Metadata Report for BODC Series Reference Number 1118321

• 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

RRS Discovery D344 Navigation Quality Control Report

Position

Position channels look good. There was a gap at the end of the dataset but this got trimmed off at the end of processing. Flags were automatically applied to this also.

Heading

Heading channel looks good. Data are within the permitted maximum and minimum parameter values and there are some parts of the datasets where absent value range have been recorded. These absent values were automatically flagged.

Speed and course over ground

Both the speed over ground and course over ground data look good. Both channels exhibit a small amount of null values and unrealistic data values.These were flagged accordingly.

Bathymetry

The single-beam is of moderate quality with only approximately 40% of the data flagged. It contains some noisy patches and an abundance of very short dropouts and two extended drop-outs. Despite this, the single-beam data compares well with GEBCO. The noisy patches and drop outs have been flagged accordingly. There are also some absent values recorded at the beginning and the end of the channel that have been flagged.

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

Kongsberg Simrad EA500 bathymetric echosounder

The EA500 is a bathymetric echosounder that can be used in water as deep as 10,000 m. It features triple frequency operation with a separate digitiser for each channel and high transmitted power with an instantaneous dynamic range of 160 dB. The instrument can operate with several pulses in the water simultaneously and has bottom tracking capabilities. A wide range of transducers (single beam, split beam or side-looking) is available and the ping rate is adjustable up to 10 pings per second. The split beam operation measures the athwartships inclination angle of the seabed.

This instrument was introduced in June 1989 and and replaced by the EA 600 in 2000.

Specifications

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

RRS Discovery D344 Navigation Instrumentation

Navigation and bathymetry

There are four GPS receivers on RRS Discovery: the Trimble 4000, which is a differential GPS; the Glonass, which uses a combination of Russian and American satellite networks; the Ashtech; and the SeaStar G12.

Two sources of bathymetric data were available on this cruise; a Precision Echosounding (PES) hull mounted fish transducer; and a Simrad EA500 hydrographic echosounder.

Trimble 4000DS Global Positioning System receiver

The Trimble 4000DS Differential Surveyor is similar to the 4000RS (a Maxwell-based receiver that is oriented toward precision positioning applications. It is intended for use as a DGPS base station, generating RTCM-104 corrections). The 4000Ds can apply RTCM-104 corrections to the satellite data it receives in order to generate accurate position fixes in real time.

RRS Discovery D344 Navigation Data Processing Procedures

Navigation processing

Originator's processing

Data were taken from the ship's TECHSAS streams and formatted into MSTAR netCDF format. All times were defined as seconds from 00:00:00 01/01/2009. Depths from the echosounder were visualised and bad data replaced with NaNs. A Carter correction was then applied.

Data were removed that were not in the correct chronological order. Data from the Ashtech GPS is used to correct the heading given by the gyro compass. The differences are calculated and then cleaned to produce a correction. This is then applied to the heading from the gyro compass.

Files delivered to BODC

BODC processing

Data were banked at BODC following standard banking procedures. Data were averaged to 60 second intervals. All navigational and bathymetric data were transferred from MSTAR format into BODC internal format (a NetCDF subset).

The originator's variables were mapped to appropriate BODC parameter codes as follows:

met_light_di344_cal_01.nc

wind_di344_01.nc

sim_di344_d***_nav.nc

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

Position

A check was run on positional data to identify gaps and improbable values (through the calculation of speed). Improbable speeds were found where the latitude and longitude data had unrealistic values. Some improbable speeds occurred where the latitude and longitude had been constant for a while preceding the high speed. On inspection, it appeared that the GPS data were sticking at constant values and then suddenly jump back to being correct. The periods of constant latitude and longitude were flagged null and, along with any gaps, linearly interpolated over.

Distance Run

Distance run was recalculated using the clean latitude and longitude at BODC.

GEBCO

Bathymetric depth from the GEBCO Centenary 1-Minute Global Grid was merged into the file as a supplementary source of bathymetry for comparison purposes.

Bathymetry

Bathymetry data were screened independently as well as against GEBCO bathymetry measurements. The Simrad EA500 echo-sounder compares well and follows GEBCO's trend.

References

Cunningham, S.A., Wright, P. (ed.), 2010. RRS Discovery Cruise D344, 21 Oct-18 Nov 2009. RAPID Mooring cruise report. Southampton, UK, National Oceanography Centre, Southampton, 225pp. (National Oceanography Centre Southampton Cruise Report, 51)

Project Information

Monitoring the Meridional Overturning Circulation at 26.5N (RAPIDMOC)

Scientific Rationale

There is a northward transport of heat throughout the Atlantic, reaching a maximum of 1.3PW (25% of the global heat flux) around 24.5°N. The heat transport is a balance of the northward flux of a warm Gulf Stream, and a southward flux of cooler thermocline and cold North Atlantic Deep Water that is known as the meridional overturning circulation (MOC). As a consequence of the MOC northwest Europe enjoys a mild climate for its latitude: however abrupt rearrangement of the Atlantic Circulation has been shown in climate models and in palaeoclimate records to be responsible for a cooling of European climate of between 5-10°C. A principal objective of the RAPID programme is the development of a pre-operational prototype system that will continuously observe the strength and structure of the MOC. An initiative has been formed to fulfill this objective and consists of three interlinked projects:

• A mooring array spanning the Atlantic at 26.5°N to measure the southward branch of the MOC (Hirschi et al., 2003 and Baehr et al., 2004).
• Additional moorings deployed in the western boundary along 26.5°N (by Prof. Bill Johns, University of Miami) to resolve transport in the Deep Western Boundary Current (Bryden et al., 2005). These moorings allow surface-to-bottom density profiles along the western boundary, Mid-Atlantic Ridge, and eastern boundary to be observed. As a result, the transatlantic pressure gradient can be continuously measured.
• Monitoring of the northward branch of the MOC using submarine telephone cables in the Florida Straits (Baringer et al., 2001) led by Dr Molly Baringer (NOAA/AOML/PHOD).

The entire monitoring array system created by the three projects will be recovered and redeployed annually until 2008 under RAPID funding. From 2008 until 2014 the array will continue to be serviced annually under RAPID-WATCH funding.

The array will be focussed on three regions, the Eastern Boundary (EB), the Mid Atlantic Ridge (MAR) and the Western Boundary (WB). The geographical extent of these regions are as follows:

• Eastern Boundary (EB) array defined as a box with the south-east corner at 23.5°N, 25.5°W and the north-west corner at 29.0°N, 12.0°W
• Mid Atlantic Ridge (MAR) array defined as a box with the south-east corner at 23.0°N, 52.1°W and the north-west corner at 26.5°N, 40.0°W
• Western Boundary (WB) array defined as a box with the south-east corner at 26.0°N, 77.5°W and the north-west corner at 27.5°N, 69.5°W

References

Baehr, J., Hirschi, J., Beismann, J.O. and Marotzke, J. (2004) Monitoring the meridional overturning circulation in the North Atlantic: A model-based array design study. Journal of Marine Research, Volume 62, No 3, pp 283-312.

Baringer, M.O'N. and Larsen, J.C. (2001) Sixteen years of Florida Current transport at 27N Geophysical Research Letters, Volume 28, No 16, pp3179-3182

Bryden, H.L., Johns, W.E. and Saunders, P.M. (2005) Deep Western Boundary Current East of Abaco: Mean structure and transport. Journal of Marine Research, Volume 63, No 1, pp 35-57.

Hirschi, J., Baehr, J., Marotzke J., Stark J., Cunningham S.A. and Beismann J.O. (2003) A monitoring design for the Atlantic meridional overturning circulation. Geophysical Research Letters, Volume 30, No 7, article number 1413 (DOI 10.1029/2002GL016776)

RAPID- Will the Atlantic Thermohaline Circulation Halt? (RAPID-WATCH)

RAPID-WATCH (2007-2014) is a continuation programme of the Natural Environment Research Council's (NERC) Rapid Climate Change (RAPID) programme. It aims to deliver a robust and scientifically credible assessment of the risk to the climate of UK and Europe arising from a rapid change in the Atlantic Meridional Overturning Circulation (MOC). The programme will also assess the need for a long-term observing system that could detect major MOC changes, narrow uncertainty in projections of future change, and possibly be the start of an 'early warning' prediction system.

The effort to design a system to continuously monitor the strength and structure of the North Atlantic MOC is being matched by comparative funding from the US National Science Foundation (NSF) for the existing collaborations started during RAPID for the observational arrays.

Scientific Objectives

• To deliver a decade-long time series (2004-2014) of calibrated and quality-controlled measurements of the Atlantic MOC from the RAPID-WATCH arrays.
• To exploit the data from the RAPID-WATCH arrays and elsewhere to determine and interpret recent changes in the Atlantic MOC, assess the risk of rapid climate change, and investigate the potential for predictions of the MOC and its impacts on climate.

This work will be carried out in collaboration with the Hadley Centre in the UK and through international partnerships.

Mooring Arrays

The RAPID-WATCH arrays are the existing 26°N MOC observing system array (RAPIDMOC) and the WAVE array that monitors the Deep Western Boundary Current. The data from these arrays will work towards meeting the first scientific objective.

The RAPIDMOC array consists of moorings focused in three geographical regions (sub-arrays) along 26.5° N: Eastern Boundary, Mid-Atlantic Ridge and Western Boundary. The Western Boundary sub-array has moorings managed by both the UK and US scientists. The other sub-arrays are solely led by the UK scientists. The lead PI is Dr Stuart Cunningham of the National Oceanography Centre, Southampton, UK.

The WAVE array consists of one line of moorings off Halifax, Nova Scotia. The line will be serviced in partnership with the Bedford Institute of Oceanography (BIO), Halifax, Canada. The lead PI is Dr Chris Hughes of the Proudman Oceanographic Laboratory, Liverpool, UK.

All arrays will be serviced (recovered and redeployed) either on an annual or biennial basis using Research Vessels from the UK, US and Canada.

Modelling Projects

The second scientific objective will be addressed through numerical modelling studies designed to answer four questions:

• How can we exploit data from the RAPID-WATCH arrays to obtain estimates of the MOC and related variables?
• What do the observations from the RAPID-WATCH arrays and other sources tell us about the nature and causes of recent changes in the Atlantic Ocean?
• What are the implications of RAPID-WATCH array data and other recent observations for estimates of the risk due to rapid change in the MOC?
• Could we use RAPID-WATCH and other observations to help predict future changes in the MOC and climate?

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: