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Moorings & Buoys

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The Ocean Observatories Initiative (OOI) program successfully deployed moorings off the New England Coast, marking the first comprehensive test of an OOI system on the East Coast. (Photo by John Lund, Woods Hole Oceanographic Institution)

Many ocean processes that scientists want to study are either invisible from the surface or they play out over long periods of time and wide geographic expanses. Measurements from a ship only provide a brief snapshot or a short glimpse of conditions. As a result, oceanographers find they often need to send instruments deep beneath the surface for long periods of time to measure water properties and record data to quantify changing conditions in the ocean.

To obtain this longer view, ocean scientists and engineers often deploy moored instruments or buoys. An oceanographic mooring consists of a long line or cable with an anchor at one end, a float at the other, and instruments attached to the line in between or to a float at the surface. These allow researchers to measure such properties as water velocity, salinity, and temperature in several places and for long periods of time. They also allow scientists to explore the complex interactions between the ocean and atmosphere that are difficult to monitor from satellites.
The anchor keeps the mooring in one place, and the float keeps the line vertical in the water column. The float may bob on the surface, in which case it is a buoy, or, below the surface to keep the line stationary and out of the way of ships. Surface buoys can hold meteorological instruments such as rain, sun, and wind gauges. They can also hold communications equipment that permits scientists to monitor information from instruments far from land in real-time.

Surface buoys, moored systems, and the instruments they carry are very challenging to design and deploy. The cables can be more than three miles long, and the instruments and floats have to withstand corrosion, freezing cold, pressure up to 10,000 pounds per square inch, powerful currents, surging waves, and even fish that mistake them for food.

Buoys and moorings have been deployed singly or in lines across key areas such as the Gulf Stream. They have also been placed in vast arrays to blanket a large area of the ocean with instruments. In the 1970s and 1980s, several large ocean science projects used moored instruments to reveal major current systems such as the ocean conveyor in the North Atlantic that play a critical role in Earth’s climate system. Buoys and moorings also provide continuous data from hard-to-reach places about critical processes such as the movement of tsunamis across ocean basins or the air-sea interactions in the central Pacific that produce El Niño and La Niña events.

Ocean scientists and engineers are currently developing even more sophisticated mooring arrays as part of the Ocean Observatories Initiative. Some will serve as “home base” for autonomous underwater vehicles; others will act as automated chemistry and biology laboratories in the sea.