LAUSR

The Earth’s oceans form a continuous body of saltwater covering more than two thirds of the planet and storing 97% of its water. With an average depth of about 3,700 m (Charette and Smith 2010), the oceans are widely considered to be Earth’s final frontier. They control global climate and weather and have provided humanity with many resources for millennia. Extending away from land, the oceans are divisible into three main regions: the continental shelf, where water depths are generally less than 200 m; the continental slope; and the flat or gently sloping abyssal plain, typically occurring at depths greater than 4,000 m (Fig. 1). Although a poorly defined term, the ‘deep’ ocean may be considered to be seafloor below 200 m where, with little penetration of sunlight, photosynthesis is not possible. The deep seafloor covers about 60% of the Earth’s surface and hosts a spectrum of geological settings, geomorphologic features and ecosystems. This diversity, and its long and dynamic history, results in the deep seafloor hosting mineral deposits that are both similar to those found on the continents as well as types unique to the oceans.