Research Updates

From a Distance: the AMIGOSberg and A22A Stations Send Data Back to Civilization
3 April, 2006

The IceTrek team returned to their various homes after an intensive field expedition (see Mission Log for more details). Principal Investigator Ted Scambos writes this update on the expedition wrap-up and the current status of the floating Antarctic iceberg science stations.

Even on the commercial flight back, the Icetrek team witnessed some amazing scenes related to climate change and the icy parts of the world. Relatively clear skies over southern Patagonia allowed me to get a couple of pictures of two very famous and active glaciers that flow into western Argentina: Perito Moreno Glacier and Uppsala Glacier. You may recall that the team visited Perito Moreno (see the 4 February entry in the Mission Log).

Figure 1 documents the aftermath of an event that occurred March 13, 2006: the breakdown of the ice dam on Perito Moreno Glacier that had previously separated Lago Argentino into two portions. This caused the lake levels to drop on the southern portion of the lake (right side Figure 1) as it flowed into, and filled, the northern side (left side of Figure 1). Uppsala Glacier is retreating and its ice flows rapidly, as image mapping from Landsat and ASTER satellite images have shown. The image from the airplane shows the ice has retreated about 1 km since 2001 (see Figure 2). Pedro Skvarca will continue to research the changes in both glaciers.

As for the two auto-camera AMIGOS stations, one on AMIGOSberg and one on iceberg A22A, they are functioning well and collecting images daily. Visit the station camera images site. An image of the A22A tower for April 3 is shown in Figure 3; the IceTrek team deployed a separate camera opposite the main tower so that we can monitor the state of the tower as the iceberg drifts north and begins to break down. Solar panels supply energy to the tower and can be seen as dark rectangles in the image.

The A22A setup had an extra instrument attached, a radio-echo-sounder for measuring ice thickness. The device is very simple in concept: 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--if we're lucky.

A typical radar profile from A22A is shown in Figure 4. Unfortunately, the metal structure of the tower may be causing some problems, creating a lot of reflections in the early pulse. The return pulse from the base of the ice may actually be obscured by the loud direct pulse. The earlier test on the Chip/Tempanito ice-berg is shown for comparison (Figure 5); at Chip, there were no large metal structures around. We're planning to analyze the radio pulses from A22A extensively to determine if the data can be filtered and made useable.

Figure 1. Image of Lago Argentino and Perito Moreno, previously split into two separate bodies, now one body of water following the breakdown of an ice dam on March 13, 2006.	Figure 2. Image of Uppsala Glacier from plane, showing 1 km in retreat since 2001.
Figure 3. Image of A22A tower taken by separate nearby camera.
Figure 4. A22A radar profile showing disturbance, possibly from the metal tower itself.	Figure 5. Comparison image of Chip/Tempanito iceberg radar profile, showing no disturbance. The IceTrek team did not deploy a station on Chip/Tempanito, so this profile was taken during their reconnaissance mission.

"Chip" and AMIGOSberg Deployments: What We've Learned so Far
10 March, 2006

Following successful missions to both the "Chip," or "Tempanito," iceberg and AMIGOSberg (see Mission Logs for more information), Principal Investigator Ted Scambos sent this message with an update on the research the team has conducted, so far, and how it fits in with current scientific understanding of icebergs.

On-the-Ground Research
I would like to explain in a bit more detail what kind of things we are seeing on the icebergs and what we hope to learn from them. With Tempanito and AMIGOSberg visits under our belt, we have a lot of observations that allow us to build up some ideas that we can continue to test with the satellite and on-site AMIGOS stations.

AMIGOS is an acronym; it stands for Automated Met-Ice-Geophysics Observing Station. The idea is that these stations can supplement our satellite data with high-resolution, continuous observations of various parameters on ice sheets, glaciers, and icebergs. In this case, we're setting up two stations (AMIGOSberg, which is done, and A22A, which we hope to attempt soon).

But in addition to the data that the stations will take, this expedition gives us the opportunity to do on-the-ground research. In the flights we take to the bergs and back and in our time hiking around on the surface, we're making a lot of observations of the ice, trying to figure out what is going on and how it might relate to global warming on ice shelves and ice sheets.

Seeing History in Layers
We can tell a lot about the history of the ice in the iceberg by looking at the edge (see Figure 1). Layering shows us the yearly history of snowfall; but in warm summers, this snow melts, leaving blue layers of refrozen ice. This formation of melt on the surface is thought to be a big part of the process of ice shelf disintegration. We can see that AMIGOSberg, which came from the southern Larsen C (about 450km to the south of where we met up with it), seems to show an increase in the intensity of melting in the past few years.

The last year or two would be after the berg broke free, and drifted north. But the top 8 meters of the berg represent about the last 15 years of time. The face is about 25 meters tall, so we can look back in time by looking at the layers in the ice. The layers give us an indication that climate is warming well to the south on the Peninsula.

Warping of an Iceberg
We also wanted to look at the structure of the edge of the iceberg. Models predict, and satellite measurements show, that the iceberg edge is flexed. In cold water, the main force is a downward bending of the ice. It's a subtle effect, but think of it as the same kind of force you get on the top of a cork that is pushed halfway into a bottle. The force of buoyancy is 'squeezing' the submerged sides of the ice, warping the iceberg. This effect is so subtle, you really have to be at the edge, looking at it in comparison to the water horizon, to see it. And, ideally, you would have to measure it with GPS.

On AMIGOSberg, we didn't have time to do a precise GPS profile, but we used the line of flags that we were
setting out, as we walked, as a guide to measure the structure of the iceberg. As flags disappeared or reappeared behind us in our line of vision, we knew we were going up or down. We found that AMIGOSberg is flexed like a cork, humped with a downward slope of as much as 10 meters--more than we measured with the satellite. See Figure 2; note that the berg edge is sloped over Ted's left shoulder, but the waterline is flat in the other small berg in the distance.

On the other hand, in warmer water (by that I mean without sea ice on the surface--the water is still darned cold!) another effect takes over, and the edge profile is sloping upward. We're expecting to eventually see this on A22A, the edges of which are currently sticking out from the iceberg. What happens in warm water is that wave action erodes the waterline rapidly, and the top part of the berg breaks away. But below the surface, the erosion is not so fast, and so there is a kind of 'bench' formed in the ice. This 'bench' wants to float up, and so it lifts the ice at the edge upward. We got a great photograph of an iceberg that shows this process (Figure 3). It has recently tilted, showing what used to be underwater.

The other thing you'll notice is that the top of that small tilted iceberg is covered in cracks. This seems to happen to all the small icebergs that make it to open water. We currently think that this may be the the effect of the very gentle ocean swell that begins to appear near the boundary of where sea ice occurs. We think the swell is flexing these icebergs. But south of the boundary of where sea ice occurs, there is no ocean swell. Thee, it's always calm water because the sea ice on the surface of the water absorbs the ocean's wave energy by bumping into each other.

Push and Pull of the Tides
One last thing we're looking at is how icebergs drift, and what forces are pushing them around. In a word: it's tides! This was a surprise to scientists until a few years ago. Most scientists previously thought that a combination of winds and currents push the icebergs. However, it turns out that iceberg motion is a bit like having a ball on a flat board, and then tilting the board around. The tilting represents the coming and going of the Earth's tides, resulting in a very very gentle slope on the ocean--a slope on the order of only 1 meter height in 1,000 km. The icebergs simply slide "down-hill." Currents and winds have a secondary, smaller effect.

In the last picture, we've plotted the first 76 hours of iceberg motion on a zoomed satellite image of AMIGOSberg (Figure 4). The GPS sensor, located on the tower, is at the site labeled 'acamp' on the image at the time of the photograph. From the motion, shown with a thin line, we can see that the motion "loops" and shows a pattern caused by tides.

So, even though our Mission Log entries may make it sound like we're merely constructing towers to take data that we'll analyze later on, each of our outings during the expedition provides us with crucial on-the-ground observational research. This hands-on research helps us add to the current scientific understanding of how icebergs work.

Figure 1. Layering shows the yearly history of snowfall. In warm summers, the snow melts, leaving blue layers of refrozen ice. Photograph courtesy Marcelo Gurruchaga.	Figure 2. The iceberg edge is sloped over Ted's left shoulder, but the waterline is flat in the other small iceberg in the distance. This slope shows that the iceberg is being flexed by the forces around it.
Figure 3. Warmer water washes against the iceberg and causes benches to form. The benches push the iceberg edges upwards; here, a bench floats above the water line and forces ice that used to be underwater into view.	Figure 4. This satellite image shows the first 76 hours of AMIGOSberg's motion after we deployed the GPS and weather station. The GPS, which is sending back data on the iceberg's current position, is located at "acamp." The thin line indicates where the GPS station, in its fixed position on the iceberg, has moved because of tidal forces.