Whether it's a few-gram ice cube in fruit juice or a multi-ton iceberg in the North Atlantic Ocean, the physical reality is the same: ice floats. This is an indisputable fact.
Floating ice is “It's such a fundamental truth about the world that it's hard to really imagine what the world would be like [sans elle]”“, notes Brent Minshew, associate professor of geophysics at the Massachusetts Institute of Technology, in Live Science. But how can we explain this phenomenon?
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Ice is denser than liquid water
To understand why ice floats, we have to look at the molecular structure of water. The latter actually has a peculiarity that distinguishes it from most materials. While the latter is heavier in the solid state, this is not the case for water, which has a lower density when frozen. “Water is a very unusual substance.”L confirms Live Science Claire Parkinson, a former climate scientist at NASA's Goddard Space Flight Center in Maryland.
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A water molecule (H2O) consists of two hydrogen atoms and one oxygen atom. These atoms share pairs of electrons. A so-called hydrogen bond occurs: the positive charge of a hydrogen atom is attracted to the negatively charged oxygen atom of another water molecule. “When water freezes, these hydrogen bonds form a crystal lattice.”“, explains Brent Minshew.
“Most of the ice on Earth is made up of repeating hexagonal crystals. There is a lot of empty space in this lattice structure that fills with air, causing the ice to become less dense.”he adds.
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When water is a liquid, the molecules that make it up are constantly moving and shifting relative to each other. The connections between them are soft and puffy. But when water is in a solid state, the molecules are very far apart from each other, forming a large crystal lattice, and the bonds are straight and tense: therefore, ice occupies more space than liquid water. So a 1 liter bottle of ice water weighs less than 1 kilo and will therefore float on the surface. Conversely, a one-liter bottle of liquid water will sink to the bottom.
Icebergs, floating giants beneficial to aquatic life
This may seem unbelievable, but we now understand why icebergs 50 meters thick float on the surface of the ocean. As Claire Parkinson explains, fortunately! “This is a good thing because floating ice allows life to flourish beneath the frozen surfaces of lakes and oceans. If the ice sinks, it will pose a problem for marine and aquatic life that currently lives in these submarine habitats.”The world notices.
These icebergs also participate in ocean water circulation by creating extremely dense, salt-laden water that sinks to the ocean floor and pushes deeper water toward the surface.
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But floating ice also represents a danger, this time linked to global warming. A 2023 study published in the journal nature It is expected that the floating ice shelves that make up the West Antarctic Ice Sheet will shrink rapidly over the next century as rising ocean temperatures melt the shelves.
Their melting will not directly cause sea levels to rise, precisely because they float. But as they melt, there is a risk that more of the ice held by these shelves will be released into the oceans.
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