OHA-SIS-BIO - OBSERVATOIRE HYDROACOUSTIQUE
|Type||Set of cruises|
|Chief scientist(s)||ROYER Jean-Yves|
|Project manager||ROYER Jean-Yves|
OHA-SIS-BIO - Observatory of HydroAcousticity from SISmicity and Biodiversity in the Indian Ocean - is a long-term hydroacoustic program for monitoring the seismic activity and the vocal activity of large marine mammals in the southern Indian Ocean. A network of autonomous hydrophones (9 moorings, 10 hydrophones) has been deployed and yearly maintained since 2010 between La Réunion, Crozet, Kerguelen and Amsterdam islands, taking advantage of the yearly journey of R/V Marion Dufresne to these southern islands.
The hydrophone array is designed to continuously monitor the earthquake activity associated with 3 contrasted spreading ridges (16 to 70 mm/yr) and with the intraplate deformation in the southern Central Indian Basin. This approach is very effective for detecting and locating low magnitude (>2.5) earthquakes, which are not recorded by the land-based seismological networks, and for deciphering magmatic from tectonic events. The objectives are to characterize the seismic climate of mid-oceanic ridges with ultra-slow, slow and intermediate spreading rates, and the temporal and spatial distribution of the intraplate deformation.
This observatory is also designed to monitor the vocal activity of large baleen whales. Passive acoustics is a very effective tool for monitoring the presence of these acoustically very active marine mammals. At least 5 populations of blue whales are detected by our network. The objective is to improve knowledge of the presence, abundance and seasonal migrations of these large marine mammals, classified as endangered, over several annual cycles in the Southern Indian Ocean.
Our data also display unexpected information on the sea-state and icebergs (calving, collision, dislocation). These two applications also require long time-series to validate sea-state prediction models or to monitor the evolution of the oceanic ambient noise (natural or man-made).
All these objectives have in common that they require low-frequency hydroacoustic recordings (< 120 Hz) and continuous time series as long as possible to be representative of the seismic regime of spreading ridges, the whale activity or changes in ambient noise, in these remote and inaccessible parts of the world ocean.
This program is supported by the French Research Fleet, the CNRS (INSU), the University of Brest, and the Regional Council of Brittany.
Fin whale and tabular iceberg off the southern Kerguelen Plateau (taken in January 2010 by 58°S from R/V Marion Dufresne).
North : 25.0
South : -50.0
West : 50.0
East : 120.0