THE Mid-Oceanic Ridge, a broad fractured arch more than 40,000 miles long, is the largest tectonic feature on the surface of the Earth. Associated with the centre of the ridge over much of its length is an axial fracture or rift which is the locus of shallow earthquakes. An extension of this world encircling ridge into the Greenland Sea and Arctic Ocean was first hypothesized on the basis of a well defined pattern of earthquake epicentres and a few spot soundings1,2. The topographic form of the ridge was first revealed by precision depth records obtained during the pioneer polar crossings of the nuclear submarines Nautilus3 and Skate4. The Arctic Mid-Oceanic Ridge does not bisect the entire Arctic Basin but lies midway between the monolithic, aseismic Lomonosov Ridge and the Eurasian continental margin.