Images of

ANTARCTICA

Gravity Measurements

Photos © 2002 Seth White

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When I gave notice at my old job that I was headed to Antarctica, Gunnar Recht came by my office with this book: Innocents on the Ice, by John Behrendt. It was a fascinating story of his experience in Antarctica as a young man during the IGY (1957-58). He wintered at Ellsworth Station under the notorious captain Finn Ronne, then went on a traverse the following summer over a heavily crevassed area. His book contains excerpts from his diary, combined with his commentary as an older man. Absolutely great reading. So this was my first literary experience of Antarctica, and it gave me a great picture of what it was like here (at least in the old days). As it turns out, he came to the ice this year aboard the Nathaniel B. Palmer (research icebreaker) and was in McMurdo for a few days. I stumbled upon him in the coffee house, and started up a conversation. Along with some good stories, he told me he was going to do some gravity measurements at the ice pier as a favor to another science group while he was on station. Problem was, although he'd driven just about every single Antarctic vehicle ever invented, he hadn't had the mandatory briefing on how to operate the current pickup trucks. This briefing doesn't take long, but he only had one more day here and was slated to give a presentation to the station on his experiences. So, since I have a dedicated truck as part of my job, I offered to drive him and his colleague around station so they could do their measurements as rapidly as possible. So the next day, we headed out to take a gravity survey of the ice pier. Not every day you get to ride around with an OAE (Old Antarctic Explorer) doing scientific measurements! His presentation was excellent too - it's unbelievable the kind of stories that he has from the early days of the US work here, when the Navy was in charge. Here is John, after his presentation in the galley. Many people at McMurdo say they have the best job on station (which is a remarkable and telling fact!). But it's got to be pretty hard to beat the science tech job....I'm lucky to be here.

This is an old pump house, which was converted to act as a gravity base station. This is a location where the gravity is very well known, and it serves as a calibration point for gravity measurements.
This station is a Thiel gravity base station, as noted by this marker. It is named after Ed Thiel, who was John's supervisor during his first expedition here. Ed was killed in a plane crash a couple years later on another Antarctic trip. John speaks very highly of Ed.
This is the base station itself: a concrete block mounted directly to the earth.
There's a little marker in the center of the concrete block to mark the exact point.
Here's John reading his gravimeter. At left is Brian Welch, who had just returned from this year's leg of the ITASE (International Trans-Antarctic Scientific Expedition). He was doing deep radar measurements of the earth below the ice sheets during the traverse, and came along to record GPS info at each of the gravity survey points before flying back home.
After obtaining the reading at the base station, we went to the ice pier. This is a picture of the edge of the ice pier, looking outward into McMurdo Sound. The pier is, as its name implies, a block of ice which floats next to the ship for loading purposes. It is covered with soil for several reasons, one of which is insulation to keep it from melting.
A hut constructed on the ice pier, with my pickup truck nearby.
Another pic of the hut. They were drilling on the pier that day for some reason, but it didn't seem to affect our measurements much.
John and Brian doing a measurement at one of the seven posts on the pier.
Taking a reading at Post 1. The gravimeter is a very sensitive spring-mass system (with a quartz coil spring used for thermal stability considerations!) which is used to measure the earth's gravitational field at a certain point. Gravity will vary slightly from place to place due to the varying distribution of mass in the earth below. This particular sensor costs about $15,000.
Brian and John again, taking another reading at Post 2. The Nathaniel B. Palmer has a gravimeter on board, and the marine science tech (my counterpart on the ship) is taking gravity readings during its cruise down here. When it arrives, they will want to check for drift in the measurement system, and thus an accurate reading of the gravity at the ice pier was requested so they would have a convenient point to reference against the ship's sensor.
Another reading. The measurement at the base station was dead simple, since it was a stationary point. However on the ice pier, the subtle motions due to the ocean were enough to cause the meter to oscillate back and forth. Thus, John's extensive experience in this sort of thing was useful to get as accurate a measurement as possible.
John again, logging the time of the measurement.
A closeup of a gravimeter reading.