The TOSCA geological and biological research survey took place over May - June 2018 on board the RV Celtic Explorer with the mission of studying the Mid-Atlantic Ridge, a complex area located 1,600km west of Ireland deep in the Atlantic Ocean. Led by University College Dublin (UCD) with Geological Survey Ireland (GSI) and the UK's National Oceanography Centre (NOC), marine surveying equipment including Ireland’s marine robot, the Holland 1, was used to characterise an important part the ocean, called the Charlie-Gibbs fracture zone. The Charlie-Gibbs fracture zone consists of two large scale cracks called fracture zones, visible on the seabed, that cross the Atlantic from Ireland to Newfoundland. These parallel cracks are 40 km apart on both the American and European tectonic plates and they continue to separate at about the rate your fingernails grow, from the centre of the Atlantic at the Mid-Atlantic Ridge. The cracks, or fracture zones, offset the Mid-Atlantic Ridge by 370km, and characterise a unique style of spreading between them that result in Alpine scale mountains, 4km high. During the cruise, seismic reflection geophysics surveys and acquired sub-bottom acoustic profiles weer carried out. Multiple ROV dives were completed where video data of the seafloor geology and biology was acquired along with sample collection. The multibeam echosounder mounted on the ROV also allowed for mapping of the seafloor at a much higher resolution (5m) compared to using a similar multibeam mounted to the ship’s hull. Over the course of the TOSCA project, the ROV collected approximately 4,600 images, 67 hours of HD video and a total of 3.3Tb of data. The purpose of TOSCA (Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone) expedition’s mission was to study a complex part of the Atlantic, 1600km west of Ireland by mapping the seabed in high-resolution, as well as using seismic equipment and gravity corers to investigate below the seabed.