polar seas

The frigid waters of the Arctic and the Antarctic may seem like hostile habitats. But a variety of marine life -- from algae to whales -- is found beneath these frozen surfaces. The ice-cold surface water is constantly mixed with warm bottom water, spreading nutrients throughout the ocean. This endless churning motion is also linked to Earth's climate.

Locations: the Arctic Ocean (near the North Pole) and the Southern Ocean, which surrounds Antarctica
Common Arctic animals: polar bears, walruses, whales, and seals
Common Antarctic animals: fishes, sea birds, whales, penguins, and seals
Threats to these habitats: global warming, overfishing, pollution

Image credits: main image, courtesy of AMNH, Norbert Wu.