 | Orcas, or killer whales, have a blubber layer approximately 10 centimeters (four inches) thick to shield their warm-blooded bodies from the cold Southern Ocean. Norbert Wu / www.norbertwu.com |
Nearly frozen, the salty polar seas support a staggering array of cold-loving marine life. To keep their bodies warm, birds have lofty feathers and marine mammals have insulating blubber. Meanwhile Antarctica's cold-blooded fish and invertebrates have evolved special mechanisms designed for the unique challenges of icy water.
How do they thrive in such cold conditions?
To avoid the big freeze, some Arctic and Antarctic fishes evolved a protein that keeps their blood ice-free.
The body temperature of cold-blooded fish depends on their surroundings. In the Southern Ocean, that means a chilly -1.8 degrees Celsius (28 degrees Fahrenheit), which is just above salt water's freezing point.
To survive in ice water, Antarctic notothenioid fishes and Arctic codfishes produce an "antifreeze" protein that keeps ice crystals from forming in their blood. Researchers are tracing the evolution of this protein to pinpoint the date when the ancient polar seas cooled to current temperatures. And genetic researchers have used the DNA code for the fish antifreeze protein to produce fruits and vegetables that are frost resistant.
 | Volcano sponges grow as tall as two meters (seven feet) on the polar sea floor because it is an oxygen-rich environment. © Norbert Wu / www.norbertwu.com |
Changes in latitudes mean changes in magnitude for many species living on the floor of the polar seas. These animals can grow to jumbo sizes.
The special nature of cold seawater enables many polar animals, especially those in Antarctica, to dwarf their temperate, or warm-water, relatives.
Scientists once thought that gigantism was due solely to cold water having a slowing effect on metabolism: animals would live longer and grow larger. But it turns out that dissolved oxygen is a factor that determines the maximum size of an animal, and it is more plentiful in cold salt water than in warm water. In the Southern Ocean, some giant sea spiders can grow appendages up to 30 centimeters (12 inches) in length because their blood has enough oxygen to circulate that far.
 | Emperor penguins survive the winter in Antarctica due to adaptations to cold conditions. Their waddling gait, for example, may not look efficient, but the side-to-side motion lets gravity to do some of the work so energy is not wasted on each step.
Fritz Pölking/Visuals Unlimited |
Many animals slow their metabolisms to conserve energy as a way to survive in cold conditions, but others have even more unique strategies.
It takes a lot of energy to live in cold environments-especially freezing water. Antarctic icefishes have developed their own way to conserve energy: trim extra components from the blood so it takes less energy to make it flow.
Most vertebrates need red blood cells to carry oxygen to different parts of the body. The cells, called erythrocytes, contain hemoglobin, a protein that binds oxygen in the bloodstream. The cold Southern Ocean has a high level of dissolved oxygen, which flows through the skin and gills to fill the bloodstream-without the need for red blood cells.
BY THE NUMBERS: Polar Sea Facts
Antarctic's ice sheet contains 90 percent of the world's ice and 70 percent of world's fresh water. During their respective summers, the North and South Poles remain in daylight for 24 hours a day. Champion divers, Weddell seals can hold their breath for more than 80 minutes and reach depths of 700 meters (2,300 feet). One liter (1.1 pints) of Antarctic sea water can contain 1,000,000 floating phytoplankton. |
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