Metadata Report for BODC Series Reference Number 2058436

• 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 James Cook cruise JC187 navigation quality control report

Bathymetry

The single beam bathymetry channel provided more coverage, however the data were very noisy, and a large portion of the cruise would have required flagging. It was therefore decided to use the multibeam bathymetry channel (MBANSWCB), which was of much better quality, despite providing less coverage. Flags were however required for at least 10% of the channel due to noise and drop outs.

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 EM122 12kHz Multibeam Echosounder

The EM122 is designed to perform seabed mapping to full ocean depth with a high resolution, coverage and accuracy. Beam focusing is applied both during reception and transmission. The system has up to 288 beams/432 soundings per swath with pointing angles, which are automatically adjusted according to achievable coverage or operator defined limits.

This model uses both Continuous Wave and Frequency Modulated sweep pulses with pulse compression on reception, in order to increase the maximum useful swath width. The transmit fan is split in several individual sectors, with independent active steering, in order to compensate for the vessel movements.

In multiplying mode, two swaths per ping cycle are generated, with up to 864 soundings. The beam spacing is equidistant or equiangular and the transmit fan is duplicated and transmitted with a small difference in along track tilt, which takes into account depth coverage and vessel speed, to give a constant sounding separation along track. In high density mode, more than one sounding per beam can be produced, such that horizontal resolution is increased and is almost constant over the whole swath.

The EM122 transducers are modular linear arrays in a Mills cross configuration with separate units for transmit and receive. If used to deliver sub-bottom profiling capabilities with a very narrow beamwidth, this system is known as SBP120 Sub-Bottom Profiler.

The specification sheet can be accessed here Kongsberg EM122.

Specifications

EM122 versions

RRS James Cook cruise JC187 navigation instrumentation

Instrumentation

The EA640 singlebeam echo sounder was run throughout the cruise apart from during release and ranging of moorings. Both the 10 and 12 kHz were run in active mode triggered free running. Pulse parameters were altered during the cruise in response to changing depth. It was used with a constant sound velocity of 1500 ms^-1 throughout the water column to allow it to be corrected for sound velocity in post processing.

The EM122 multibeam echo sounder was run throughout the cruise in triggered free running mode, apart from during release and ranging of moorings. The position and attitude data were supplied from the Seapath 330+ due to its superior real-time heave. CTD and sound velocity profiler sensors were lowered from the vessel, to calibrate the bathymetric surveys.

Trimble Applanix Position and Orientation Systems for Marine Vessels (POSMV)

The Position and Orientation Systems for Marine Vessels (POSMV) is a real time kinematic (RTK) and differential global positioning system (DGPS) receiver for marine navigation. It includes an inertial system that provides platform attitude information. The instrument provides accurate location, heading, velocity, attitude, heave, acceleration and angular rate measurements.

There are three models of Applanix POSMV, the POS MV 320, POS MV Elite and the POS MV WaveMaster. POS MV 320 and POS MV WaveMaster are designed for use with multibeam sonar systems, enabling adherence to IHO (International Hydrographic Survey) standards on sonar swath widths of greater than ± 75 degrees under all dynamic conditions. The POS MV Elite offers true heading accuracy without the need for dual GPS installation and has the highest degree of accuracy in motion measurement for marine applications.

Specifications

POS MV 320

POS MV WaveMaster

POS MV Elite

¹ One Sigma, depending on quality of differential corrections
² Whichever is greater, for periods of 20 seconds or less

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

RRS James Cook cruise JC187 navigation data processing procedures

Originator's Data Processing

The data were logged by the TECHSAS (TECHnical and Scientific sensors Acquisition System) version 5.11 data logging system which is the main data logging system on NMF-SS operated research vessels. Data were processed using the National Oceanography Centre data processing routines into daily NetCDF files, and these TECHSAS (NetCDF) navigation and bathymetry files provided to BODC were used for BODC processing. Please refer to the cruise report for more information.

Bathymetry

The EA640 was used with a constant sound velocity of 1500 ms^-1 throughout the water column to allow it to be corrected for sound velocity in post processing.

The EM122 was fed attitude and position data from the Seapath 330+ system due to its superior real time heave.

Files delivered to BODC

BODC Data Processing

The data were reformatted to the BODC internal format using standard banking procedures, and averaged at 60 second intervals. The following table shows how variables within the files were mapped to appropriate BODC parameter codes:

*-*-position-POSMV_GPS.gps

*-*-gyro-POSMV_GYRO.gyr

*-*-sb_depth-EM122_DEPTH.depth

*-*-EA600-EA640_DEPTH.EA600

Position

A check was run on positional data to identify gaps and improbable values (through the calculation of speed). No gaps in the positional data were identified.

Ship Velocities

Ship velocities were calculated from the main latitude and longitude channels using standard BODC procedures.

Distance Run

Distance run was calculated from the latitude and longitude channels, starting from the beginning of the file, using BODC standard procedures.

Bathymetry

Bathymetry data from the EM 122 multibeam echo sounder were deemed to be the best quality, and were screened independently. The EM 122 multi-beam was run with a local sound velocity correction. The EA 640 single-beam appeared more noisy.

GEBCO

GEBCO bathymetry was added to the file using the main latitude and longitude channels. Multi-beam bathymetry data were compared to the GEBCO channel for agreement.

Calibrations

Field Calibrations

No field calibrations were applied to the data at BODC.

Screening

All reformatted data were visualised using the in-house EDSERPLO software. Where calibrations had been applied, only the calibrated versions of those parameters were screened. Suspect data were marked by adding an appropriate quality control flag.

Project Information

How do deep-ocean turbidity currents behave that form the largest sediment accumulations on Earth?

Background

Seafloor flows called turbidity currents form the largest sediment accumulations on Earth (submarine fans). They flush globally significant amounts of sediment, organic carbon, nutrients and fresher-water into the deep ocean, and affect its oxygen levels. Only rivers transport comparable volumes of sediment across such large expanses of our planet, although a single turbidity current can transport more sediment than the combined annual flux from all of the World's rivers combined. This project aimed to improve understanding of turbidity currents, and their wider impacts, by making the first detailed measurements of turbidity currents that runout into the deep (2-5 km) ocean. This project followed recent successful tests of new methods and technology for measuring turbidity currents in shallower (less than 2 km) water, which can now be applied to deep-water, large-scale submarine fan settings. Such measurements at 2 km water depth are the deepest yet for turbidity currents. Surprisingly, they showed that individual turbidity currents lasted for almost a week, and occupied 20% of the time. This was surprising because all previously measured oceanic turbidity currents lasted for just a few hours or minutes, and occurred for <0.1% of the total time. It suggests that turbidity currents that runout into the deep ocean to form major submarine fans may differ from their shallow water cousins in key regards. Preliminary measurements from 2010 and 2013 showed how monitoring is feasible for the study area here, the Congo Canyon off West Africa. The overall aim was to show how deep-sea turbidity current behave using the first direct measurements, and understand causes and wider implications of this behaviour.

This project set out to answer the following key questions about flow behaviour:

1. What controls flow duration, and does flow stretching cause near-continuous canyon flushing? We will test a new hypothesis that predicts flows will stretch dramatically as a 'hot spot' of faster moving fluid runs away from the rest of the event, thereby producing near-continuous flushing of submarine canyons.
2. What controls runout and whether flows become more powerful? We will test whether turbidity currents tend towards one of two distinct modes of behaviour, in which they erode and accelerate (a process termed ignition), or deposit sediment and dissipate.
3. How is flow behaviour and character recorded by deposits? This is important because deposits are the only record of most turbidity currents.
4. How does flow behaviour affect the transfer and burial of terrestrial organic carbon in the deep-sea? It was proposed recently that burial of terrestrial organic carbon in the deep sea is very efficient, and an important control on long-term atmospheric CO2 levels. This hypothesis implies little fractionation of terrestrial organic carbon occurs during submarine transport. Composition of organic carbon buried by the offshore flows is similar to that supplied by the river. We will test this hypothesis by analysing amounts and types of organic carbon along the offshore pathway in both flows and deposits.

Fieldwork

Data were collected on James Cook cruise JC187 between August and October 2019. Eight moorings were deployed along the Congo Canyon at warer depths of 2 to 5 km to measure frequency, duration, and run-out distance of multiple flows; together with their velocity, turbulence and sediment concentration structures; as well as changes in water, sediment and organic carbon discharge.

Participants

• Professor Peter Talling (Principal Investigator - Parent Grant) Durham University
• Dr Mattieu Cartigny (Co-Investigator) Durham University
• Professor Robert Hilton (Co-Investigator) Durham University
• Professor Jim McElwaine (Co-Investigator) Durham University
• Professor Daniel Parsons (Principal Investigator - Child Grant) University of Hull

Funding

This project was funded by Natural Environment Research Council parent and child grants NE/R001952/1 and NE/R001960/1, entitled 'How do deep-ocean turbidity currents behave that form the largest sediment accumulations on Earth?', with the former, parent grant led by Professor Peter Talling, Durham University, and the latter child grant led by Professor Daniel Parsons, University of Hull.

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: