glacial ice

The ice that is seen floating on the ocean’s surface comes from one of two sources. Glacial ice is formed from the accumulation and compression of snow into glaciers, that then break apart and release ice to the ocean. Because glaciers can be several kilometers thick the icebergs that break off of them can be very large; so the tall icebergs at sea always come from glacial ice sheets. Sea ice refers to the ice formed from the freezing of sea water, and rarely exceeds a thickness of several meters (Figure 14.1.1). Sea ice covers about 7% of the ocean at any time, and makes up about 66% of the Earth’s permanent ice cover by area, but only 0.1% of the ice in terms of volume. This is because sea ice is a vast but thin sheet of cover compared to the glacial ice caps that are more localized but may be several kilometers thick.

14.1 Types of Ice 2025