TOSCA travels to the Mid-Atlantic ridge and discovers an other-worldly landscape

The UCD-led TOSCA expedition returns to Galway on World Ocean day, having spent 3.5 weeks at the Charlie-Gibbs Fracture Zone of the Mid-Atlantic Ridge.

The Charlie-Gibbs Fracture Zone consists of two huge parallel cracks in the crust of the Atlantic Ocean running between Ireland and Newfoundland. The faults are named after the US Coast Guard weather Station Charlie and the USNS Josiah Willard Gibbs oceanographic research vessel. It’s the longest-lived fracture zone in the Atlantic, and the most prominent feature interrupting and offsetting the Mid-Atlantic Ridge; it took 90 million years to attain its current length. These fracture zones are similar to the San Andreas fault in the western US and the North Anatolian fault in Turkey and Greece with large earthquakes taking place here regularly. Yet, until TOSCA, there have been no geological studies in the area and hardly anything is known about this feature.

Atlantic Ocean Research Alliance data guided the TOSCA team to plan a month-long survey at the spreading centre of the CGFZ. The team discovered that between the fractures the seafloor is being stretched by multiple faults causing the Atlantic to continuously grow in this location. Against the standard model for stretching that tends to break and flatten material, the seafloor here rises in a never before known mountain range, with peaks as high as 4000 m, but never breaking the sea surface. These mountains are known as oceanic core complexes and have been found elsewhere along the Mid-Atlantic Ridge and the Indian Ocean, but those do not exhibit the dramatic morphologies encountered at CGFZ. Three of the mountains were visited by the TOSCA marine expedition with the RV Celtic Explorer. 500-1000m high scarps were discovered that have been produced by catastrophic rock avalanches, with giant boulder fields spilling into the fractures.

150 rock samples amounting to roughly 200kg were collected with the Holland I remotely operated vehicle, along with 86 hrs of video footage. Over 10,000km² were mapped, which is almost the size of Co Galway and Co Mayo together. This dataset will be made available to the open source Atlantic Ocean Research Alliance.

The mountains are hosts to abundant sea life, fish, corals, sponges. This pristine environment, being so far from any coast has not suffered too much from human impact, although some glass bottles and fishing nets were found. Spectacular sponge gardens and even a skate “nursery” with more than 70 skate eggs were found which is a first for the deep sea.

The team of scientists that make up TOSCA come from five different countries (Ireland, UK, Germany, Canada and Greece), each with different scientific expertise. They will now travel back to their respective institutes to analyse all the data and work out how the mountains were formed, when and how the rock avalanches take place and how the geology affects the local fauna.

Quote from Chief Scientist Dr Aggie Georgiopoulou: We are always amazed by the discoveries we make on our oceanographic expeditions, but what we have found at the Charlie-Gibbs Fracture Zone surpassed all of our expectations! It is overwhelming to realise how many things we still don’t know about how our planet works. Our expedition and the data we collected show that there are so many discoveries awaiting to be made in the depths of our oceans.

Acknowledgments for funding, data and support: AORA, Marine Institute, DFG (German Science Foundation)

Affiliations: University College Dublin, Geological Survey Ireland, National Oceanography Centre, University of Southampton, Christian-Albrechts University of Kiel, Memorial University Newfoundland, University of Athens, NUI Galway, Queen’s University Belfast, Irish Marine Institute