.
• Process Studies - These will investigate a particular process relevant to the cycling of trace metal and isotopes. They must follow the "Criteria for Establishing GEOTRACES Process Studies" and be approved by the International GEOTRACES Scientific Steering Committee.
• Cruises collecting GEOTRACES compliant data - These will collect some trace element or isotope data. They must follow the GEOTRACES Intercalibration and Data Management protocols

IPY-GEOTRACES

The IPY-GEOTRACES programme comprised of 14 research cruises on ships from 7 nations; Australia, Canada, France, Germany, New Zealand, Japan and Russia. The cruises will not be classified in the same way as the full GEOTRACES programme since the intercalibration protocols and data management protocols had not been established before the start of the IPY. But IPY-GEOTRACES data will still be quality controlled by GDAC and in the majority of cases verified versus Intercalibration standards or protocols.

Key parameters

The key parameters as set out by the GEOTRACES science plan are as follows: Fe, Al, Zn, Mn, Cd, Cu; 15N, 13C; 230Th, 231Pa; Pb isotopes, Nd isotopes; stored sample, particles, aerosols.

Weblink:

http://www.bodc.ac.uk/geotraces/
http://www.geotraces.org/

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: