Fieldwork for exposure dating is very rigorous. The first day we ventured into the field, I thought I had woken up to find myself enrolled in Antarctic bootcamp. Over a span of about nine hours, John, Perry, and I walked about eight miles. We were only a total distance of 2.3 miles as the crow flies, but while looking for samples, we zigzagged back and forth along the margins of the moraine. A moraine is a very haphazard assemblage of rocks and sediments. The rocks range in size from pebbles to car-sized boulders. They are randomly scattered and form a wide range of hummocky landforms. We walked out to the edge of the plateau and part way up the mountain.
Before going out into the field, the first thing John does on a daily basis, is to read the digital barometer. This allows him to calibrate elevations. Elevation readings fluctuate with the weather. If a low pressure system moves into the area, the apparent elevation increases; conversely, if a high pressure system comes through, the apparent elevation decreases. In Antarctica, air pressure readings are often anomalous (this is also due to the atmosphere being thinner around the Earth's poles than around the equator). This is a field practice that is more of a remnant from earlier field days when the accuracy of GPS readings available to the general public were very general. (GPS satellites were originally developed for defense purposes and unless accessed by the military, the average user could only pinpoint their location to within tens of meters.) Today, GPS locations are generally accurate to within a meter or so for your ground location and within a couple of meters for elevation. John is still reluctant to rely solely on GPS data and prefers to double check his data collection by using the barometer.
Prior to heading out into the field, the digital barometer reading must be recorded. Here, John is instructing Perry on how to record information from the digital barometer.
Some of the best samples are cobbles found perched on boulders. An ideal sample in this region would be a quartzite or a siliceous limestone (limestone with lots of quartz running throughout). In addition to being the correct rock type, the sample must also have the correct amount of weathering (not too much), exhibit evidence of glacial transport (striations - or grooves where it scraped against bedrock during transport), and if not perched on a rock, sitting on the surface of the ground and none of its surface buried. For the sample to be useful for dating the Last Glacial Maximum (LGM), it must be located near the margins of the glacial boundary. If the sample if located too deeply within the moraine, it may not be in its original position, having slumped or settled down into a hummock as the moraine becomes compacted over time. This would cause it to give an inaccurate date because cosmic rays would not be bombarding the same surface consistently. If the sample is too far outside the LGM limits (edge), then its membership to the LGM becomes suspect.
Searching for sample: John and Perry inspect cobbles perched on a boulder to determine if any are worth collecting.
While three pair of eyes are better than only one pair, I often felt inadequate while searching for samples. It seemed like every potential sample I found was lacking just one of the criteria. Either it was the wrong rock type but had the correct amount of weathering and glacial striations, or it was the right rock type with correct weathering, but didn't have enough glacial striations, or something along those lines. I was growing frustated with myself for not being able to find a sample and had to remind myself that John has been collecting samples for almost 20 years here in Antarctica. He's a pioneer in this field and he has learned what makes a good sample from years of experience. Also, Perry was expressing frustration, and John said that this is one of the more difficult locations to sample that he's ever been in. The limits of the LGM are very poorly defined in this location.
Finally, we found our first sample! John has appointed me the "Minister of Field Photography". It is my responsibility to take photographs of the sample in situ (in the place it is found) and photos of the terrain around the sample. In addition to these photos, I also take a photo using a fisheye lens. This photo is taken after the sample has been described and collected. The camera is placed on a beanbag located exactly where the rock once was. It is then leveled so that it is pointed straight up at the sky. The fisheye lens enables the picture to capture the entire horizon around the camera. John uses these photos to correct for any fluctuations in cosmic rays striking the sample.
Our first sample of the season - it is in situ (its original location). The sample bag is folded up next to it with the sample number written across the bag. The sample is numbered: 10-BDM-001-CMK. The 10 stands for the year (2010), BDM indicates the funded project name - Beardmore [glacier], 001 is the sample number, and CMK is the location - on the side of Cloudmaker Peak. As we move to new locations throughout the field season, the numbering will change accordingly, but still use the same format. For example, samples collected on Mt. Hope will probably be labeled: 11-BDM-086-HPE.