Metadata Report for BODC Series Reference Number 1964860

• 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 JC156 Navigation Quality Control Report

Bathymetry

The EM122 multi-beam echosounder contains noise and drop outs. The EM122 multi-beam recordings follow the baseline bathymetry data provided by GEBCO when drop outs and noise are not present.

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

RRS James Cook cruise JC156 Underway Document

Cruise Details

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 JC156 Navigation Instrumentation

Instrumentation

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 JC156 Navigation Data Processing Procedures

Originator's Data Processing

The data were logged by the TECHSAS (TECHnical and Scientific sensors Acquisition System) system into daily NetCDF files. The TECHSAS system is used as the main data logging system on NMF-SS operated reserach vessels. The daily TECHSAS NetCDF navigation and bathymetry files provided to BODC were used for BODC processing. Data were additionally logged into the RVS Level-C format files which have been archived at BODC.

Files delivered to BODC

BODC Data Processing

Data were banked at BODC following standard banking procedures. Data were averaged to 60 second intervals.

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

yyyymmdd-000000-position-POSMV_GPS.gps

yyyymmdd-000000-gyro-POSMV_GYRO.gyr

yyyymmdd-000000-sb_depth-EM122_DEPTH.depth

yyyymmdd-000000-EA600-EA640_DEPTH.EA600

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). There was one gap in the positional data at the start and end of the file, produced during loading to the BODC system. These gaps were trimmed after processing was complete.

Ship Velocities

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

GEBCO

GEBCO bathymetry was added to the file using the main latitude and longitude channels.

Distance Run

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

Bathymetry

Bathymetry data were screened independently as well as against GEBCO bathymetry measurements. Both the EM122 multi-beam echosounder and the EA600 single beam echosounder contain a significant amount of noise. The EA600 single beams data is particularly unreliable as it regularly provides readings that are unrealistic and inconsistent with the EM122 multi-beam recordings. In addition, the EA600 single beam does not follow the baseline bathymetry data provided by GEBCO.

Calibration

No field calibrations have been applied.

Project Information

FRidge: The impact of Mid-Ocean Ridges on the Ocean's Iron cycle

FRidge is a research project funded by the UK Natural Environment Research Council (NERC). It aims to explore hypotheses regarding the mechanisms that shape ocean iron distribution and in particular, the role of hydrothermal inputs from distinct vent sites along the Mid-Atlantic Ridge.

The project is part of the UK contribution to the international GEOTRACES programme. Research will take place along the GEOTRACES International Section GA13.

Introduction

Photosynthesis by marine phytoplankton contributes to the partitioning of carbon dioxide between the atmosphere and the ocean. Iron is essential for phytoplankton growth as it is required for a number of important enzymes that participate in both photosynthesis and respiration. Mid-ocean ridges are significant sources of iron to the ocean due to hydrothermal activity, with dramatic iron plumes that persist for thousands of kilometres away from the ridge.

The impact of hydrothermal iron on the ocean carbon cycle depends both on the longevity of the iron plumes and the mixing of iron into surface waters, with both aspects poorly constrained. Thus our understanding of how the ocean iron cycle functions is incomplete. This is important as the influence of ocean biology on ocean-atmosphere carbon dioxide exchanges via the biological pump is controlled by iron availability over large parts of the ocean.

Scientific Objectives

The main objectives of the project are to:

1. Document the changes in iron supply, cycling and speciation along the diverse hydrothermal systems of the northern Mid-Atlantic Ridge.

2. Link observational science with state of the art ocean modelling to assess the global influence of mid-ocean ridges on the ocean iron cycle and the sustenance of surface productivity.

To deliver on these objectives, a research expedition to the Atlantic Ocean was carried out to measure trace metals, nutrients and ocean physics over and around the Mid-Atlantic Ridge. Ultimately this will be able to address the broader question of how the amount of iron from mid-ocean ridges can influence phytoplankton growth in the open ocean.

Fieldwork

The FRidge cruise was completed aboard RRS James Cook cruise JC156, which ran between Southampton and Guadeloupe from the 20th of December 2017 to the 1st of February 2018. See the table below for details on what was sampled:

The above images show the locations of known hydrothermal vent systems and the dots represent locations where sampling took place.

Project Collaborators

The science delivered as part of this GEOTRACES section is greatly enhanced by the collaboration with a number of scientists from the following institutions:

- University of Southampton

- University of Liverpool

- Plymouth Marine Laboratory

- Oxford University

- University of South Florida

- University of Washington

- University of California Santa Barbara

- Woods Hole Oceanographic Institute

Scientific Personnel

- Alessandro Tagliabue (Cruise Chief Scientist, University of Liverpool, UK)

- Maeve Lohan (University of Southampton, UK)

- Andy Heath (University of Liverpool, UK)

- Alastair Lough (University of Southampton, UK)

- Shaun Rigby (University of Liverpool, UK)

Project Partners

- Alex Baker (University of East Anglia)

- William Jenkins (Woods Hole Oceanographic Institute)

- Brandy Toner (University of Minnesota)

Funding

This is a NERC funded research project. Funding was provided in the form of two fellowship and training grants.Total value of £527,588. The lead/parent grant reference number is NE/N010396/1 led by Maeve Lohan and the child grant NE/N009525/1 is led by Alessandro Tagliabue.

Period of Award: 4 Sep 2017 - 3 Mar 2020

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: