Floe Edge

The floe edge is a constantly moving and dynamic line that marks the end of fixed fast ice (ice that is anchored to the shore) and the start of the Arctic Ocean. The word floe probably comes from Norwegian, where flo means a "flat layer." In English, a floe is defined as floating ice formed in a large sheet on the surface of a body of water. In the fall as the ocean freezes, the floe edge moves farther and farther out from land and may eventually completely disappear once the body of water is frozen completely solid. In the spring, as the ice starts to break up, the floe edge recedes and gradually comes closer to land until it eventually disappears completely. As the weather warms, a combination of currents and meltwater runoff form cracks in the ice known as leads. These cracks may be many kilometers behind the floe edge, but once they connect on both sides with free water enormous pieces of ice will float out and away. For this reason the floe edge very rarely recedes gradually, but rather in large pieces.

Animals tend to be abundant in open water near the ice edge, which is generally the most active biological area in the Arctic. As spring moves into summer, the Arctic Circle is immersed in 24 h of sunlight. The bottom of the pack ice becomes covered with single-celled algae. These algae are eaten by a number of small

Glacier Bay Alaska Ice Flow With Seals
Seal on an ice floe, Glacier Bay National Park and Preserve, Alaska. Copyright W.E. Garrett/National Geographic Image Collection

crustaceans, which in turn are consumed by a wide variety of invertebrates, fish, birds, and mammals. These birds and mammals seek access to the abundant food supply under the ice. Since birds and mammals must breathe, they cannot feed under fast ice and are thus often found feeding and resting in open water near the floe edge. Seals and walrus may also rest and warm up on the ice as it provides an easy escape into the water from polar bears that frequently patrol the edge.

Bowhead, narwhal, and beluga whales also gather at the floe edge, waiting for the ice to break up and open up migration routes to their feeding grounds. The Arctic whales can swim underneath the ice and find small holes that they can breathe through, as none have dorsal fins that would prevent them from aligning their blowholes flush with the ice. They cannot swim too far away from the edge, however, as they will suffocate if they cannot find a breathing hole. The whales use the ice as a sanctuary against orcas (killer whales), who will not pursue them under the floe edge. Orcas cannot breathe under the ice because their large dorsal fin makes it impossible for them to place their blowhole against the ice.

After an Arctic winter, ice can be many feet thick and is strong enough to safely support people, animals, and even snowmobiles right up to the edge. Inuit who camp on the floe edge must be careful that what may be fixed fast ice when they arrive does not break away some kilometers in and drift away. Hunting and tourist camps are frequently set up close to the floe edge because of the wildlife that moves along the edge. Attention must therefore be paid to ensure that the floe edge does not break and become the edge of a floating piece of ice, thereby leaving a new floe edge many kilometers back. People normally travel to the floe edge by snowmobile or dog sled and then use boats to go beyond the edge into the Arctic Ocean. These boats, kept close to camp, provide a safety measure against the possibility of the campsite floating away.

Graham Dickson

See also Leads; Sea Ice Further Reading

Pielou, E.C., A Naturalist's Guide to the Arctic, Chicago: University of Chicago Press, 1994

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