NASA’s Oceans Melting Greenland (OMG) is a five-year campaign to study the glaciers and ocean along Greenland’s 43,000-kilometre coastline. Its goal is to find out where and how fast seawater is melting the glacial ice. Most of the coastline and seafloor around the ice sheet had never been surveyed, so the 2016 flights expanded scientists’ knowledge of Greenland significantly.
The water circulating close around the Greenland ice sheet is like a cold river floating atop a warm, salty ocean. The top 200 metres of colder water is relatively fresh and comes from the Arctic. Below that is saltwater that comes from the south, 3 to 4 ºC warmer than the fresher water above. The layers don’t mix much because freshwater weighs less than saltwater, so it stays afloat.
If a glacier reaches the ocean where the seafloor is shallow, the ice interacts with frigid freshwater and melts slowly. Conversely, if the seafloor in front of a glacier is deep, the ice spills into the warm subsurface layer of saltwater and may melt relatively rapidly. Satellite remote sensing can’t see below the surface to discern the depth of the seafloor or study the layers of water. OMG makes these measurements with shipboard and airborne instruments.