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Ask Lyn: Beneath the Icy Surface

Wednesday, February 13, 2019

TWF Posted by: TWF

Dear Lyn,
The weather recently has really frozen the lake solid! What happens beneath that icy surface? Do you know what this means for the aquatic plants and animals this summer?


Dear FrozenFish,

What a complex and great question!

Let’s start with the why the lake freezes on the top. We’ve all made glasses of ice water, and the ice always floats, right? That’s because when water freezes, it has this amazing property that makes it less dense – allowing it to rest on top of the surface. (If you think about it, most solid objects are more dense than their liquid form – and if that were the case, the lake would freeze from the bottom up!)

Thanks to the floating ice, the water beneath it stays liquid, even on those crazy polar vortex days! This ice blanket also can pose a problem though…

The usual mingling of air, sunlight, and water is blocked – meaning that life beneath the ice slows down dramatically! We’re talking matrix speed.

The cold-blooded organisms often snuggle up in groups near the bottom. Some species, like frogs, burrow into soft sediments and go dormant, but most fish simply school in the deepest pools and take a “winter rest.” In this resting state, fishes’ hearts slow down, and lucky for them, their need food and oxygen decrease.

Why is that lucky? Plants also get to take a break from the usual photosynthesis business and go dormant until light can reach them again. This means that fish no longer can rely on the plants to produce oxygen, or provide much nutrients during the winter months.

Isn’t life under the lake’s surface amazing? This finely-tuned dance of chemistry and biology means that unless extraordinary circumstances continue past the usual winter months, we will see our usual plants and creatures springing back to life with the warmer weather!