 | Landscape: Ice holes
Under sea ice, air-breathing marine mammals hold their breath until they can find places to surface. When gaps and cracks in the thick ice freeze over, Weddell seals use their sharp teeth to reopen breathing holes. As a seal's teeth wear down or break after years of chiseling, the animal can't dig holes and will likely perish. Ice holes give seals and even humans access to the bounty of life below the ice. © Norbert Wu / www.norbertwu.com |
Encircling Antarctica, sea ice covering the Southern Ocean is perhaps the most dynamic system on Earth. This ice layer freezes and melts with the seasons, blanketing 3 million to 20 million square kilometers (1.2 million to 7.7 million square miles). It grows as far as the Polar Front-a "boundary" that forms where the cold Southern Ocean meets warm surrounding bodies of water. Sea ice plays a large role in defining the polar ecosystem, including migration patterns of many marine birds and mammals.
Below a blanket of ice, Antarctica's Southern Ocean teems with life. Most exists in pockets along the interface between the ice and the sea, where tiny algae cycle nutrients through the ocean and provide food for both free-swimming and bottom-dwelling animals. Ice algae attract krill by the thousands, which lure whales, fish and penguins to the ice edge. Seals hunt for tasty fish and penguins, while orcas will lunge for the seals. A veritable feast!
Life abounds in the icy ocean habitat surrounding Antarctica.
This frozen environment supports a wide range of species, including some 120 fishes, 45 sea birds, 20 squids and numerous whales, penguins and seals. But a key to the entire system is a crustacean the size of a large shrimp: krill. Large masses of krill provide meals for huge baleen whales and smaller penguins alike. Climate changes threatening krill populations could topple the entire food chain.
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