Submitted by Anonymous on Tue, 01/01/2008 - 12:46
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SEDNA Beaufort Sea Ice

 How deep was the ice measured, and what does a stress buoy do,

Wyatt 

Sun, 01/06/2008 - 14:47

Robert Harris

Hi Wyatt,
I wanted to make sure I had the real scoop, so I contacted Dr. Geiger to make sure I had accurate information.  She wrote,
How thick was the ice?   The ice floe we set our camp on was something called a Multiyear floe. This means it was growing for several years and was about 4m or 12 ft thick. The ice that had only grown one season was about 1m or 3ft thick and this was spread all over the place. Then there were ridges which formed by two floes buckling against each other. These ridges were anywhere from 2-10m (6-30ft) in the vicinity of where we were. Ridges basically look like long narrow snowbanks but they are made of ice that has been twisted and piled both above and below the level ice we were standing on with anywhere from 2/3 to 3/4 of the thickness in the ridge being below the level ice. There were also areas where an ice floe would break (a big crack) and separate to form a spot with open water which would then freeze into very thin new ice. It is these areas without ice or very thin ice that we had to be most careful of as there was basically 1500m (4500ft) of icy cold water beneath that thin ice. So we had to be very careful not to fall through the thin ice sections.
Note from Mr. Harris:  A stress is a force (push or pull) acting on the ice, usually from the wind, or ocean currents.
Stress buoys.As for the stress gauges, these are steel cylinders with a hollow center. Across the hollow center there are three fine wires and a magnet which plucks the wires like a string. The frequency (or sound) of the wire lets us know how much pressure or pull the ice is experiences. This tells us important information about how the ice is pushing and pulling against itself as it moves about. The best analogue I can think of for stress is to consider the classic children's game called "Don't Break the Ice" or "Booby Trap" where you set pieces tightly together or with a rubber band pulling on one side. Then as you remove pieces, the stress builds up in different places so that different pieces feel different stresses. If you remove one too many pieces, the stress completely releases and things fall apart. In our case, we often see the reverse happen, where the booby trap game is now being compressed even more so that some of the pieces move above and below.
Courses in physics and especially engineering are super for learning about this type of behavior. We are learning how ice behaves as a material (from the field of material science). It breaks the way glass and many metals break but it can be handled at temperatures that humans can deal with as it gets soft near the melting point. That's one of the many reasons why people study ice, especially the polar sea ice. The Arctic is essentially a giant natural laboratory where we can watch and measure these events and that is why we use a stress gauge.
Hope this answers your question in a way that makes sense.
C:-)Dr. Cathleen GeigerResearch Associate ProfessorDepartment of GeographyCenter for Climatic ResearchUniversity of Delaware