IceTrek A22A Deployment: 7 March - 19 March
Please credit the National Snow and Ice Data Center for image or content use.
The field team awoke in camp on A22A at 4:30 a.m. and continued to assemble the tower and dig the foundation. By the scheduled first communications of March 19, at 6 a.m., the team had the 7 m tower upright and guyed out. By 8 a.m. the tower had the additional truss system (for extra support under possible softer conditions late in the life of the iceberg). Over the next several hours, the group dug 50 m of trench for the radar system cables and collected and measured an 11 m ice core. A snow pit showed ice layers from the just-finished summer, and coarse gravel snow somewhat like the "Chip" or "Tempanito" iceberg that the IceTrek team visited in February.
Rob describes the field team's efforts:
"We got up at 4:30, in the dark, and started assembling the tower using our headlamps for illumination until sunrise. We worked straight through to 5 p.m., with a break every two hours to contact the ship via radio and talk to Ted, who remained onboard to coordinate communications. During our breaks, we also drank hot tea to help keep us warm. The wind continued at 30 knots and made working just that much harder. We finalized instrument settings, completed an ice core, and set out 1.2 km of flags towards the edge of the iceberg.
The scenery was stark, yet had a unique beauty. We had been under a cloud most of the night and the next day, but late in the afternoon, the sun broke through and the scenery was breathtaking. We caught occasional glimpses of the ship as it navigated around the iceberg. Around 3 p.m., a group from the Irizar did a flyby photo shoot onboard a Sea King helo. They didn't touch down, as it was deemed a bit hazardous, but it was good to see the helo as it clattered by.
Shortly thereafter, the helo returned to pick us up and return us to the ship. So, a full day's work, and well worth it!"
The group is safely back aboard the ship and resting after their cold day of work. Ted is pleased with the outcome of the deployment, saying, "The cameras are functioning well, and the first image from the netcam is a spectacular shot of the sunset only 10 minutes or so after the field team boarded the helicopter and swept back to the ship."
The IceTrek team flew a reconnaissance survey over A22A's edge and interior, today, before deploying the crew on the iceberg. Ted, Rob, Ronald, Juan Carlos, and Dr. Yevgeny Yermoling, a snow and permafrost scientist from the Dirección Nacional del Antártico, arrived on the iceberg at 5:40 pm.
Ted reports, "It was fairly windy, about -4 degrees C, with heavy low clouds at the time of put-in. However the surface was firm and definition was adequate for landing." Ted helped establish the orientation and layout of the site, then returned to the ship to work communications and satellite images.
The rest of the field party remained on the iceberg and managed to assemble the tower and connect the main camera. They set set up camp and turned in at 9 p.m.
Rob writes, " As it was getting dark, we set up our two tents and and crowded into the larger tent to drink tea and eat a little dinner. Just before settling in for the night, we made a few short satellite phone calls to say we'd arrived. Temperatures were pretty warm during the night, around 9 F, but the wind was rapidly building to around 30 knots."
The IceTrek team continues to prepare for their deployment to iceberg A22A. They are also analyzing some of the on-the-ground research they have been completing over the entire mission for the first of our Research Updates.
We have a lot of observations that allow us to develop some ideas that we can continue to test with the satellite and on-site AMIGOS stations. AMIGOS is actually an acronym that stands for "Automated Met-Ice-Geophysics Observing Station." 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 (well, we hope there will be two).
But during the flights we take to and from the icebergs, and in our time hiking around on the surface, we're also 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.
We can tell a lot about the history of the ice in the iceberg by looking at the edge—you can see this in the above photograph. Layering shows us the yearly history of snowfall. During warm summers, this snow melts and forms 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.
AMIGOSberg came from the southern Larsen C Ice Shelf, (about 450 kilometers to the south of where we met up with it). It shows an increase in the intensity of melting in the past few years. Now, the last year or two would be after the berg broke free and drifted north. But the top eight meters of the berg represent about the last 15 years of time—and the face is about 25 meters tall. So we have an indication that climate is warming well to the south on the Antarctic Peninsula.
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. Cold water forces 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 and warping it. 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, or you can 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 a guide to measure the structure. As flags disappeared behind us, or reappeared, we knew we were going up or down. We found that AMIGOSberg is flexed like a cork, with a downward slope of as much as 10 meters—more than we measured with the satellite.
On the other hand, in warmer water (by that I mean without sea ice on the surface—it's still extremely cold!) another effect takes over, and the iceberg edges slope upward. We're expecting to see this on A22A, which is sticking out from the edge of the sea ice now. In warm water, wave action erodes the waterline rapidly, and the top part of the berg breaks away. Below the surface, however, the erosion is slower, and this forms a "bench" in the ice. This "bench" wants to float up, and so it lifts the ice edge upward.
The other thing you'll notice is that the top of that small tilted berg in the photograph above is covered in cracks. Right now, our theory is that the very gentle ocean swell that begins near the sea ice edge is flexing these icebergs once they make it to open water. While the icebergs are drifting in the sea ice, south of the ice edge, there is no ocean swell. The water there is always calm, because the ice bumping around on the surface absorbs the ocean's wave energy.
One last thing we're looking at is how icebergs drift, and what forces are pushing them around. It's tides! That may be a surprise to you; it was to us until a few years ago. Most scientists thought that a combination of winds and currents pushed the icebergs, but 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 gentle slope (on the order of 1 meter of height in 1000 kilometers) on the ocean surface. The berg is simply sliding downhill. Currents and winds have a secondary, smaller effect. In the zoomed satellite image above, we've plotted the first 76 hours of iceberg motion of AMIGOSberg. The GPS sensor is located on the tower, which was at the site labelled "acamp" on the image at the time of the picture.
The IceTrek team is still recovering from their overnight deployment on AMIGOSberg (see Mid-Size Deployment, AMIGOSberg) and planning for their upcoming expedition to iceberg A22A. Rob writes, "The Irizar is 8 nautical miles southeast of Marambio Station. We need to offload about 70 people and pick up about 80 others for transfer to Esperanza, but the weather is bad, again, so the helo crews aren't making any flights. We are hoping to make it to A22A early next week."
On another note, the NASA Earth Observatory news site is featuring the IceTrek expedition; visit IceTrek Expedition to AMIGOSberg.