The Dirty Doings of Sea Ice
The last time I saw Willy Weeks, he was at the airport heading to a batch of meetings and an eventual vacation on the Turkish coast. This itinerary indicates that Weeks is remarkably level-headed for a glaciologist, because ice experts often seem to become ice addicts. They can go for years catching mere glimpses of the snow-free season we ordinary folks call "summer," spending June on Greenland's ice cap and December on Antarctica's ice shelves. Professor of Geophysics Weeks' willingness to spend time enjoying warmer places speaks well for his mental health.
As former chief scientist for the Alaska Synthetic Aperture Radar Facility at the Geophysical Institute, Weeks studies ice mostly at a distance, but he still gets into the chilly stuff, now and then, as indicated by the most recent issue of the journal Arctic Research of the United States. Among a collection of articles devoted to arctic contamination, Weeks provided "Possible Roles of Sea Ice in the Transport of Hazardous Material."
As soon as I read the title, my mental video played scenes of steel drums with threatening markings--the radioactive trefoil, the skull and crossbones, the frowning disk-like face of Mr. Yuk--being rolled onto voyaging ice floes. The article admitted my scenario, since the pack ice does swirl slowly around the Arctic, and the surface of sea ice has been the handy repository for all kinds of human-dumped wastes since before any of those symbols were used to signal danger. But Weeks wrote at greater length about other, more subtle possibilities.
One concern is that ice could sop up liquid nuclear wastes or other dissolved toxins from sea water. This worry gets short shrift in the article, because sea ice is almost self-purifying. When it first freezes, an ice floe is only about half as salty as the sea water in which it forms. Over the course of one winter, the ice will lose half to two-thirds of its initial salt burden. (Old-timers appreciate this feature of the Arctic, and melt the oldest sea ice they can find for drinking water.)
Solids are a different matter--even tiny specks of solids. Frazil ice, the ice crystals that form within the water rather than merely at its surface, can trap sediment particles. Just as a pearl grows around a grain of sand trapped in an oyster, frazil crystals form around particles in extremely cold, turbulent water. As they gather together, the disk-like frazil crystals behave like sticky gum, grabbing onto particles on the bottom if they encounter it, or scavenging other bits floating in the water. By the time the frazil crystals form a layer of slushy grease floating at the surface, they behave like a sieve, straining out more debris from the water. As the ice solidifies and thickens, the trapped solids get built right into its structure.
This suspension freezing process requires particular conditions--very cold temperatures and well-stirred water--that are not found everywhere in the Arctic. Most of the Arctic Ocean is sealed under an insulating windshield of ice floes during the deepest chill of winter. The sea water can't be stirred up by winds nor cooled down enough by the frigid atmosphere for frazils to form unless the ice has a good-sized opening--a polynya.
Weeks' article offers a not-too-likely worst-case scenario in which deep ice keels could gouge up the sea floor, rupturing drums of contaminants buried in the bottom and spreading their contents. If a polynya formed at the right spot, the suspension freezing processes could trap those contaminants, carrying them halfway around the top of the world before melting and releasing them.
That's the bad news. The good news is that the most worrisome sources of contaminants nowadays are in the western Russian Arctic; the pack ice drift will take material trapped there toward the North Atlantic instead of Alaska.
