Metadata Report for BODC Series Reference Number 1719700

• 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 SBE 37-SMP MicroCAT

The SBE 37-SMP MicroCAT is a high accuracy conductivity and temperature recorder (pressure optional) with Serial interface, internal battery, non-volatile FLASH Memory and integral Pump. The Integral Pump runs for 1 second each time the MicroCAT samples, improving the conductivity response and giving improved anti-foul protection.

Designed for moorings and other long-duration, fixed-site deployments, MicroCATs have non-corroding titanium housings rated for operation to 7000 meters or pressure sensor full scale-range. Communication with the MicroCAT is over an internal, 3-wire, RS-232C link. The MicroCAT's aged and pressure-protected thermistor has a long history of exceptional accuracy and stability (typical drift is less than 0.002°C per year). Electrical isolation of the conductivity electronics eliminates any possibility of ground-loop noise.

Specifications

Further information can be found via the following link: Sea-Bird SBE 37-SMP MicroCAT Datasheet

DIMES Calibration Coefficients

Processing log

DIMES Sea-Bird MicroCAT data processing document

This document outlines the procedures undertaken to process and quality assure the MicroCAT data collected under the DIMES project. These procedures follow those of the RAPIDMOC and MOCHA projects, which are outlined below.

Originator's processing

The raw data are downloaded from the instrument and converted to ASCII format. All processing is performed in Matlab.

Calculating calibration coefficients

Prior to deployment and on recovery, a CTD dip is performed with the MicroCATs strapped onto the CTD frame. This allows calibration of the MicroCAT data by comparing the MicroCAT data with the CTD data. As the MicroCATs adjustment is much slower than the CTD, data are only compared during bottle stops and after the sensors have adjusted. Bottle stops on these calibration dips last no less than 5 minutes.

Any discrepancy between the MicroCAT clock and the CTD clock is calculated and corrected if necessary.

An average offset (MicroCAT - CTD) is calculated for temperature, conductivity and pressure during the stable period of each bottle stop and interpolated onto the instrument deployment depths. For temperature and conductivity, an average of the offsets derived during the bottle stops is calculated for a specified pressure range where the data are stable (deep water). For pressure, the average offset interpolated to the deployment depth is used. If the calibration dip is shallower than the deployment depth, the offset is extrapolated to the deployment depth.

All the offsets are visually checked and adjusted if necessary. For temperature, if the calculated offsets are less than 0.003 in magnitude no offset is applied i.e. the offsets are adjusted to 0.000.

Applying calibrations

The data are calibrated using the pre and post deployment calibration coefficients. The calibration can be applied as either

• A linear trend between the pre and post deployment coefficients
• A constant offset using the pre deployment coefficient
• A constant offset using the post deployment coefficient
• A constant offset using an average of the pre and post deployment coefficients
• A general linear trend using either the pre or post deployment coefficient

If required, a conductivity pressure correction can be applied. This is used if the pressure channel shows spurious data in a particular time interval. A drift in the pressure data can also be removed.

To aid the quality of the calibration, data from CTD casts performed near mooring locations on previous cruises are used as a reference and are visually compared with the MicroCAT data.

Quality control

All variables in specified time intervals can be set to dummy values if the data are suspect and it is also possible to apply an offset to a subsection of a particular channel, if required. Interactive despiking can be carried out on the temperature and conductivity data, if present, by selecting data based on a T-S plot. Automatic despiking can also be performed using the option to exclude data outside the 6σ area.

The last stage of the processing is to grid the data onto a pressure field and visually check against historical data. This enables the calibrations to be checked and adjusted if necessary. On occasion, comparison of the time series with historical data and series from nearby instruments highlights the need for removal of a drift from one or more data channels. This is accomplished by removing a linear trend from the appropriate channel(s) and may affect the entire series or a subsection thereof. If a trend has been removed it will be noted in the 'DIMES Calibration Coefficients' section of the documentation.

BODC processing

Data are received after quality checks have been made and calibrations have been applied. The data files are submitted in ASCII format as one file per instrument.

Once the submitted data files are safely archived, the data undergo reformatting and banking procedures:

• The data files are transferred into a common format, a NetCDF subset.

• Standard parameter codes are assigned that accurately describe the data (see Parameter mapping section below).

• Unit conversions are applied, if necessary, so that units are standardised (see Parameter mapping section below).

• Salinity is derived using UNESCO 1983 polynomial.

• The data are screened visually and any spikes or instrument malfunctions can be clearly labelled with quality control flags.

• Comprehensive documentation is prepared describing the collection, processing and quality of each data series.

• Detailed metadata and documents are loaded to the database and linked to each series so that the information is readily available to future users.

Parameter mapping

The following describes the parameters contained in the originator's files and their mapping to BODC parameter codes:

Parameter derivation

The following describes the parameters derived by BODC and their mapping to BODC parameter codes:

Project Information

Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) project document

DIMES is a US/UK field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models are highly sensitive to the representation of mixing processes in the southern limb of the MOC, within the Southern Ocean, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. Theories and models of the Southern Ocean circulation have been built on the premise of adiabatic flow in the ocean interior, with diabatic processes confined to the upper-ocean mixed layer. Interior diapycnal mixing has often been assumed to be small, but a few recent studies have suggested that diapycnal mixing might be large in some locations, particularly over rough bathymetry. Depending on its extent, this interior diapycnal mixing could significantly affect the overall energetics and property balances for the Southern Ocean and in turn for the global ocean. The goals of DIMES are to obtain measurements that will help us quantify both along-isopycnal eddy-driven mixing and cross-isopycnal interior mixing.

DIMES includes tracer release, isopycnal following RAFOS floats, microstructure measurements, shearmeter floats, EM-APEX floats, a mooring array in Drake Passage, hydrographic observations, inverse modeling, and analysis of altimetry and numerical model output.

DIMES is sponsored by the National Science Foundation (U.S.), Natural Environment Research Council (U.K) and British Antarctic Survey (U.K.)

For more information please see the official project website at DIMES

Data Activity or Cruise Information

Data Activity

DIMES Moored Instrument Rig NW_1_201012

This rig was deployed as part of the mooring array of the DIMES (Diapycnal and isopycnal mixing experiment in the Southern Ocean) project.

The rig was anchored by a 1970 kg dead weight and kept erect with groups of glass spheres and floats distributed along the mooring.

Instruments deployed on the rig

Related Data Activity activities are detailed in Appendix 1

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Drake Passage

The World Ocean Circulation Experiment (WOCE, 1990-1998) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

The Drake Passage is the narrowest constriction of the Antarctic Circumpolar Current (ACC) - the largest current in the world and connects all three major oceanic basins both horizontally and vertically, thus being a key control in the global overturning circulation.Within the Drake Passage, two repeat hydrographic sections (SR1 and SR1b) were established by WOCE. These were designed to extend measurements collected earlier by the International Southern Ocean Studies (ISOS) programme and have continued beyond the WOCE time-frame.

The original section was SR1 (which also covers part of the A21 one time survey track). Subsequently, the section was shifted to the east (and designated SR1b) in order for it to lie on a satellite ground track as illustrated in the image below.

In addition to the hydrographic measurements, UK research in Drake Passage also includes a network of coastal and deep tide gauges, analysis of satellite altimeter data, and state-of-the-art global numerical modeling.

Related Fixed Station activities are detailed in Appendix 2

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:

Appendix 1: NW_1_2010

Related series for this Data Activity are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.

Appendix 2: Drake Passage

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.