Chipper Adventures: What Happens When Water Freezes Over?

With Winter in full affect, lakes and waterways have frozen over. Chipper has always wondered, what happens to all the flora and fauna below the surface? To answer this question, we first have to take a look at the chemical properties of water.

In general, most substances become more and more compact as they are cooled. However, the nature of water is such that, as it freezes, its molecules join into rings, each of which takes up more space than the same number of liquid molecules. This means that ice (frozen water) is less dense than liquid water. For this reason, ice is lighter than water and will, in fact, float on water (which is why icebergs float).

Now, think of what happens to a pond or lake as the temperature cools and the water begins to freeze. As ice crystals form, they float to the surface of the water. Eventually, the entire surface freezes over, covering the bulk of the water underneath, which is still liquid. Once the ice forms, it acts as insulation, helping to retain heat in the liquid below.


Thus, unless the temperature is extremely low for a very long period of time, the water below the ice does not freeze, although the ice may grow thicker. In a normal winter, the cold does not last long enough to freeze all the water, so the fish are able to live just fine until the coming of spring warms the surface and melts the covering of ice. Also, oxygen is trapped beneath the layer of ice, allowing fish and other aquatic animals to live comfortably in the frozen lakes and ponds.

Different animals have developed various patterns and characteristics to survive the cold winter months. Male pink salmon and some sockeye salmon develop pronounced humps just before they spawn. The humps make it less likely the salmon will spawn in the shallow water at margins of the stream bed, which tend to dry out during low water flows or freeze in winter.

Certain species of cod, flatfish and polar fish have a reduced metabolic rate and produce antifreeze molecules called glycoprotein to reduce the freezing point of their body fluids. One could look at it as the fishy version of bears hibernating, a survival tactic that has seen these finned friends outlive many other creatures on Earth.

When water bodies freeze over, the waterfowl, like ducks and geese, migrate south to enjoy the warmer weather and hunt for fish. Animals like seals, penguins, walruses and a wide variety of sea birds are all fish eaters and survive in the extreme cold. They live in the Arctic and Antarctic Circle, amidst the icecaps. The land is completely frozen. Yet these animals manage to live in this region because they are warm-blooded and keep warm through their fur like all mammals. They also have a large layer of fat which helps keep them warm.

As for flora, some hardy plants in large bodies of water can survive a surface freeze. If a heavy amount of snow accumulates on the ice surface of lakes, the amount of light penetrating through the ice will be reduced. This will result in less light reaching aquatic plants below the ice which is needed to carry out photosynthesis thus, causing the plants to die and be broken down by bacteria. These bacteria will then use up the oxygen and cause a drastic drop in dissolved oxygen in the water. When this winter oxygen depletion occurs, marine life such as fish that depends on oxygen will die. As fish and other marine life die, their bodies decompose and use up even more oxygen, and the depletion of oxygen gets even worse. This is called “Winterkill” and can be very damaging to fragile ecosystems.

Anyway you look at it, the winter brings the harsh cold but there’s plenty of fun to be had as well: ice skating, skiing, sleighing and more! What’s your favorite thing about winter? Share with Chipper!