Multiyear Ice

Multiyear ice has distinct properties that distinguish it from first-year ice, based on processes that occur during the summer melt. Multiyear ice contains much less brine and more air pockets than first-year ice. Less brine means "stiffer" ice that is more difficult for icebreakers to navigate and clear.

Hummocks of multiyear ice that are several years old are fresh enough that someone could drink their melted water. In fact, multiyear ice often supplies the fresh water needed for polar expeditions.

First-year and multiyear ice have different electromagnetic properties that satellite sensors can detect, allowing scientists to distinguish the two. For more information, see Remote Sensing in the Studying section.

Multiyear ice is more common in the Arctic than in the Antarctic. This is because ocean currents and atmospheric circulation move sea ice around Antarctica, causing most of the ice to melt in the summer as it moves into warmer waters, or as the upper ocean heats up due to absorption of solar heat by open water areas. Most of the multiyear ice that does occur in the Antarctic persists because of a circulating current in the Weddell Sea, on the eastern side of the Antarctic Peninsula.

In contrast to Antarctica, the Arctic Ocean is relatively landlocked. Historically, this land-ocean configuration allowed extensive multiyear ice to form. In recent years, multiyear ice has declined significantly in the Arctic. Sea ice typically travels across the Arctic with ocean currents, and sea ice exits the Arctic Ocean through the Fram Strait east of Greenland. The Beaufort Gyre, a circular current north of Alaska, used to act as a nursery for young sea ice where it could persist and thicken over time. Since the start of the 21st century, most ice has melted in the southern arm of the gyre, allowing much less multiyear ice to form. The Fram Strait, however, continues to serve as a sea ice exit ramp out of the ocean basin.

Arctic ice age comparison
In March 1985, sea ice that had survived at least four summers comprised 33 percent of the Arctic ice pack at the winter maximum. In March 2019, such long-lasting sea ice comprised just over 1 percent.
—Credit: NOAA Climate.gov, based on the Arctic Report Card: Update for 2019

Last updated: 3 April 2020