Making sea ice 300 miles from the ocean
May 06, 2011
“We call it ‘Instant Ocean,’” he says, returning the lid to the jar. Mueller-Stoffels, a doctoral student in the Physics Department at the University of Alaska Fairbanks, uses the white contents of the jar - different types of salts found in seawater all over the world - to create homebrewed ocean. With that ocean, in a room held at minus 4 degrees Fahrenheit and 300 miles from the nearest tidewater, he grows sea ice of the type that floats on top of the world. He makes sea ice to help researchers like Hajo Eicken of the University of Alaska Fairbanks Geophysical Institute learn about the tiny pores that form in it, how salty brine moves through huge chunks of sea ice, and to see how those microscopic forces affect ice as a whole. “How well is sea ice able to retain water?” Eicken asked. “How much water pools at its surface in summertime (absorbing heat and encouraging ice melt)?” Northern sea ice is making headlines for covering less of the Arctic Ocean even in frigid darkness of midwinter. Some scientists think the Northwest Passage could be wide open in summertime within the next few decades. Some think it won’t take that long. Eicken looks at the microscopic properties of sea ice so he might learn something about the larger body of ice. Sea ice is different from fresh-water ice in that it forms at a colder temperature (about 28 degrees F) and is riddled with pores filled with brine. These crevices host a surprising variety of tiny life forms, from bacteria to algae. “Seals and polar bears all depend on microorganisms that live in ice,” Eicken said. Norwegian explorer Fridtjof Nansen wrote in 1897 that northern seal hunters called discolored ice “seal ice.” Where they found seals, there was ice darkened by billions of single celled algae living within it. Eicken and his colleagues Christopher Krembs of the Washington State Department of Ecology and Jody Deming of the University of Washington teamed on a recent paper in which they pondered whether the slime generated by tiny diatoms that live in sea ice alters their frozen environment to their advantage. The scientists wrote of a microscopic creature that lives in sea ice and produces “copious amounts of mucus.” “The slime they produce makes the ice much more porous,” Eicken said. “It helps them (resist freezing), while it reduces the strength of the ice.”
Sea ice made by Marc Mueller-Stoffels, who suspended chunks of fresh-water ice in salty brine at below-zero temperatures. He took this photo of a thin cross-section of ice using a polarizing filter. Individual shapes are ice crystals.
Making sea ice in Fairbanks is a matter of practicality for Eicken. He travels to Barrow often, and has in the past brought ice samples back with him, but it degrades quickly. To study it in detail he prefers to make his own “homogeneous, reproducible ice.” Mueller-Stoffels creates sea ice for Eicken one batch at a time. The salty liquid mixture he places in the cooler freezes in a plastic container, often leaving unfrozen slush at the bottom. When the ice and brine mixture hardens, he slices it with a band saw and then locks the rectangles of ice on a lathe and turns them. He shaves the ice until it is an opaque cylinder that fits in his palm. He later x-rays that cylinder of ice, which enables researchers to see in three dimensions the relationship between the ice crystals and the pores filled with brine. “We use it to drive models,” Eicken said. “How can we describe this type of behavior in simpler terms?” Mueller-Stoffels, from Germany, enjoys the challenges of making ice in a place (Fairbanks, Alaska) that gets much more extreme outside than it is in his indoor walk-in freezers. “During cold spells I walk into the freezer and think it’s broken,” he said.
This column is provided as a public service by the Geophysical Institute,
E-mail your news &
photos to editor@sitnews.us
|
||
