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May 12, 2005

Of slime and sea ice: Microorganisms have physicists considering biology

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Bacteria, viruses, single-cell algae and other microorganisms waging a battle to keep themselves from freezing in sea ice appear to make ice malleable enough to trap ice breakers and could be affecting how sea ice changes and melts in places like the Arctic.

The importance of sea-ice microorganisms for polar marine food webs has long been known. In the Arctic, ice algae alone accounts for nearly 50 percent of the primary production, that is the production of new plant material during photosynthesis. But researchers are now considering their impact on the ice properties that they colonize, according to Christopher Krembs, an oceanographer with the UW’s Applied Physics Laboratory.

“Do you know how unusual it is for physicists studying how sea ice forms and melts to pay attention to the biology?” Krembs asks. “They’ve thought it irrelevant before this.”

That’s because it wasn’t until 1999 that Krembs serendipitously documented how microorganisms in sea ice were producing a special kind of “slime,” just as microorganisms in soils, rocks, sediments and oceans are known to do.

Among other things the slime — actually an extracellular polymer — can coat microorganisms and protect them from harsh conditions, provide a slick mat for them to move across, help them mass together or even change the surrounding environment to the benefit of the microorganisms. How this happens in sea ice has been the subject of two National Science Foundation projects led by Krembs.

Microorganisms are found on the bottom and throughout sea ice wherever there are nutrients, light and pockets or channels — some large but many microscopic — filled with brine, or salty water. The brine in sea ice can have such high concentrations of salt that it won’t freeze even at temperatures as low as -35 degrees C (-31 degrees F).

When it’s cold enough for even the brine to freeze, the microorganisms surround themselves with extracellular polymer. This is not a conscious choice, rather it’s what they do when under stress, Krembs says.

The microorganism and the extracellular polymer start changing the environment in a number of ways. For example, the extracellular polymer helps retain even more salt in the ice, increasing the fraction of unfrozen liquid brine. More salt also means the ice is more porous. That, along with the microorganism working to enlarging their brine channels, actually changes the mechanical strength of the ice from brittle to something much more malleable.

“When ice is filled with extracellular polymer you can knead it with your hands,” Krembs says.

The changes in ice triggered by the microorganism and extracellular polymer were suspected by one of Kremb’s colleagues as he watched an ice breaker near McMurdo station in the Antarctica get bogged down in the ice. Ice breakers move through ice-covered waters by propelling their hulls up and onto ice in front of them, cracking the ice under their weight. To work, the ice needs to be hard and brittle. Ice made malleable with extracellular polymer would be a whole different challenge.

Just how the biota may affect ice sheets is one of the current interests of Krembs, who is working on the question with Hajo Eicken from the University of Alaska Fairbanks.

“There is the possibility of an exceptionally interesting feedback between sea ice and associated biota, similar to those found in the weathering of rocks and the cohesiveness of soils and sediments,” he says.

Krembs left Tuesday for a NSF-supported field station operated by the Barrow Arctic Science Consortium in Alaska. On one of his trips earlier this year, the Applied Physics Laboratory paid the way for a two-student film crew from the Seattle Art Institute to go into the field with him. They and five of their fellow students are producing a 5-minute science film with video and animations created by the students.

Janet Olsonbaker, a multimedia program development manager at the Applied Physics Laboratory, wrote the script for the video and came up with the title, Life of Sea Ice, which refers both to the changes sea ice undergoes during the year and to the life living on, under and in the ice. The Applied Physics Laboratory will use the video in presentations at science meetings, when faculty visit schools and as a clip on a newly installed, interactive big-panel screen in its lobby.

The Seattle Art Institute connection started when Michael Steele, senior oceanographer at the Applied Physics Laboratory, was recruited as a guest lecturer on polar science and climate by Michael St. John, one the institute’s science teachers.

Since then Steele has had a science class from the institute visit the lab once a quarter, the next visit being later this month, and he started talks between the institute and Applied Physics Laboratory about internships or projects that could involve their students.

Life of Sea Ice is the first such project. Along with the five-minute film, which should be finished by June, other art institute students are making a 1-minute film about the making of Life of Sea Ice, which will be shown to students considering attending the institute so they have an idea of the kinds of projects that they might be able to work on.