Equipment

We will use two main types of equipment: a deep-towed geophysical instrument called TOBI (Towed Ocean Bottom Instrument) for mapping the different types of rocks and seafloor structures, and a specialist Rock Drill which is lowered on a wire to the seabed and can take oriented samples.

TOBI

TOBI is towed about 300 m above the seafloor, so is much closer to the bottom than the towing ship, since the sea where we work is usually several kilometres deep. It is about 3 m long, weighs 1 ton in air, but is neutrally buoyant in water. It carries two sensors that are particularly important for our work: A sidescan sonar that emits sound in a broad fan to image the texture of the seafloor, and a magnetometer for measuring tiny variations in the Earth’s magnetic field.

We will combine the sidescan with existing topographic data to produce a 3-D model of seafloor texture, and interpret that to produce a high-resolution geological map showing the occurrence of different rock types (specifically mantle peridotites and crustal basalts) and of tectonic faults. The magnetic data can be used both to produce very high resolution histories of the precise separation rates of the tectonic plates, and to help identify different rock types on the seafloor.

Rock Drill

The BRIDGE Rock Drill was developed by British mid-ocean ridge scientists in collaboration with the British Geological Survey to obtain short, oriented cores of hard-rock material from the seafloor. It allows us to take core up to a few metres long but, unlike other seafloor coring devices, it marks the north direction on the sample.

Subsequent analyses can then determine, for example, the direction in which minerals are aligned (showing how the rock flowed during its emplacement) or, by measuring the direction of the rock’s magnetisation, any rotations it has undergone.