Science News - March 26, 2011

Jason Box spent the summer of 2009 waiting for Greenland’s Petermann Glaciertobreakapart. Everything signaled the glacier was ready to go. Melt ponds were pooling on its surface, and massive cracks were opening on the icy tongue that stretched offshore into Baffin Bay. Box, a glaciologist at Ohio State University in Columbus, spent two months on a ship, his cameras trained on the volatile edge where ice meets ocean. He was determined to catch Petermann in the act.

As luck would have it, the glacier held out one more year. When Box wasn’t looking, on August 4, 2010, a piece of ice four times the size of Manhattan broke off. It was the largest iceberg to calve in the Arctic since 1962.

The world’s frozen places are full of glaciers like Petermann, slow-moving rivers of ice flowing into the ocean and poised on the edge between stability and collapse. In recent years, many of these volatile glaciers have spit out more and more chunks of ice to float away as icebergs and then melt. The more icebergs a glacier discharges, the faster it tends to move, thin and retreat away from the coast.

Scientists say that understanding the processes that control ice’s march to the sea, known as “ice dynamics,” is crucial for understanding the future of the planet’s great ice sheets atop Greenland and Antarctica. Were it all to melt, there’s more than enough ice there to raise sea level by 67 meters.

A complete meltdown isn’t likely, even centuries from now. But many researchers worry that Greenland and parts of Antarctica could soon contribute more to rising sea level, as temperatures are increasing fastest in those regions. And a small difference — say a foot of sea level rise, versus a meter — could mean the difference between much of Miami staying above water or going under in the next century or two.

As ice melts, water trickling through
the remaining ice affects how quickly a
glacier moves and breaks apart. To bet-
ter understand and forecast such effects,
researchers are targeting a few key out-
let glaciers, which funnel ice from the
high frozen interior into the oceans. By
peppering these glaciers with instru-
ments to measure their flow, cameras to
photograph their every move, and even
underwater submersibles to test the sur-
rounding oceans, scientists hope to learn
what drives the ice.

Slip sliding away

Because of ice dynamics, Greenland loses
as much ice each year as is contained in
the entire Alps. Within Greenland, per-
haps no glacier is more responsible for
that ice loss than Jakobshavn Isbrae, on
the island’s west coast. As glaciers go, it’s
one of the world’s fastest, with ice flowing
up to 14 kilometers per year — fast enough
that you can see it move.

How glaciers flow Glaciers are slow-moving rivers of ice, pulled downhill by gravity. If a glacier meets water, some of the ice breaks off as icebergs. In a stable glacier, this calving of icebergs is roughly in balance with snowfall. But there are several ways to speed up a glacier, as shown below.