Ice is Magic

published Feb 5, 2020 in the York Weekly, Portsmouth Herald and Foster’s Daily and online at seacoastonline.com

I spent almost the entire first semester last year having my freshmen STEM class run experiments about ice. Every morning, when I walk my dog, we follow a path along the river and observe the ice, marvel at the huge slabs of ice that are carried downstream and stacked like pancakes in some places, crunch our way over the paper-thin ice that coated the hummocks of the floodplain after the last brief thaw, watch dangling orbs of ice form in the waterfall that spills down to feed the river. I, like so many others, am obsessed with ice.

If you think about it, ice formation on a pond or lake is fairly straightforward. As the water gets colder, it gets denser and starts to sink. Liquid water reaches its maximum density at 4 °C (39.2 °F), after that it continues to get colder and freeze solid, but as it freezes, it becomes less dense and floats to the surface and we end up with ice-covered lakes.

Ice slabs pile up in Little River

At first, the ice is paper-thin, fragile sheets that crumble in your hand. As winter’s cold progresses, the ice gets thicker and thicker as more ice is added from the bottom. As long as the pond or lake is deep enough, there should always be at least some liquid water underneath the ice. This is very helpful to the animals that live in the pond or lake. They can survive in the liquid water near the bottom until the spring thaw.

Now, think about a river or stream in which the water is constantly moving. All of that turbulence makes it difficult for a nice sheet of ice to form. On cold winter nights, the surface water of a river cools, crystals of ice form and start to grow. The constant water movement keeps the crystals from growing together into a solid sheet, instead you get a slushy mixture of water and ice called frazil ice. You can see this floating on the top of a river in early winter, or instead of floating on top, because the crystals are so small, they can easily be carried by the turbulence down to the bottom of the river.

Ice slab close-up with river behind it

As temperatures continue to drop, the frazil ice can start to join together at the surface and form round plates of ice with upturned edges (from the plates bumping together). This is called pancake ice. Or, what was more common on my river, ice will start to form along the edges of the river. Ice forms more easily along the edges because there is typically less water movement and the temperature of the shallow water on the edge cools faster. This is called border or shore ice. Border ice will generally enlarge toward the middle of the river until the ice from both sides meet.

Border ice forms along a small stream

Another interesting way a river can freeze is when the frazil ice that is transported to the bottom of the river attaches to the streambed and builds from the bottom up. This is called anchor ice. Anchor ice can grow very rapidly and block the flow of a river or stream causing local flooding. If there is particularly low flow of water along the bottom, an enormous amount of anchor ice can build up. This can be extremely harmful to aquatic life because the anchor ice can physically lift up parts of the streambed and move it downstream, movement akin to the action of a bulldozer, killing small fish and aquatic invertebrates (like dragonfly or caddisfly larvae) that live in the streambed, or freezing fish eggs that were waiting for spring to hatch.

I thought I first fell in love with ice in some dramatic location, perhaps when I crossed Lake Champlain on the ferry one cold winter’s night and watched the prow cut through the ice and listened to it grind against the hull of the boat, or when I was travelling as a National Geographic Grosvenor Teacher Fellow in the Arctic Ocean and witnessed firsthand the ethereal beauty of icebergs and the vast expanses of pack ice in the polar sea. But watching the beautiful, ever-mutable ice along my little river this winter has made me realize that I’ve loved ice since I was a kid watching icicles dangle from the gutters of my house, that no matter where you find it, ice is magic.

In winter’s cold, the subnivean zone is abuzz

Published January 21 2020 The York Weekly, Portsmouth Herald and Foster’s Daily and at seacoastonline.com Titled ‘Nature News’

The subnivean zone lies between the snow and the earth.

This winter has been troublesome; a few weeks ago it was so cold my pipes froze, then it we climbed to unseasonably warm temperatures, then some more snow, and now, very cold again-my pipes continue to freeze. One thing that makes me happy is that we have a nice layer of snow on the ground, insulation that is is vital to the survival of many of the plants and small mammals, even microscopic life forms, that are essential parts of our Northern ecosystem. So, for many, the recent snow was welcome relief from the cold.

While the surface seems empty, underneath, at the interface between ground and snow, a veritable city is rising. Old leaves and branches hold the snow up, creating an open space. The ground also radiates heat, warming the overlying snow, which instead of melting sublimates (when a solid turns into a gas without first becoming a liquid) directly into water vapor. Both of these processes leave a space between the snow and the ground, called the subnivean zone.

The word “subnivean” comes from the Latin for under (sub) the snow (nivean) and is a scientific term referring to the open passageways that form under deep snow.

Six or more inches of snow are all that are needed to trap the earth’s heat and allow a subnivean zone to form. This zone remains humid because of the transformation of snow into moist water vapor and is capped by a layer of ice that acts as an insulating roof. The temperature of the subnivean zone is generally a constant 32 degrees, protecting species that would otherwise freeze.

The most common inhabitants of the subnivean are mice and voles — they make tunnels under the snow connecting sleeping areas and sources of food. Red squirrels also burrow into the subnivean to stash food. Entrance holes to these networks allow carbon dioxide to escape. Carbon dioxide is released when these animals breathe and by the ground itself. Without the entrance holes to serve as ventilation shafts, carbon dioxide could build up to lethal levels.

While the subnivean zone provides protection for mice and voles, it is also the hunting ground for the short-tailed weasel (or ermine), a weasel that, except for its black-tipped tail, turns snowy white in the winter. This small weasel, just the right size to live and hunt in the tunnels under the snow, is a major predator upon small rodents.

All you need is about 6 inches of snow to allow the subnivean space to form

Recent research has unearthed a whole new category of inhabitants of the subnivean zone — microbes that are proving to be important players in the cycling of both nitrogen and carbon dioxide between the earth and the atmosphere. A deep snowpack with an active subnivean zone appears to encourage a healthy microbial population that, through respiration, releases significant amounts of carbon dioxide into the atmosphere. Studies suggest that as much as half of the carbon taken up by plants in the summer is released back into the atmosphere by microbes in winter (Paul Brooks, University of Colorado Boulder). At the same time these microbes, by processing and storing nitrogen, fertilize the soil as the snow melts.

Without a healthy snowpack, without these snowpack microbes, plants don’t do as well come spring. While these microbes may be releasing a lot of carbon into the atmosphere during the winter, they are also necessary for healthy plant growth — plants that will absorb carbon dioxide throughout the growing season.

For all these reasons, it seems to me, a nice deep snow, serving as an insulating blanket on the earth, is a welcome part of our northern winter.

Red Crossbills in New England

published Dec 17 2019 The Portsmouth Herald/seacoastmedia.com

I have been watching the “winter” birds return to my feeder – juncos and titmice, downy and hairy woodpeckers, cardinals and nuthatches. A birding friend who lives in Colorado just posted some gorgeous photos of red crossbills in his hometown of Estes Park. He said he is seeing them everywhere. I have never seen a crossbill (a type of large finch) even though we have both red and white-winged crossbills in New England, particularly in the winter. The North American range of the red crossbills that my friend Scott Rashid, founder of the Colorado Avian Research and Rehabilitation Institute, photographed extends down into the mountainous spruce and pine forests of Central America, while the white-winged crossbill range is mostly in the boreal coniferous forests of the north.

Both of these crossbills could, I think, be mistaken for a house or purple finch by a birder of my caliber (poor). I wonder whether I have seen crossbills in my backyard, but assumed they were house finches? Crossbills are larger than house and purple finches and both the white-winged and the red crossbill are rosy red all over with dark wings whereas the house and purple finches are reddish mostly in front. I’m describing male coloration – the females of all these species are drab, with the finch females being brownish and the crossbill females being yellowish-green.

Crossbills have a really wonderful adaptation to their lives in coniferous forests. Their bills cross at the tip so that when their bill is closed the tip of the bottom bill protrudes up and the tip of the top bill protrudes down forcing the upper and lower parts to cross each other. According to the Cornell Laboratory of Ornithology, crossbills employ a special technique using these unique bills to get to their favorite food, pine seeds. “A bird’s biting muscles are stronger than the muscles used to open the bill, so the Red Crossbill places the tips of its slightly open bill under a cone scale and bites down. The crossed tips of the bill push the scale up, exposing the seed inside.” They then extract the seed using their tongue and bill together.

One fascinating fact about red crossbills that Scott shared with me was the wide variety in overall size and particularly in bill size among what is now considered the one species of red crossbill (Loxia curvirostra). For example, there are types of red crossbills that are smaller in size with smaller bills who specialize in the smaller pine cones of hemlock trees while larger billed types will specialize in larger pine cones. There are currently 11 different types of red crossbill recognized in North America.

Another cool fact about both red and white-winged crossbills is that they are opportunistic breeders. Because their diet is largely composed of pine seeds (white-winged crossbills can eat up to 3,000 conifer seeds in one day!), because they feed pine seeds to their young, and because pine trees produce cones at different times of the year, these birds can breed whenever the seed crop is largest. This might mean nesting in the depths of winter – something I wouldn’t expect to see, a nest with young or some fledglings hanging out on a snowy afternoon.

The best time to find crossbills around is in the winter as they wander about in search of food. According to the Cornell Lab, “Crossbills are nomadic, especially in winter, and in some years irrupt far south of their normal range. At these times, they may show up in evergreen forests, planted evergreens, or at bird feeders.” Sometimes cone crops will fail in their breeding ground and migrants will show up further south in search of food. Making sure to include a variety of native conifers in your backyard can help attract them. Cemeteries and parks with ornamental spruce and pine plantings are also a good place to look as they often attract crossbills in winter.

Everyone I know who is a “real” birder has seen crossbills in New England in winter, so my personal challenge is to try to join the ranks. To that end I’ll be paying a little more attention to anything that looks like a house finch and to any reddish-pinkish birds hanging out in my conifers and feeding from the pine cones dangling from the upper branches.

Susan Pike, a researcher and an environmental sciences and biology teacher at St. Thomas Aquinas High School, welcomes your ideas for future column topics. She may be reached at spike3116@gmail.com. Read more of her Nature News columns online.