Subduction studies in the North East Atlantic
Yves Desaubies
IFREMER
A major field experiment, dubbed POMME, is planned for the year 2000 - 2001 in the North East Atlantic, to study the process of subduction in the intergyre region (between the subpolar and subtropical gyres). Several French laboratories will take part in this experiment, which will include physical and biogeochemical oceanography, as well as meteorological, observations. The main emphasis is on the role of mesoscale processes in the formation and subduction of mode water, and the impact on biogeochemical processes. Several cruisees are planned. Five moorings will be set, with current meters, T end C sensors, ADCPs, and acoustic tomography. Several floats (acoustically tracked, and profiling) will be deployed. The analysis will be based on a Kalman filter assimilation, including all the relevant observations, to reconstruct the time evolving mesoscale structure of the circulation and heat fluxes.
Global Ocean Acoustic Monitoring and the CTBT
Martin Lawrence
CTBTO, Vienna International Centre
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) to ban all nuclear explosion tests was opened for signature in 1996. Verification of compliance with the CTBT requires establishment of a global network of sensors to detect, locate and identify the signal generated by a nuclear explosion in any environment. Monitoring of the world's oceans is primarily provided by a hydroacoustic network to be established for this purpose.
Implementation of the monitoring networks began with establishment of the CTBTO Provisional Technical Secretariat (PTS) in Vienna in March 1997, although a critical mass of staff were not in place until late 1997. This presentation will describe the status of the stations of the hydroacoustic network that are identified in the Treaty.
The hydroacoustic network is based upon 11 stations that will provide hydroacoustic monitoring of the world's oceans for 24 hours a day, every day of the year, into the indefinite future. This unique resource will utilise two types of hydroacoustic station: hydrophone and T-phase.
A hydrophone station is based on an ocean-deployed hydrophone sensor working at the frequency range from 1 Hz to 100 Hz. The hydrophone sensor elements are at a fixed depth near the axis of the SOFAR channel, floated from an ocean-bottom anchor and cabled back to shore.
A T-phase station is based on an island-deployed seismometer sensor. Each T-phase station is sited near the shore of a small island with steep bathymetry. It relies on the detection of a signal that has propagated predominantly through the ocean, but has been converted to seismic energy at the margin of the island.
Most hydroacoustic stations identified in the Treaty require a new station to be built. However, some stations existed prior to the Treaty, but need upgrading. Work has began on site surveys and installations at some stations. Progress and plans will be discussed.
