Why does ice float on water?

What the evidence shows

Density and Buoyancy

Ice has a lower density than liquid water¹². There is a clear density contrast between glacial ice and liquid water³.

At least 1/9 of floating ice sits above the ocean surface³. This amount depends on the amount of pressurized air bubbles inside the glacial ice³.

Marine Environments

When sea water freezes, it creates ice with brine-filled channels¹. These channels provide a home for organisms like bacteria, algae, and copepods¹.

Floating ice creates a sheltered environment for plants and animals beneath it¹. Thin ice also lets light through to support photosynthesis¹.

Physical Properties

The density curve of ice is unusual and essential for life on earth². For temperatures below 4 °C, this curve creates a stable layering².

Ice can change into different forms under pressure². These polymorphs, such as ice II or ice III, have a higher density than liquid water².

What we can't say for sure

The exact height of an ice shelf above the sea depends on the density of the snow and firn sitting atop the glacier ice³.