An ice primer

Sea ice is formed as seawater freezes. Because sea ice is less dense than seawater, it floats on top of the ocean. As sea ice forms, it rejects the majority of its salt to the ocean, making the ice even lighter. Because sea ice is formed from existing sea water, its melting does not raise sea level.

Fast ice is sea ice that grows from the coast into the sea, remaining attached to the coast or grounded to a shallow sea floor. It is important as a resting, hunting, and migration platform for species such as polar bears and walrus.

Pack ice refers to a large area of floating sea ice fragments that are packed together.

Ice caps and glaciers are land-based ice, with ice caps “capping" hills and mountains and glaciers usually referring to the ice filling the valleys, although the term glacier is often used to refer to ice caps as well.

An ice sheet is a collection of ice caps and glaciers, such as currently found on Greenland and on Antarctica. When ice caps, glaciers, and ice sheets melt, they cause sea level to rise by adding to the amount of water in the oceans.

An iceberg is a chunk of ice that calves off a glacier or ice sheet and floats at the ocean surface.

Source & © ACIA Impacts of a Warming Arctic: Arctic Climate Impact Assessment  (2004),
 Key Finding #1, p.24