Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
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Using an ice auger to drill into sea ice to measure thickness.

  (Click for a larger image)

Lessons on Sea Ice, p2

by Mary K. Miller

The best way to avoid such mishaps is to drill down into the ice until you hit water and to measure the thickness. Depending on its weight, each vehicle needs a certain thickness of ice to safely drive over. With our classroom lesson over, we hopped in a big track vehicle called a Nodwell (this one was named "Uncle Buck.") and drove out of town. After a few miles of deafening, bone-chattering transport in Uncle Buck, we stopped for a hands-on lesson in measuring the thickness of sea ice using a hand-cranked auger. It takes several minutes to finish the drilling before we found out that the sea ice is over 3 meters (9 feet) thick, plenty thick enough for Uncle Buck to drive over.

It turns out that the sea ice is thicker over McMurdo Sound this year than in recent history. The reason lies in an event that happened in March 2000. That’s when a huge iceberg, named B-15, broke off the Ross Ice Shelf 200 miles east of McMurdo station When it calved off, B-15 was the size of Jamaica and extended 900 feet below the surface. . Why it broke off is still under debate but some scientists think that it may be related to global warming.

Whatever the mechanism, B-15 is one of the largest icebergs in recorded history and it soon went floating toward McMurdo. The giant berg eventually crashed into Ross Island not far from McMurdo Station. The berg is so massive that it blocked currents moving into the sound, turning the sea into what Ted described as a giant millpond. Ice started forming behind B-15, covering the sea from Ross Island to the Drygalski Ice Tongue to the east.

The sea ice grew so thick that it never melted last summer around McMurdo Sound and it looks like it’s also here to stay this year. That’s great for vehicles and people to travel over the ice, but not so good for the wildlife. For instance, Adelie penguins normally breed and raise chicks in rookeries along what would be a coastline in the summer. The Adelies depend on getting into the water to fish and feed their young. The ice edge is now 73 miles away, a long walk for a penguin. By the time they arrived this year from the open sea to the rookeries, usually sometime in November, they were already exhausted. It shows: from some early surveys this year, scientists have seen a dramatic decline in the numbers of breeding penguins. We’ll be going out to take a look at an Adelie rookery for ourselves later this month.

The U.S. Coast Guard will also have to contend with the ice in late December. That’s when a couple of icebreakers will cut a channel in the ice to clear the way for Greenwave, the huge ship that carries all the supplies for McMurdo station for the next year. Normally the Coast Guard only needs one icebreaker but with 73 miles of ice to cut through, they’re bringing out two this year. People have been laying odds on how long it will take them to get through to McMurdo, always a big event here on the station.

links:

Ice Gallery (requires Flash 5 player).

Satellite images of icebergs and sea ice: 1, 2

Iceberg Movies

     
 
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