With only one-quarter of the sea floor mapped with sonar, it is impossible to know how many seamounts there are. However, radar satellites that measure ocean height can also find them, by looking for subtle signs of seawater mounding above a hidden seamount, tugged by its gravity. A 2011 study using the method found more than 24,000. High-resolution radar data has now added more than 19,000 new ones.
Seamounts often occur in chains formed as tectonic plates shift over stationary plumes of hot rock rising from the mantle. This catalog will pay immediate dividends for studies of the Earth’s interior. It has identified new seamounts in the northeast Atlantic Ocean that could help track the evolution of the mantle plume that feeds Iceland’s volcanoes. The study also spotted seamounts near a ridge in the Indian Ocean where fresh crust is made as tectonic plates spread apart. This shows a surprising amount of volcanism in a region once thought to me magma starved.
The maps will be most important in understanding the ocean’s global conveyor belt of currents. The currents transfer heat from the equator to the poles, where the water cools and gains density until it plunges downward, carrying heat and carbon dioxide into the abyss.
When ocean currents swirl around seamounts, they create turbulent “wake vortices” that can provide the energy to push cold water up, says oceanographer Jonathan Gula. He found that these wake vortices make seamounts the leading contributor to upward ocean mixing and a key player in climate.