Ocean nerds love to say that we know more about the surface of the moon than we know about the depths of the ocean, but there's tons of places on Earth we know almost nothing about. In a discovery that really shows how little we know about the land under the world's great ice sheets, NASA says that their IceBridge scientific mission has discovered a nearly Grand Canyon-sized canyon, lurking all this time, under a mile of ice in Greenland.
Reporting their findings in Science, the scientists say the winding canyon is at least 460 miles long, actually a whole third longer than the Grand Canyon, and it goes as deep as 2,600 feet—only about half as deep. The canyon, which researchers surmise has been largely covered by ice for several million years, runs from nearly the center of Greenland out to its end in the Petermann Glacier fjord in northern Greenland. During the last interglacial period, 100,000 years ago, parts of the canyon would have been uncovered.
Prior to the formation of the Greenland Ice Sheet the scientists think it transported water from the interior of the island to the coast. Today, it's believed that the canyon helps transport meltwater underneath the glaciers from the interior to edge of the ice sheet as it meets the ocean.
The canyon was discovered by the IceBridge team, which used a radar depth sounder to practically "see" through the ice—the longer it took for the radar waves to bounce back from the bedrock under the ice, the deeper the canyon.
The Greenland Ice Sheet is the second-largest body of ice in the world, covering about 80 percent of the surface of Greenland. At its greatest depth it reaches 1.86 miles of ice, with much of it thicker than a mile and a quarter.
Part of the reason for the research that led to the discovery was to help shed more light on the possible contribution of the melting of the Greenland Ice Sheet to global sea level rise.
Should the entire ice sheet melt away it will lead to over 20 feet of sea level rise. How quickly that will happen is far less clear. Research from the Potsdam Institute for Climate Impact Research shows that if global average temperature rises past 2°C above pre-industrial levels, there's a greater than 50 percent chance that the ice sheet will melt completely. The time frame on this is still a little fuzzy; that could take place anywhere from 300 to 1,000 years from now. Other research from Potsdam, released earlier this summer, finds that under a 4°C temperature rise (something which looks increasingly certain) ice melt in Greenland will contribute 25 percent to global sea level rise—with melting ice in Antarctica contributing over half—but, again, this is something that could happen over the next several millennia.
The downsides to a thawed Greenland are clear—lost coastal cities, weather turning ever more unpredictable—but I guess we'd get to see what's been under all that ice for all this time. On the other hand, as these findings show, scientists can do that without flooding San Diego, so maybe we should go ahead and pass on that.