Posts Tagged ‘bubbles’

Repost: Cracks and Bubbles

February 8, 2011

Original post, called in on January 13, 2011. Thanks once again to Jonathan Beall for the transcription!

“Hi. Today was a quiet day. Well, in terms of activity. It was a quiet day in terms of activity because it was a noisy day in terms of wind. We had a good day of spirited scientific discussions in the tent instead. We were mostly discussing bubbles and their contribution to the amount of light reflected from ice, or its albedo.

Bubbles are awesome.

Ice is very transparent. Light can travel a long way before it gets absorbed. If there are no bubbles in the ice, most light will just travel straight through, and the albedo will be low. If there are bubbles, though, light can hit the bubbles and bounce away in a different direction. A lot of the light that goes into the ice will end up bouncing right back out, which is why bubbly ice has a higher albedo than clear ice. Ice in glaciers and on ice sheets, like where we are, has lots of bubbles because it’s formed from compressed snow. The spaces between snowflakes at the surface will turn into bubbles as the snow is squeezed into ice and a small amount of the air remains behind as bubbles form.



Complex bubble shapes are partly a result of the complex shapes in the snow crystals that formed them.

We also talked about cracks in the ice, which can increase the albedo just like bubbles do. The blue ice here has lots of cracks in it, mostly quite thin. We think they form partly because the ice is cracking as it moves, and partly because, as the top of the ice erodes away from the constant wind, the ice lower down is no longer under as much pressure, and it expands creating more cracks.

Cracks in the ice (picture taken using the Crack Box, an invention I'll explain in a later post)

We actually put on our parkas and went out to look at the ice near camp to see how the cracks behaved and to figure how we might account for them in our measurements. We probably looked a little silly lying face down on the ice and wriggling along the ice like seals, but then science is frequently a little silly; that’s one of the reasons I like it.

Another incident of science being silly.

Cheers!”

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Waiting For My Ship to Come In

February 3, 2011

The vessel is coming.

Every year, McMurdo—enormous Antarctic city that it is—uses far more supplies than it would be economical to bring down by plane. So once a year, at the end of the season when the sea ice is a bit more navigable, ships come in bearing fuel and other necessities. Food, materials, parts, T-shirts for the store, you name it. An icebreaker (the Oden, this year) makes a path for the resupply ships through the remaining sea ice near shore.

This is an enormous undertaking. The fuel tanker arrived a few days ago, shortly after we got back from the field, and the fuelies (e.g. the people tasked with moving fuel around and getting it where it’s needed) have been working long hours all week to get it offloaded.



The enormous fuel tanker looks into the midnight sun. Scott's hut is visible behind it, a little ways to the right of the No Smoking sign.

Tomorrow, or so I am given to understand, The Vessel is due to come in. I don’t know much about The Vessel (as it is universally known) except that it will be taking many of our ice cores back to the States, but I do know what effects it’s having on the town. Dozens (hundreds?) of temporary helpers from the U.S. Navy have arrived to help offload it. The town’s supply staff will be working practically nonstop. Some of the inessential functions of the station are essentially shut down for the week to ensure that everyone concentrates on the enormous task at hand. Big areas of the station are restricted or entirely off limits.

In the meantime, we’re still busy processing all our samples to get them onto the vessel (we cut up the ice cores in record time, actually) and making pictures of bubbles–which I ought to post about soon.

Bubbles!

Oh, by the way, the resupply ships dock at a pier that is made largely of ice—it’s just seawater pumped into the shape of a pier during the colder parts of the season, with a little bit of a framework (I think) to help it keep its shape. It’s several meters thick. Here they are blasting the edge off of it to get it ready for the tanker, which is visible in the background.

BOOM