4/7/2023 0 Comments Iceberg alley![]() ![]() ![]() Helheim Glacier and many others around Greenland are slow-moving rivers of ice that drain the Greenland Ice Sheet into fjords. On a mobile device? Illustrations by Jack Cook, Woods Hole Oceanographic Institution Ice sheets and sea level rise The mooring was specially designed to stop short of the surface to lessen the chances of iceberg collisions, though obviously it could not avoid them all. The mooring ended 1,000 feet below the surface with a buoyant float-an orange, metal sphere that holds the whole apparatus upright. The lower half of SF1 looked like a standard oceanographic mooring, but unlike many moorings, it had no buoy at the ocean surface. We also deployed several other moorings elsewhere in the fjord, in safer locations much farther from the glacier. At the top, a buoyant top float would stretch a vertical but flexible, ¼-mile-long cable strung with instruments measuring water temperature, salinity, pressure, and velocity. If all went well (though there is no way to tell at deployment), the anchor would end up at the bottom. Last, we attached the anchor and released the whole contraption.Īs it fell to the seafloor, the anchor pulled the string of instruments, wires, and floats into the fjord’s abyss. Then, piece by piece, we connected and snaked out SF1’s various components along the water’s surface, starting from the top: floats, wire, instrument, wire, another instrument, wire, instrument, and so on. First, we surveyed the area for a promising location, using an echo sounder that bounces sound waves off the seafloor. Setting up a tower of underwater instruments is no small feat. In this deep water near Helheim Glacier, our team, led by scientists Fiamma Straneo of Woods Hole Oceanographic Institution (WHOI) and David Sutherland of the University of Oregon, assembled Sermilik Fjord Mooring No. But in Greenland, the cliffs that line the fjords extend far beneath the ocean surface, forming underwater canyons that connect the open ocean to glaciers. You would need go hundreds of miles offshore of New England to reach water this deep. Sermilik, one of the many fjords on the east coast of Greenland, is long (60 miles), narrow (4 miles wide) and deep (½ mile). This narrow coastal inlet, abutted by steep cliffs, connects at one end to the open ocean at the other end, the vertical ice face of the glacier forms a back wall nearly 2,000 feet tall. This may not seem like a safe location for scientific equipment, but our research group deliberately placed SF1 in the line of iceberg fire in Sermilik Fjord, 20 miles from the terminus of Helheim Glacier. Usually, these chunks of ice-sometimes as tall as a skyscraper and as wide as seven city blocks-would hold down SF1 for several hours and then move along, allowing SF1 to resiliently float back up. They pushed down underwater scientific instruments on the long mooring line toward the seafloor in a Greenland fjord. For 13 months, icebergs had plowed over Mooring SF1, again and again. The fatal blow was definitely not the first hit. ![]()
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