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Meteorological Abiotic Factors
Arctic temperatures range from 10 degrees Celsius in summer to below minus 30 in winter. Winter has little to no sunlight. Summer has near-continuous daytime but little solar radiation is absorbed because snow and ice are so reflective. Yearly precipitation, mostly snowfall and frost, ranges between 60 and 125 centimeters. Surface winds can exceed 60 kilometers per hour and blow blinding snow. To maintain adequate, constant body heat in these conditions, polar bears have evolved double layers of white fur, small tails and ears and shelter-digging and muzzle-covering behaviors.
Water-Related Abiotic Factors
Polar bears migrate seasonally between the Arctic Ocean's shores and packs of sea ice. Free freshwater is markedly rare in these places, but eating snow and ice is not energy efficient. Polar bears have evolved other strategies for extracting and conserving water. They prefer blubber over muscle tissue because their bodies derive water from the metabolic breakdown of fat. Their urine is very concentrated. Pregnant females minimize their water needs by hibernating in dens. Polar bears have other adaptations to water-related abiotic factors, including their swimming and diving abilities, keen underwater vision, buoyant fat layers and broad paws suited to walking and running on ice and snow.
Biotic Factors
Polar bears are the "apex predators" of the Arctic marine food web -- that is, they are not prey to any other animals, with the exception of humans. However, they depend like all other living beings in their habitat upon the food web's health. Polar bears mostly eat seals they hunt on the sea ice. These seals consume fish, which, in turn, survive on smaller organisms such as plankton. Because the winter lacks sunlight for photosynthesis among plantlike plankton species, highly specialized algae and other "lower" organisms have evolved to survive year-round in the sea ice. The ice algae alone account for more than half of all bioproductivity in the Arctic.
Ecological Threats
Although the Arctic's small human population pollutes relatively little, global environmental problems alter and endanger both biotic and abiotic factors in this once-pristine region. From predominantly distant sources, mercury and the endocrine-disrupting chemicals known as persistent organic pollutants (POPs) have become unusually concentrated in Arctic wildlife, most of all in polar bears, compromising their immune and reproductive health especially. Global warming has greatly thinned and disrupted the seasonal patterns of the sea ice, threatening the entire food web of which polar bears are a part.