A Mooring Under Ice

Changes in the fresh water flowing from the Arctic region, through Hudson Strait, and into the North Atlantic can affect ocean circulation and climate. Fresh water (blue) is less dense and flows above saltier (red) water. Anchored to the seafloor 180 meters (590 feet) deep, a mooring held a variety of instruments: An experimental device called the Arctic Winch (atop the red flotation sphere) periodically rises toward the surface to obtain critical measurements in the top 50 meters, where fresh water flows just beneath the ice. The winch comes back down immediately if it hits ice or the surface, so that ice or icebergs don’t sweep it away. An upward-looking sonar measures ice thickness. A moored profiler (yellow) moves up and down the line every two hours, measuring water temperature and salinity. An acoustic Doppler profiler measures current speeds and directions. (Animation by Jack Cook, Woods Hole Oceanographic Institution)