So, what are we actually doing in Antarctica? Why have we come to the bottom of the world? The short answer is that Antarctica plays a large role in controlling the Earth’s climate and global sea level. Geologists often say that the present is the key to the past. For example, by studying modern glaciers and ice sheets one can learn to recognize glacial deposits in the geologic record. Using these deposits, as well as many other types of sediments and a host of geochemical techniques, we can reconstruct past climates, and thereby learn something about what the future might hold. We are especially interested in what Antarctica was like during periods that were warmer than present. Did the ice sheet shrink or collapse raising sea level, or did it grow larger, drawing down sea level?
The mountains in the Dry Valleys of Antarctica, about 50 miles across McMurdo Sound from the US base on Ross Island, contain glacial deposits dating back to the initial growth of the Antarctic ice sheet over 15 million years ago. The deposits record the presence of wet-based alpine glaciers, that slid along their base during a warmer climate. They probably looked similar to those presently in the Himalayas. At some point, the climate cooled resulting in the cold-based polar glaciers of today that are frozen to their base, and flow only by internal deformation. Determining when this occurred, is one of the goals of our research.
There are also spectacular erosional features consisting of channels and potholes cut into sandstone bedrock that look like they were cut by torrents of water. However, these features occur along the highest ridges rather than the valley bottoms where you would expect to find them. This has lead to the idea that they were carved under a glacier. But to get a glacier to these heights would require the Antarctic ice sheet to thicken by thousands of feet to flow over the tops of the mountains. In contrast, during the last ice age, the ice sheet only thickened several hundred feet and did not even flow through the Dry Valleys.
Yet, these features are clearly slowly eroding today. Could they be the result of millions of years of grain by grain erosion of the sandstone? The winds are certainly strong enough to blow the loosened sand away. These are the hypotheses that we are going to test by measuring the cosmogenic nuclides in the rock. This technique will be explained in another blog, but suffice to say that we can determine the age and erosion rates of samples we collect and bring back to the lab at Harvard. If erosion rates are low, and similar everywhere it will favor the subglacial hypothesis. If erosion rates are much higher in the bottoms of potholes and channels than in the surrounding rock it will favor long erosion by wind and freeze thaw mechanisms.
Well, all our gear is packed (just over 2100 lbs) and on the way to the helo pad. Tomorrow, weather permitting, we will use two helicopters (or two trips) to ferry all this stuff and ourselves to our first camp, about 45 minutes (100 miles) away. We have to get the stuff down there the day before now. We used to just bring it down when they were ready to load the helo, but now they often use sling loads, and I guess they need time to build them up. Just another example of the increasing bureaucracy down here. It always seems to make things easier for the support staff rather the scientists, but I guess I can’t complain, and if I didn’t know how it used to be I would not think it so bad. All things considered the field support is really terrific.
For example, Rob and I went out for the day by helicopter to our first field area, the giant potholes of the western Asgard Range, on Wednesday while Allen and Jenny were at snow school. Marianne, a support person from the GPS group (UNAVCO) came with us to make a LIDAR map. This instrument uses a laser beam to make a 3-D map, of an ~ ¼ square mile area with a resolution of an inch or two! We can use the data to make an old fashioned contour map or generate views from different points. We can also analyze roughness and slope angles, and eventually will have an interactive map you can “walk” through like a video game and examine our sample sites! Very cool, and not something you could do only a few years ago.
The weather was really fine, light winds and temperatures of 10-15° F, hopefully the weather will hold. A highlight for me was I got to ride in the co-pilot seat on the way out, something I had never done in a “Huey” helicopter in all my previous trips. Generally, a helo tech, or crewman sits there. Back when the US Navy flew the Helo’s there would be a co-pilot and a crewman in the back. But we were flying with the New Zealand helicopter that has only one pilot, and I needed a headset to guide him into our site. We flew with one of the USAP helicopter on way back was more more typical, jammed in the back with a lot of gear.
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