Sea ice refers to the accumulation of frozen seawater that forms on top of oceans, particularly in polar regions. It is different from land-based glaciers and ice caps which form over land areas. Sea ice can vary greatly in thickness, ranging from thin layers of frazil ice (which is a mixture of small ice crystals and snowflakes) to multiyear ice that persists for several years or even decades.
Sea ice plays an important role in regulating the Earth's climate by reflecting sunlight back into space, which helps to cool the planet. It also provides habitat for marine mammals such as polar bears and seals, and serves as a platform for human activities like fishing and oil drilling. However, sea ice is highly sensitive to changes in temperature, and its extent has been rapidly declining due to global warming. This loss of sea ice can have significant impacts on marine ecosystems and the communities that depend upon them.