Polar bears face deep freeze …on their feet

              When I was teaching American history, I used to describe the depression by spinning a yarn about a fictional farmer who’d already been through loads. Fluctuating prices meant never knowing what to plant. Although cars gave you enough mobility to have a social life, you were still limited to people you could reach. Then you get an eleven-year drought. Choking dust clouds kill your animals and the only two neighbors you liked. But you look out the window and you see, hanging on your clothesline, which you’ve propped up on two sticks of wood, your last pair of socks. Your mom always said you can get through anything if you have a good pair of wool socks. Then you see a cloud on the horizon. It doesn’t look like rain or dust, and it’s making a funny noise. It gets closer and you see it’s not a cloud. It’s grasshoppers. They descend on your house and eat your surviving crops. And your clothesline. And your socks.

              There were parts of the Dust Bowl that we inflicted on ourselves. Western plowing techniques ripped up the long-rooted grasses that had held the topsoil in place and prevented the dust clouds that gave the disaster its name.

              Polar bears have been going through their own human-induced Dust Bowl in the form of melting polar ice. Without ice sheets to walk on, the polar bears cannot as large a portion of the year at sea hunting seals as they usually would. Some become stranded on dry land year-round, necessitating changes in behavior. But up until now, polar bears could, like my fictional farmer, at least count on reasonably comfortable feet.

              No more. In findings published this week in Ecology, scientists from the University of Washington report that climate change has reaped yet another indignity on the world’s largest land predator: chunks of ice, sometimes as large as a foot (31 cm) in diameter, stick to their feet, causing injury, scarring, and the loss of protective hair.

              Polar bears’ feet have irregular surfaces for better traction on the ice, far more so than other bears’ feet or the feline “toe beans” so beloved by the Internet. Unfortunately, what helps the polar bear stick to the ice can also make the ice stick to the polar bear.

              “The two most affected bears couldn’t run — they couldn’t even walk very easily,” said lead author, Dr. Kristin Laidre. When immobilizing them for research, we very carefully removed the ice balls. The chunks of ice weren’t just caught up in the hair. They were sealed to the skin, and when you palpated the feet it was apparent that the bears were in pain.”

              The study covered two populations, one in Greenland, and one between Greenland and Canada, all north of Baffin Bay. The research team reviewed the results of earlier formal surveys and consulted with local indigenous hunters, and all sources agreed that this phenomenon is new.

              Laidre and her co-author, wildlife veterinarian Stephen Atkinson, came up with three possible explanations for this phenomenon, all related to climate change. There could be an greater number of rain-on-snow events, which have already been reported to affect seals and ungulates. The change in global temperature could be causing more frequent freeze-thaw cycles (think the parts of spring and fall with frosty mornings and hot afternoons), in which wet snow or water sticks to the polar bear and then freezes solid. It is also possible that warmer days cause the surface snow to melt and then refreeze at night, creating a crust that collapses under the bears’ weight. Third, the bears in this study all lived near coastal glaciers, which, unlike sea ice, are made of fresh water. This could allow seawater to seep upward, soaking the bears’ feet.

Read the study in Ecology. <https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecy.4435>

Laidre K. and Atkinson S. Icing-related injuries in polar bears (Ursus maritimus) at high latitudes. Ecology, (2024). DOI: 10.1002/ecy.4435