Metadata Report for BODC Series Reference Number 807923

• 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 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.

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

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

Underwater PAR radiometer

Underwater PAR radiometer of unknown type. Assumed to have a spectral response of 400-700nm. Could have any type of collector (flat plate cosine collector, spherical or hemispherical).

SeaTech Transmissometer

Introduction

The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.

Specifications

• Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
• Beam diameter: 15 mm
• Transmitted beam collimation: <3 milliradians
• Receiver acceptance angle (in water): <18 milliradians
• Light source wavelength: usually (but not exclusively) 660 nm (red light)

Notes

The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

Further details can be found in the manufacturer's Manual.

RV Pelagia 136 CTD Data Documentation

Cruise Principal Scientist and Data Originator

Dr. Hans van Haren, Nederlands Instituut voor Onderzoek der Zee (NIOZ), Texel, The Netherlands.

Content of data series

Instrumentation and data processing by originator

CTD unit and auxiliary sensors

Sea-Bird Electronics 911 Plus system fitted with the following additional sensors: 25 cm pathlength transmissometer (SeaTech SN160), Aquatracka III fluorometer (Chelsea Instrument SN028) and PAR sensor (K-meter SN4410) for downwelling irradiance.

Changes of sensors during the cruise:

Data were logged on a PC running Seabird Seasave data acquisition software v. 4.224 and manufacturer's calibration coefficients were applied to the raw data.

Data were supplied to BODC as individual Seabird ASCII files for each CTD cast with downcast and upcast in separate files. The profiles were binned to 0.5 db. Bottle files created by the Seabird software for each CTD-rosette sampling cast were also provided.

Sampling device

Rosette sampling system equipped with 24 x 12L NOEX sampling bottles. The pressure sensor was located close to the base of the bottles, at a distance of 1m from the top aperture of the bottles. The calculation of bottle sampling depth by BODC takes into account the geometry of the CTD frame.

No reversible thermometer was used.

BODC post-cruise processing and screening

Reformatting

The data were converted into BODC internal format (PXF) to allow use of in-house software tools notably the workstation graphics editor SERPLO. In addition to reformatting, the transfer program applied a conversion to transmissometer readings from percent transmission to attenuance using the algorithm:

where PL is the transmissometer pathlength in m (0.25 m).

Screening

Reformatted CTD data were transferred onto a high-speed graphics workstation. Downcast channels were screened graphically using custom in-house graphics editors. If present, spikes and suspicious values were manually flagged. No data values were edited or deleted; flagging was achieved by modification of the associated quality control flag to 'M' for suspicious values and 'N' for null.

Banking

Once screened on the workstation, the CTD downcasts were loaded into a database under the ORACLE Relational Database Management System.

Calibration

• Fluorescence: chlorophyll fluorescence (µg Chl a l^-1) was calibrated against extracted chlorophyll concentrations measured on samples collected during the cruise using the following equation determined by K. Wild-Allen (Napier University, Edinburgh, UK):

The calibration was based on the chlorophyll concentration of samples filtered through GF/F filters, extracted in 90% acetone and determined by spectrophotometry using the trichromatic method. 'Fluor' is the chlorophyll concentration (µg l^-1) from the CTD fluorometer output based on the manufacturer's calibration coefficients and measured at the time of the water sample collection (on the upcast).

Comparison of the chlorophyll concentration values from the CTD fluorometer in the upper 5 m with calibrated values from the underway fluorometer suggested that the CTD calibration overestimated the chlorophyll concentration in the surface layer. Based on average chlorophyll concentrations in upper 5 m from 16 CTD casts for which variability was small in the upper 5 m (SD<0.5 µg l^-1) the difference between the two fluorometers averaged 2.17 ±0.66 µg l^-1 (median=2.19 µg l^-1).

• Total suspended particulate matter concentration (TSED) was estimated at the University of Wales, Bangor, by linear regression of the concentration of total suspended particulate matter as measured on water samples by gravimetry and attenuance (ATTN) as measured by the CTD transmissometer at the time of sample collection (on the upcast). The resulting calibration equation is:

• Data from the other channels had already been calibrated by the data originator and no further calibration/correction was applied.

Comments on data quality

• Severe fouling of the tubing and electronic leads of the CTD unit resulted in its malfunctioning during the cruise. Although problems were noted early during the cruise, the cause of the malfunctioning was only discovered and solved more than half way through the cruise. Of all the channels, salinity appears to be the most affected. From casts 001 to 097, the upper 5 to 10 m of most salinity profiles had to be flagged as suspect. Salinity profiles from casts 013 to 017 were particularly bad and were almost entirely flagged as suspect. Judging the quality of the salinity data (and of the other parameter channels) is particularly difficult considering that a large amount of inherent hydrographic variability may be expected at this southern North Sea site. As a result flagging was kept to a minimum and users are advised to use data from casts 001 to 097 with caution. From casts 098 to 133, the CTD unit seems to have functioned well.
• Casts CTD062 and CTD083 were not loaded into Oracle (files contained less than 2 records).

Project Information

PROcesses of Vertical Exchange in Shelf Seas (PROVESS)

Introduction

PROVESS was an interdisciplinary study of the vertical fluxes of properties through the water column and the surface and bottom boundary layers. The project was funded by the European Community MAST-III programme (MAS3-CT97- 0159) and ran from March 1998 to May 2001.

Scientific Rationale

PROVESS was based on the integration of experimental, theoretical and modelling studies with the aim of improving understanding and quantification of vertical exchange processes in the water column, in particular in the surface and benthic boundary layers and across the> pycnocline. PROVESS also explored mechanisms of physical-biological coupling in which vertical exchanges and turbulence significantly affect the environmental conditions experienced by the biota with particular reference to aggregation, flocculation, sedimentation and trophic interactions.

Fieldwork

The experimental phase of the project was carried out at two contrasting sites in the North Sea: the northern North Sea site (NNS) and the southern North Sea site (SNS).

The two sites had the following characteristics:

At both locations measurements were concentrated at a central position with additional measurements being made to estimate horizontal gradients. Moored instruments (including current meters, temperature and pressure sensors, fluorometers, transmissometers, nutrient analysers and meteorological sensors) were deployed between 7 September and 5 November 1998 at the NNS and between 29 March and 25 May 1999 at the SNS. Each experiment was supported by intensive measurement series made from oceanographic ships and involving turbulence dissipation profiler CTD, particle size profilers, optical profilers, benthic sampling and water bottle sampling.

Details of the cruises were as follows:

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: