This exploration is the first of the 2013 field season for NOAA Ship Okeanos Explorer. The primary objective of this shakedown cruise is to operationally test the vessel, its systems, and all mission equipment. Another goal of this mission is to complete the comprehensive mapping of Northeast canyons and the adjacent continental shelf. The shelf break and slope off the northeastern U.S. support a diversity of habitats including more than 70 canyons ranging from depths of ~100 meters to ~3,500 meters. The canyons provide a refuge for a variety of fauna including species of deep water corals, fish and other animals. Gaseous cold-seeps have been found in some of these canyons.
These cold-seep communities may signal the presence of other unusual ecosystems, potentially important energy resources and areas that may be susceptible to submarine landslides that can trigger tsunamis.
Our first exploration targets during this cruise will be the deep water canyons that extend from Rhode Island north to Maine. Next we will move farther offshore to conduct mapping of several seamounts in the New England Seamount chain. Seamounts are important habitat for deep water corals and have significant impacts on deep ocean currents. Globally, there are over 100,000 unexplored seamounts. The data we collect will be the basis for further exploration.
The main technology that will be used for this exploration is multibeam sonar. Sonar systems are used to determine water depth, as well as to locate and identify underwater objects. In use, an acoustic signal or pulse of sound is transmitted into the water by a sort of underwater speaker known as a transducer. The transducer may be mounted on the hull of a ship, or may be towed in a container called a towfish.
If the seafloor or other object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer. The system measures the strength of the signal and the time elapsed between the emission of the sound pulse and the reception of the echo. This information is used to calculate the distance of the object, and an experienced operator can use the strength of the echo to make inferences about some of the object’s characteristics. Hard objects, for example, produce stronger echoes that softer objects. This is a general description of “active sonar”. “Passive sonar” systems do not transmit sound pulses. Instead, they “listen” to sounds emitted from marine animals, ships, and other sources.
