Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [7]
There is something quite remarkable, simple, and yet profoundly important that happens when water turns to ice in a pond. Compare this with what transpires when water turns to ice in a cloud. In a cloud, the ice crystals fall because water and ice are heavier than air and the gas phase of water. However, water becomes lighter when it transforms from a liquid to a solid state. If this were otherwise, then ice crystals would sink as soon as they formed on the surface of a pond. Heat near the bottom of the water would at first continually melt the ice crystals coming down, but at some point temperatures near the bottom would reach 0°C and lower. The water would then freeze from the bottom up, rather than from the top down. The ecological consequence of this phenomenon would be that there would be no bodies of water in the north. Sunshine in the summer would melt only the upper layers of ice, and any aspiring body of water would soon become a huge permafrosted ice lens.
Another ecologically important aspect of the behavior of water is that its density changes with changing temperature. Cold water is denser than hot water, and so cold water sinks as hot rises. As is also true for air. But, in water, the change is not so uniform. Water becomes densest at 4°C. As a result, when lakes warm up in the springtime from 0° to 4°C, as the ice melts, the surface water sinks. This denser water displaces the colder bottom water and its nutrients, which then rise toward the surface and feed the life above.
Geologically, the earth has experienced regularly recurring ice ages that are dependent on an astronomical cycle of the earth’s tilt (Imbrie and Imbrie 1979). This, the Milankovich cycle (named for its discoverer, Milutin Milankovich), is currently in a cooling period that began seven thousand years ago. But at the present time we are experiencing global warming instead, because the cooling effect of the astronomical cycle is being overridden by a human-induced climate change. The burning of fossil fuels produces carbon dioxide gas that is accumulating in the atmosphere at a greater rate than it is being absorbed by forest trees and other plants. The carbon dioxide acts as a thermal blanket, trapping solar heat. Unlike the astronomical cycle, which is gradual and permits evolutionary adaptations, this new phenomenon in the history of planet earth is sudden. It will affect kinglets, and us.
02
SNOW AND THE SUBNIVIAN SPACE
Sometime early in October the brilliant foliage comes to rest on the forest floor. And then one morning those leaves are encrusted with the white ice crystals we call hoar frost. A few weeks later the first snowflakes, the conglomerates of innumerable snow crystals formed in the air, may come spiraling down out of a darkening sky. Kids of all ages focus on the largest ones and make a game of maneuvering under them to try to catch them on their tongues.
Wilson Alwyn Bentley, or the “Snowflake Man” as he came to be known, also caught snow crystals on microscope slides. He lived on his family’s homestead in the village of Jericho, Vermont, along with his brother Charles, their parents, their grandparents, and later Charles’s wife and their children.
Life on the farm revolved around the chores and seasons, and on February 9, 1880, on his fifteenth birthday, Wilson received an old microscope as a gift from his mother. It changed his life. “I found that snowflakes were miracles of beauty,” he would say later. “Every crystal was a masterpiece of design, and no one design was ever repeated.”
As a result of Bentley’s writing and photography on the subject, every schoolchild is now taught that no two snowflakes are alike, although he pointed out that “it is not difficult to find two or more crystals that are nearly, if not the same, in outline.” Snow crystals were to him a metaphor for earth’s beauty. They were a “road