Metadata Report for BODC Series Reference Number 1108836

• 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

Quality report

One of the beams of the LADCP broke suddenly after station 14, and was detected after station 20 during the originator's processing of the data. Although only three beams are necessary to calculate the three velocity components these tend to be less reliable. Therefore please note, that data from stations 14-20 are likely to be less reliable than the data from stations 2-13.

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

Instrument Description

The LADCP data were collected using the instrumentation detailed below:

The LADCP was configured to have a standard 10 x 16 m bins, with one water track and one bottom track ping in a two second ensemble, and a 5 m blank at the surface. Data were collected in beam coordinates and rotated to earth coordinates during post-processing. The instruments were mounted in a downward-looking orientation and positioned near the centre of a Sea-Bird 9 11 plus CTD frame.

One of the beams of the first LADCP broke suddenly after station 14, and was detected after station 20 during the processing of the data. The LADCP was then replaced after station 20. However, after station 20 there was a problem with a hardware bug which meant that heading was not being recorded. Therefore, only data before cast 20 have been provided.

Teledyne RDI's Workhorse Long Ranger ADCP

The Workhorse Long-Ranger acoustic doppler current profiler (Teledyne RD Instruments) is a long-range and long-term self contained ADCP. It has a patented broadband signal (75 kHz) and a standard depth rating of 1500m. It operates effectively between temperatures of -5°C and 45°C and has a velocity accuracy of ±1% ±5mm/s.

The instrument comprises:

• An aluminium transducer head with four beams at 20^o from the vertical in a convex configuration, temperature sensor, electronic assemblies, fluxgate compass, pitch and roll sensors
• 4 x 28 D-cell alkaline battery packs
• 40 MB PC card internal memory (upgradeable to 440 MB)
• 1500m depth rated 6061 aluminium pressure case. End cap with wet material connector and dummy plug

BODC Processing

The data were received in matlab format and converted into BODC internal format. Only u_nodetide and v_nodetide were retained in the QXF format, as u_bot and v_bot are processing steps used to correct u_nodetide and v_nodetide, whilst u_detide and v_detide have undergone subjective processing procedures. The following table shows how the variables within the matlab files were mapped to appropriate BODC parameter codes:

All reformatted data were visualised using the in-house Edserplo software. Suspect and missing data were marked by adding an appropriate quality control flag.

Note that u_bot and v_bot bottom track data are available on request.

Originator's Data Processing

Sampling Strategy

A total of 98 LADCPs were deployed, however only 18 LADCPs proved unproblematic. Station 1 was a test station which comprised of one downward-looking and one upward-looking LADCP deployed simultaneously. However, given the number of stations scheduled and the tendency of LADCPs to fail rather quickly, the originators decided to use only a downward-looking instrument for the rest of the cruise. Data from the test station was not provided. Station 5 was aborted as the CTD was giving bad data and the station was repeated shortly after (named station 6).

Prior to each station the ADCP was connected to a laptop in the deck lab for pre-deployment tests and the instrument was programmed. After each station the instrument was reconnected to the laptop for the retrieval of the data. The battery package was charged between stations. The raw data for each station were downloaded from the instrument and copied into a central data directory.

Processing

Processing was carried out using LDEO LADCP processing software version 7b (Visbeck, 2002) and was used to; correct for sound speed using the CTD calibrated data, calculate the barotropic velocity from the ship position at the beginning and end of the cast, and exclude bad quality data (large tilt of the CTD package, low backscatter etc). Please refer to Visbeck (2002) for further processing details.

References

Visbeck, M., 2002. Deep velocity profiling using Lowered Acoustic Doppler Current Profilers: Bottom track and inverse solutions. Journal of Atmospheric Oceanic Technology, 19, 794?807.

Project Information

Antarctic Deep Water Rates of Export (ANDREX) project document

ANDREX is a UK field programme aimed at investigating the role of the Weddell Gyre in the Meridional Overturning Circulation (MOC) and its influence on deep ocean properties.

The MOC is a critical regulator of Earth's climate and is crucial for deep water ventilation across the globe. Surface currents transport waters towards the poles, where they become dense and sink, flowing equatorward as deep, cool currents. The MOC ensures that the deep oceans remain ventilated and conducive to life, and is also important for anthropogenic carbon sequestration. The southern closure of the MOC in the Weddell Sea is strongly influenced by the Weddell Gyre, which facilitates the exchange of waters between the Antarctic Circumpolar Current (ACC) and the waters of the continental shelf. Cooling and sea ice formation in the Weddell Sea lead to overturning of the water column and the ventilation of Antarctic Bottom Water (AABW), which flows out of the Weddell Sea and into the deep oceans to the north. Thus, the Weddell Gyre plays an important role in the properties of deep ocean waters on a global scale.

The goals of ANDREX are to investigate the exchange of water masses between the ACC and the Weddell Sea, including AABW formation and ventilation rates, carbon and nutrient cycling, the influence of fresh water input from sea ice, precipitation and glacial melt, and the role of the Weddell Gyre in anthropogenic carbon sequestration. The project includes hydrographic, ventilation tracer, biogeochemical and bathymetric measurements along the outer rim of the Weddell Gyre.

ANDREX is funded by the UK Natural Environment Research Council (NERC) Antarctic Funding Initiative (AFI) and involves scientists from the National Oceanography Centre, Southampton (NOC), the British Antarctic Survey (BAS), the University of East Anglia (UEA), the University of Manchester, the Alfred Wegener Institut (AWI) and the Woods Hole Oceanographic Institution (WHOI).

For more information please see the official project website at ANDREX

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: