Advancing seafloor sampling using submersibles and remotely operated vehicles: The cross-line laser orientation method

Paleomagnetism has played a crucial role in unraveling processes such as plate motion and the emplacement of volcanic products. Despite its significance, a full range of such studies have not been possible for samples from the oceans, primarily due to the technical obstacles associated with obtaining oriented samples from the seafloor. Here we devised a rapid and uncomplicated technique for collecting oriented samples from the seafloor utilizing a cross-line laser system installed on the biaxial pan-tilt unit of the human occupied vehicle (HOV) SHINKAI 6500. This system comprises one laser capable of projecting a vertical line with horizontal mobility, together with a second laser positioned perpendicular to the vertically oriented beam, allowing flexibility to adjust its projection both upward and downward. The center of the cross-line laser is focused on a target rock or sediment corer. Orientation of the cross-line laser is calculated from the positions of SHINKAI 6500 and the pan-tilt unit, which are recorded every second. An accurate restoration of the collected sample to its original orientation can be achieved based on the laser path marked on the rock surface and the laser orientation data. We collected rocks and sediments from the seafloor of the Okinawa Trough in order to test our new orientation method and conducted paleomagnetic measurements on them. Paleomagnetic directions of the rocks are roughly consistent with the Earth's current magnetic field direction, proving validity of the method. This innovative method has the potential to become widely adopted for collecting oriented samples from seafloor using a HOV and remotely operated vehicle (ROV).