Ice moves. It flows in streams and channels. It creeps and compresses and deforms. We see it best perhaps in glaciers birthing icebergs, frozen rivers emptying into the ocean. Now, for the first time ever, we can see just how much ice moves across the entire Antarctic continent, and the view offers up a few big surprises. This new knowledge could help scientists understand how ice is changing now and how it will change as our climate continues to warm in the future. It will help scientists predict how much sea levels will rise as ice melts in coming decades.
This new view of Antarctica in motion comes from thousands of measurements taken by radar instruments on satellites from Canada, Japan, and the European Space Agency between 1996 and 2009. Eric Rignot of NASA’s Jet Propulsion Laboratory and the University of California Irvine led the team of scientists that pieced together the data to figure out how much each section of ice moves per year. An animation of the ice in motion is available from the NASA multimedia gallery.
The end result, shown here, reveals areas where ice moves as quickly as a few kilometers per year (shown in bright purple and red) and other areas where movement is confined to a few centimeters per year (shown in pink). The slowest moving ice is along the divides that separate glacier basins, which are outlined in black. These divides are generally over mountains that shape the flow of ice.
The fastest moving areas are glaciers and ice shelves along the edge of the ice, and of these, the Pine Island and Thwaites glaciers are moving most. The surprise, however, is that channels of fast-flowing ice extend far inland, broad tributaries feeding the glacial rivers.
The ice sheet around the tributaries moves slowly, compressed by its own weight and spreading like a mound of pancake batter. The wide tributaries, shown in blue are not quite as fast as an ice stream, but move faster than the ice sheet around them. This type of moderate-paced motion was a surprise to Rignot and his team.
“We are seeing amazing flows from the heart of the continent that had never been described before,” said Rignot in a NASA release. “This is like seeing a map of all the oceans’ currents for the first time. It’s a game changer for glaciology.”
The finding is a game changer because it adds another type of motion to the ice sheet. Previously, scientists have thought that ice sheets move largely because they are deforming under their own weight, pushing ice to their outer edges. The tributaries, however, are sliding on the ground, implying a relationship between ice motion at the coast and motion along the tributaries inland.
“That’s critical knowledge for predicting future sea level rise,” said Thomas Wagner, NASA’s cryospheric program scientist. “It means that if we lose ice at the coasts from the warming ocean, we open the tap to massive amounts of ice in the interior.”
Image courtesy Eric Rignot, NASA Jet Propulsion Laboratory and University of California Irvine. Caption by Holli Riebeek.
A slab of ice larger than the continental United States smothers much of East Antarctica. Draining from the East Antarctic Ice Sheet is a river of ice nearly 800 kilometers long. This stream, the Recovery Ice Stream, slides roughly 35 billion tons of ice into the ocean each year.
The image above depicts the region of West Antarctica where scientists measured ice speed. The fast-moving central ice streams are shown in red. Slower tributaries feeding the ice streams are shown in blue. Green areas depict
slow-moving, stable areas. Thick black lines depict the areas that collect snowfall to feed their respective ice streams.