IceTrek tracked the life cycle of wandering icebergs to learn about collapsing ice shelves
Posted August 22, 2008
Despite the rapid warming under way along the Antarctic Peninsula, it’s not every day that an ice shelf disintegrates. For scientists like Ted Scambos who want to learn more about how these giant floating cubes of ice break apart, the next best thing is an iceberg.
In 2006, Scambos joined American and Argentine colleagues on an expedition dubbed IceTrek . The scientists landed on two icebergs to set up high-tech automatic weather stations that would track the bergs and collect data on their northern float to eventual oblivion.
The AMIGOS, for automated meteorology ice geophysics stations, had built-in GPS units and cameras, as well as weather instrumentation. Experiments included measuring accumulation, ablation (ice loss from vaporization) and ice motion based on images beamed back by the AMIGOS’ cameras, according to Scambos, lead scientist at Boulder, Colo.-based National Snow and Ice Data Center .
“We flew out to these icebergs and installed these things, and watched these icebergs evolve as they drifted north,” he explained two years after the expedition. “It was our first experience with installing these units. It’s a tough environment when you have a lot, a lot of melting going on to install stuff that will remain stable.”
The bergs were called uk211, which the scientists nicknamed AMIGOSberg, and A22a. The setup on A22a had an extra instrument attached, a radio-echo-sounder for measuring ice thickness. A transmitter uses a cascade release of energy from capacitors to send out a very brief, but very powerful, radio pulse at about 10 MHz wavelength. A receiver begins to listen as soon as the loud pulse is triggered. It sees first the direct pulse through the air and then the reflected pulse from the bottom of the iceberg.
“They did work,” Scambos said of the AMIGOS towers. “They worked right up until they fell off the iceberg, which is kind of what we wanted. I did think that the icebergs would get covered with melt ponds and disintegrate before this other process — which is this slow, wearing away of the edge of the iceberg — would get to them.
“With the AMIGOS it was very close. It was almost right to the very end when our station fell into the ocean and it disintegrated. With [A22a] iceberg, we were too close to the edge for how long the interior survived.” The unit on AMIGOSberg last for about eight months, just two weeks before the berg completely disintegrated. A22a held on longer, about 19 months after the team installed the AMIGOS unit, which rode the iceberg for about 10 months.
Understanding how ice shelves disintegrate is an important piece to the puzzle of calculating sea level rise. While the floating shelves don’t contribute directly to sea level rise, their disappearance uncorks the glaciers that flow into them. These rivers of ice, in addition to ice sheets, are how the oceans increase in volume.
Surface pond melting and fracturing is the classical way scientists viewed the breakup of ice shelves. But many believe that melting at the base of an ice shelf also contributes to disintegration, perhaps even carving out huge cavities in the hundreds-of-meters-thick shelves. The absence of sea ice in front of an ice shelf, which would serve as a buffer and damper ocean waves, may also play a significant role in a disintegration event.
“The most important thing [from the project] was a strong confirmation that the surface melt water breakup process is one of the ways that ice shelves [disintegrate],” Scambos said. “That’s what I have to say now; at the time, I was saying it is the way ice shelves disintegrate, but I think the recent slew of papers, plus what’s happened to the Wilkins [Ice Shelf] during this austral winter, shows there’s more than one way.
“We’ve got a pretty good study on how icebergs collapse and as an analogue to how ice shelves disintegrate,” he added.
The Wilkins Ice Shelf on the west side of the peninsula has been disintegrating since the Southern Hemisphere summer, an event Scambos discovered in March from satellite data. During the winter, it has continued to break up.
Scambos hopes to use instruments similar to the AMIGOS for a large International Polar Year project to the Larsen C ice shelf on the other side of the peninsula. The LARISSA (LARsen Ice Shelf System Antarctica) project will pull together scientists from numerous disciplines to study the Larsen ecosystem, site of two previous shelf breakups. The science cruise is scheduled for the 2009-10 field season.