Nature Notes

The Iceman Cometh!

By Boak Wiesner

The reports of the end of the Universe have been grossly exaggerated, to cop a quip from Twain. Are calendars really accurate, anyway, when we stop to consider how short our time on Earth is but how long bodies in the cosmos have been moving in their spheres? We did experience the Winter Solstice Friday morning but how ephemeral, even, events like the solstice are, really, as the exact time during our yearly orbit about the Sun it occurs is slowly, at least to us, changing, as the precession of the axis of rotation of the Earth moves where the North Pole is pointing from nearly directly at Polaris, as it is now, to pointing ever more closer to the star Vega. Yeah, it’ll take 13,000 years to get there, but still.

After the recent snow it was time to head outside to measure the temperature at different levels of the snow pack. Once again, I was impressed at the insulating ability of even a thin cover of the white stuff. When it was well below zero, Celsius, that is, it was a smidgen above freezing under the snow at the surface of the ground.

DSC_0135All the heat the earth absorbs during the summer and fall is still down there; it just needs a nice “blankie” of snow to allow it to spread up to the top again. The critters that made these tracks can enjoy a fairly open area under the snow, the depth hoar, where they are protected from the sharp eyes, though not the ears, of aerial and earthbound predators as well as the bitter cold of the atmosphere above.

Ice, too, amazingly shows important insulating properties. Because of the strong polar nature of the water molecule (which means one molecule sticks to another in a very definite hexagonal manner)  ice is significantly less dense than its own liquid self. Pretty cool! Thus the water under the ice can never really get colder than freezing, and, because a lake has to freeze from the top down, most of the vertical column of water in a lake stays watery all winter long allowing fish and other animals to move about.

DSC_0175Lay down on some nice clear black ice some bright day and you might see a turtle or a frog moving about slowly down there! Because as poikilotherms, their physiology has slowed down so much they are able to absorb all the oxygen they need from the surrounding water. Come spring they will emerge a little skinnier but none the worse for wear.

Boak Wiesner is a Minnesota Naturalist volunteer.


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