The Geophysics Team

The geophysics team processes and interprets the magnetic data collected by magnetometers and the data acquired with the ship's two gravimeters.

 

Marine magnetic recordings have produced evidence of the polarity inversions of the Earth’s magnetic field recorded by the ocean crust during its formation on the dorsal axis. The symmetrical sequences of magnetic anomalies on each side of the ridge allow to date the ocean floor and reconstruct its evolution by repositioning the tectonic plates in their previous positions using these markers.

In addition to this now classic aspect of marine magnetics, magnetometers installed on the submersible vehicles of the French Oceanographic Fleet provide high-resolution data that highlight smaller objects, inaccessible through surface data.

Of these objects, hydrothermal sites are a prime target and are at the heart of the HERMINE2 expedition. Previous work has shown that sites with basaltic substrate are characterized by a strong decrease in magnetization of the basalt and therefore a negative magnetic anomaly, whereas sites with mantellic substrate have strong magnetization and a positive anomaly. Magnetism makes it possible to detect and characterize these sites.

Gravimetry is the measurement and study of gravity on the Earth’s surface, and it has provided a better understanding of the structure of the ocean crust. The Bouguer anomaly has shown that the construction processes of the crust at the slow-spreading ridge axis, such as the North Atlantic Ridge, are variable in time and space, with places where the crust is thin alternating with those where the crust is thicker. The data acquired with the vessel’s instruments during this expedition complement existing data and will be used to better understand the structure of the ocean crust in our study area. A gravimeter for submersible vehicles is in development and has not yet been adapted for the AUV.

  • Jérôme Dyment, research specialist in marine magnetic data analysis, IPGP/CNRS
  • Florent Szitkar, research specialist in marine magnetic data analysis, Geological Survey of Norway (NGU)
  • Marcia Maia, geophysicist, specialist in gravimetry and mid-ocean ridges, Geo-Ocean/CNRS