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Marine Life Encyclopedia

Marine Science and Ecosystems

Ice Edge


Arctic and Antarctic polar waters

Physical Ocean Characteristics

Keystone Species

Ecosystem Services

Sea ice at both the North and South Poles forms a variety of dynamic ecosystems that change with the season. Several iconic species rely on sea ice formation and movement for some or all of their life history stages. As the poles continue to warm, in the face of ongoing climate change, sea ice ecosystems are at risk of being lost or permanently altered.

In order to understand sea ice ecosystems, it is important to understand the ice itself. Not all sea ice is the same. Scientists classify this ice based on its ability to drift and its age. Ice that is attached to the shore or to the seafloor is called ‘fast ice’ because it is ‘fastened.’ Ice that is adrift is simply called ‘drift ice’ or ‘pack ice’ because of its tendency to ‘pack’ together along currents. The Arctic is an open ocean surrounded by land, so fast ice occurs around the boundaries, while drift ice occurs in the middle. In Antarctica, land is surrounded by open ocean, so fast ice occurs around the central landmass, while drift ice forms outer rings. New ice is ice that forms in the winter and melts in the summer. Old ice is ice that survives the summer and grows for at least two years. Generally speaking, old ice is thicker and stronger than new ice.

Sea ice serves as the foundation of multiple unique, but overlapping, marine communities. 1) The ice surface is important habitat for seabirds and marine mammals that use it for mating, caring for their young, and resting between trips feeding underwater. Some examples include polar bears, ringed seals and other seals, walruses, and a variety of penguins. As sea ice expands each winter, some of these species are able to expand their feeding grounds, by following the ice edge into deeper water, farther from land. 2) The underneath edge of sea ice supports a very productive planktonic community that thrives on nutrients released by melting ice. Krill and other important prey species benefit from this microscopic community and in turn support productive open ocean communities that include species as big and iconic as the blue whale and also important fisheries species. 3) Finally, the benthic community on the seafloor under ice that forms in shallow water is affected by ice formation and melting. Thick ice can fasten to or scrape along the seafloor, often completely shearing off all life attached to or utilizing the seafloor. Whenever this removal occurs, new communities of potentially different species are able to begin to form.  In this manner, the sea ice drives an ongoing cycle between young and mature marine communities on the seafloor.

Unfortunately, sea ice is currently changing in new ways, as a result of ongoing climate change. Growing human emissions of greenhouse gases are warming the planet. Regional wind and oceanographic patterns cause the poles to warm at a must faster rate than the planet as a whole, so sea-ice ecosystems are experiencing faster, more significant changes than other marine systems. With these changes come threats to the communities and species that rely on sea ice for their continued survival. Scientists fear that all old ice from the Arctic could be gone in the next two decades, and old ice is being lost in Antarctica at an alarming rate. New ice will continue to form each winter, but the lack of old ice in the summer will alter these ecosystems. Unless current sea-ice trends are reversed, amazing polar species may be lost.

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