Metadata Report for BODC Series Reference Number 1719029

• 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

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

Lockheed Martin Sippican T-5 XBT Probe

The Expendable Bathythermograph system uses a sea water ground. As soon as an electrode within the nose of the expendable probe makes contact with the water, the circuit is complete and temperature or sound velocity data can be telemetered to the ship-board data processing equipment. The T-5 XBT Probe can be used within a maximum depth of 1830 m, with a rated ship speed of 6 knots and has a vertical resolution of 65 cm.

Manufacturer specifications can be found here

Expendable bathymetric thermograph (XBT): Originator's processing

Sampling Strategy

FS Sonne cruise SO215 was funded by the NERC project 'The Louisville Ridge-Tonga Trench collision: Implications for subduction zone dynamics'. The cruise set sail on 25 April 2011 from Auckland, New Zealand to the Louisville Ridge before returning to Townsville, Australia on 11 June 2011.

Sample Collection

A series of T5 expendable bathymetric thermographs were deployed throughout the cruise to map the temperature and velocity (once ground-truthed to the sound velocity profile) of the water column in a rapid and more versatile manner than is possible using a sound velocity probe alone.

Several probes were deployed along each profile. Once cross calibrated against the sound velocity profile these could provide water column velocity throughout the study area and for every seismic profile.

Data processing

Depth is measured as a proxy of elapsed descent time through the water column.

Sound velocity is derived from the measured temperature data with an assumed constant salinity of 35 PSU (once ground-truthed to the sound velocity profile).

Calibrations

The .EDF files (calculated sound velocity profiles) generated by the XBT system software were transferred to the multibeam swath bathymetry data processing to provide water column velocity for every seismic profile.

The cruise report and data files have been examined and BODC is not aware that any further corrections were applied to the data.

Expendable bathymetric thermograph (XBT): Processing by BODC

The XBT data were supplied to BODC in ASCII files with two files for each probe deployed (raw .RDF and processed .EDF). BODC have processed the .EDF files. The following table shows how the variables within the files were mapped to appropriate BODC parameter codes:

The reformatted data were visualised using the in-house visualisation software. Suspect data were marked by adding an appropriate quality control flag. Missing data are set to an appropriate value and the corresponding flag added.

Project Information

The Louisville Ridge-Tonga Trench collision: Implications for subduction zone dynamics

Background

The plate tectonics paradigm provides the fundamental model for the destruction of oceanic lithosphere at subduction zones. But the dynamics of subduction zones are also responsible for the construction of arc lithosphere whose features include some of the largest and most active volcanoes on Earth and the majority of large earthquakes.

The Tonga-Kermadec island arc-deep-sea trench system is an ideal study site as it is the most linear, fastest converging and most seismically active of any of the world's subduction zones, and the system has evolved over a long period of geological time (>50 Myr).

This NERC funded project NE/F004273/1 will provide unique models of crustal structure throughout the collision zone and obtain the necessary direct observations to parameterise and constrain numerical modelling of the thermo-mechanically coupled visco-plastic-elastic response of the lithosphere and the distribution of deformation within the subducting and overriding plates. The observations and measurements on which this study is based will be made during an expedition to the collision zone by a research ship.

Scientific Objectives

The key scientific objectives for the cruise were as follows:

• Determine the 'background' crustal and uppermost mantle structure of the subducting plate.
• Determine the crustal and uppermost mantle structure across and along the Louisville Ridge.
• Determine the physical properties of the leading edges of the subducting and over-riding plates.
• Determine the state of isostasy, ridge-related flexure and moat characteristics at the Louisville Ridge, and the mechanical properties of the subducting and over-riding plates.
• Determine the seafloor morphology and collision-related deformation in the Tonga forearc.

The scientific objectives were addressed by an integrated marine geophysical experiment that comprises simultaneous seismic reflection (MCS) and wide-angle (WA) refraction, gravity, magnetic, bathymetry and sub-seabed high-resolution imaging of the Louisville Ridge-Tonga-Kermadec Trench collision system.

Fieldwork

Instrumentation

Types of instrumentation and measurements associated with this project:

• Ocean-Bottom Seismographs (OBSs)
• Magnetics measurements- SeaSpy
• Gravity - LaCoste-Romberg - Air-Sea meter
• Multichannel reflection seismic data - Sercel SEAL
• Wide-angle refraction seismic data - 4 component OBS
• Swath bathymetry - Simrad EM120
• Atlas Parasound PS 70
• Expendible bathymetric thermograph

Contacts

For further information on the project contact:

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: