Glaciers are massive ice sheets that persist year-round while icebergs are large floating islands of freshwater ice, broken off from glaciers. They are common to the seas around each pole, and may or may not persist for multiple years. Icebergs play a larger role in the lives of animals than glaciers, as icebergs are more immediately surrounded by the nutrients necessary for life.
Glaciers are fairly devoid of nutrients or conditions that might support life. While birds and large animals such as polar bears might visit a glacier, only a few small, specialized animal are capable of truly living on these massive blocks of snow and ice. These tiny animals include glacial midges, snow fleas, glacial copepods, rotifers and ice worms. These animals are preyed upon by larger animals that occasionally pay a visit to their glacial home. For example, ice worms are preyed upon by snow buntings and other birds.
Iceberg Polar Bears
Polar bears spend much of their time hunting seals in Arctic waters, so it makes sense that they would also spend much of their time living on icebergs. As many as 20 polar bears were observed living on an iceberg off the Arctic Canadian coast, according to the 2012 BBC article "Polar Bear Sanctuary on Iceberg." Polar bear expert and biologist Steven Amstrup told the BBC that this was the first time bears were spotted living in large numbers on an iceberg out at sea. The bears may have found refuge on icebergs as a consequence of decades of being hunted by humans on dry land.
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Ice Floe Penguins
Adélie penguins are having to adjust their behaviors in response to recently changing sea ice conditions, according to a 2014 study conducted by a team of French, American, and South African researchers and published in the journal PLoS ONE. Sea ice is different from glacier ice-- sea ice is frozen seawater and glacier ice is frozen freshwater from precipitation. Like icebergs and glacier ice, pieces of fast sea ice can break off and become floating chunks of ice; these are called ice floes. Adélie penguins rely on all manner of ice floes for foraging, migrating, moulting and resting. These penguins prey on the species that live on the underside of ice floes, such as krill. The penguins also prey on the predators of these species, such as Antarctic silverfish. The study reveals that the penguins are, fairly successfully, changing their habits due to changing sea ice conditions.
Icebergs are also highly important to Arctic seals. Harbor seals are much safer from predators when they haul out, or take a break from the water, on icebergs as opposed to on land, according to the Alaska Department of Fish and Game in its website post "Harbor Seal Research." In addition to using them as a refuge from predators, harbor seals also use icebergs for giving birth. Weddel seals living off the coast of Antarctica have been found to be reliant on sea ice, and therefore affected by changing sea ice patterns in recent years.