Why does ice with many air bubbles look white?

Ice with many air bubbles appears white because the bubbles scatter all wavelengths of light equally.1

While pure ice is transparent, the presence of air bubbles makes it appear opaque. In dense ice, such as that found in icebergs or glaciers, the pressure of the ice formation process squeezes out these air bubbles. Without the bubbles to scatter all colors of light, the ice is able to absorb longer wavelengths (like red and yellow) while scattering and reflecting shorter blue wavelengths, which gives that ice its characteristic blue appearance. Conversely, when numerous bubbles are present, they interfere with this process by scattering the full spectrum of light, resulting in a white appearance.21