Monday, December 29, 2008

WAIS - Dec 29, 2008 - Tim

Name: Tim Bartholomaus

Date: 12/29/08 (Actually 12/30/08 now that I'm off-shift and getting to
my entry)
Location: WAIS Divide Galley
Time: 14:00 am
Latitude: 79° 28’ 1.2” S
Longitude: 112° 5’ 6.0” W
Elevation: 1,759 m
Borehole depth: 850 m
Temperature: -19 °C (-2.2 °F)
Wind speed: 7.5 km/h (4.5 mp/h)
Visibility: 400 m
Clouds: broken, fog
Wind direction: 260 degrees (out of the west)
Barometric Pressure: 28.93 in Hg
Precipitation: none
Breakfast (actually lunch at camp, noon): Turkey with cranberry sauce, beets, stuffing, sweet potatos
Lunch: (actually dinner at camp, 6 pm): Lamb, with mash gravy, fries, veggie and feta patty with curry sauce, fish chowder, roasted vegetables
Supper (mid-rats, midnight): "Mom's" grilled shrimp with spinach, spaghetti, grilled eggplant and rutebega.

There's a saying around Antarctica that some people like to use: "They lied about the job. I lied to get the job." Mostly, I think this sentiment is confined to some of the folks in McMurdo Station that work for Raytheon Polar Services Company, the US Antarctic Program's logistics and support contractor. Even McMurdo needs garbage collectors and dishwashers, while many people likely come south with grand visions of wide-roaming explorations similar to those of the "heroic age" of exploration.

I would not say that the "lies" saying holds true for any of our core handling crew. In fact, one of the questions on the job application was to the effect of "What experience do you have working long days at -20 degrees C?" It's an honest question, and I think we must have all responded honestly. Everyone seems to be holding up well to the conditions. When I interviewed for this core-handling job, it was described to me as very cold, very loud factory work. This is mostly accurate, although it's not as loud as it could be- for one, I don't need to wear hearing protection unless I'm working right next to one of the four very large refrigeration units that maintain the temperature of our working space between -25 and -30 degrees C (-13 to -22 deg F). However, unlike most factory or assembly line workers, one of our main goals is to handle our product (ice core) as little as possible because it is so brittle (see Logan's 12/17 or Bess's 12/22 entries). Our work on the "factory floor" comes after that of the drillers (who, incidentally, work in a warmer, quieter environment). Once the drillers produce the ice core and pass it to us, our responsibilities, in order of priority, include:

1) Protect the quality of the core so that chemical measurements can be later be made of the ice, trapped air, and dust brought up in the core. This includes keeping the ice cold so that trapped air does not diffuse out of the core, and not inducing any more fractures than are already present within the core.
2) Maintain the top-bottom orientation of each piece of core and its position within the 3,500 m-long (2.2 mile-long) entire ice core.
3) Make preliminary (but as accurate as possible) measurements of the length of each piece of core and any breaks or fractures within each core, so we know from what depth the ice came.
4) Store the ice core in a way that responsibility (1) is met.

Many of the blog entries thus far have discussed camp life, particularly the things that make us most happy: interesting people, beautiful landscapes, good food, fresh food, mail, airplanes, skiing, shenanigans, etc. However, a few people have asked me about what it is that I actually do for work. So, I'm going to tell you a little bit about the steps we take to meet the four priorities outlined above.

The core comes up in the drilling arch (as you might guess: a building shaped like an arch), which is separated from the core processing arch by a thin wall. Once the core barrel is rotated to horizontal, the drillers manually push the core out of the core barrel, from the drilling side to the core processing side, with what looks like a round sponge on a long stick. On the processing side, the core slide into green plastic netting that protects it and helps keep it intact in the event of cracks or spalls off the surface of the ice (on today's shift, we probably had an average of 5 fractures per meter of core).

As soon as we get the core, we measure the lengths of each of the three pieces of core the drillers give us with a slick little device known as a Balluff. The Balluff slides on a rail parallel to and above the core, shines a laser line across the diameter of the ice cylinder, and digitally reads out its position on the rail to the nearest millimeter. A button allows us to reset the Balluff position to zero, thereby allowing us to quickly measure the length of each piece of ice and note the positions of anything interesting (score marks, fractures) along the length of the ice. At this first station, we also count the fractures in the ice, measure the temperature of the ice (typically -31 deg C, mean annual air temperature at WAIS Divide) and of our work space (generally around -27 deg C), draw arrows on the ice surface to indicate the original up direction of the ice (we use pencil), and note the quality of the ice core. As soon as possible, we give our notes to the drillers, so they have feedback and can make any adjustments to their drilling technique, as necessary. From this first station, we slide the core in a 4-meter-long, aluminum tray over to another station that is similarly equipped with a Balluff.

At this second station, we re-measure the core as a double-check, note the type and positions of any fractures, draw hatch-marks across fractures (in case the core falls apart later and needs to be reconstructed), and put identifying marks at set depths on each fragment of ice. From the computer on which we log all of this information, we print a "birth certificate" that contains all of this information and that will travel and live with this ice core for the rest of its "life." From there the core is slid into 1.1-meter, stackable aluminum trays and put on wheeled rack carts. At this point, the core-handler's job is done and the core is passed to those responsible for measuring the electrical (properly, dielectric) properties of the ice.

The head scientist at WAIS Divide, Ken Taylor, has a machine (operated by Natalie and John) that can measure these electrical properties at roughly millimeter resolution along the length of the core. The dielectric properties (DEP) of the ice vary with the concentration of ions, or salts, within the core. It turns out that the salt concentration of snow varies with the season, with maxima each summer. These peaks in concentration are preserved as the snow turns into ice; therefore, each peak measured at the DEP machine corresponds to one year. The DEP machine therefore allows us to quickly, in the field, assess the age of the ice we've pulled up. Just yesterday we logged ice that was on the ice sheet surface, as snow, 3,500 years ago! Maybe one of our readers can shoot us an e-mail with what was happening in the world 3,500 years ago. Unfortunately, we scientists are at something of a loss on our ancient history.

So, that's what's happening on the "factory floor" here at WAIS Divide, 24 hours a day, 6 days a week, for about another 3.5 weeks. As you might suspect, it's more complicated than it sounds, with the complications largely centering on how one measures the length of a roughly, irregularly fractured length of ice core. But that can rest for another blog entry.

-Tim

1 comment:

Tim's Mom said...

You are drawing arrows on ice older than King Tut (Tutankhamen c. 1350 BCE) and the glory and greatest extent of Egypt! That XVIII dynasty is the best-recorded period in ancient Egypt. May it be so for your ice cores. We've just entered 2009 here in NYC, crossing slowly into another year while your team whips them out meter by meter, centuries at a time. It just boggles the mind. Happy New Year to all of you doing such important work at WAIS Divide. We read every word of every blog.