Polar bears (Ursus maritimus) are carnivorous marine mammals that prowl the ice sheets and coastal waters of the Arctic region. They have developed several key adaptations to thrive in the harsh cold of their northern habitat, including a thick, insulating layer of fat and a coat of white fur that not only provides camouflage in snow and ice, but also extends to the bottom of their paws to provide additional grip. Polar bears are excellent swimmers because of their elongated bodies and strong front paws, and are able to cross distances of up to several hundreds of kilometers in water. The animals have no natural enemies and primarily hunt for seals along the edges of the ice where their prey surface to breathe, but they are also known to feed on land mammals or the carcasses of whales. After mating in spring, female polar bears set out to gain weight and dig a den in the snow, where they enter a hibernation-like state and give birth in winter, generally to a litter of two cubs. They raise their young for a period of approximately two and a half years without the help of males, boldly protecting them against the elements and threats, such as wolves and other polar bears.
Information sources: National Geographic, WWF
Image: Polar bear roaming sea ice in Nunavut, Canada. Credit: Ansgar Walk, Wikimedia Commons.
Research of biologists published in Global Change Biology indicates that emperor penguins on Antarctica were forced into refugia by extreme cold during the last glacial maximum (~ 19.5 – 16 thousand years ago). By comparing the DNA of fossil emperor penguins with the DNA of living individuals and colonies, the scientists were able to reconstruct the population dynamics of emperor penguins on Antarctica through time. Their results show three mitochondrial clades within emperor penguins at the time of the last glacial maximum, which suggests that these birds were isolated in three small, separate populations and may have survived in refugia such as the Ross Sea. The population sizes of emperor penguins are related to the balance between sea ice available for breeding and open water available for foraging. Sea ice extent around Antarctica was much greater during the last glacial maximum than at present and therefore, reduced food availability resulted in severe losses among populations of emperor penguins.
Journal reference: Younger, J. L., Clucas, G. V., Kooyman, G., Wienecke, B., Rogers, A. D., Trathan, P. N., … & Miller, K. J. (2015). Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum. Global change biology, 21(6), 2215-2226.
Image: Emperor penguin colony foraging along the Weddell Sea, Antarctica. Source: Christopher Michel, Wikimedia Commons.
Emperor penguins (Aptenodytes forsteri) are the largest of all penguins and are adapted to the extreme cold of the ice sheets of Antarctica and the surrounding seas. They are characterized by a black head and backside, with a hint of yellow on their breast and behind their ears. Because of their streamlined bodies and strong flippers, emperor penguins are excellent swimmers, and at sea they can dive to a depth of more than 500 meters, deeper than any other bird. As carnivores, emperor penguins prey on fish, squid and krill, while they are hunted by leopard seals and killer whales as well as large seabirds, which scavenge mainly on chicks. They are very social animals that huddle together in large colonies in order to survive the harsh conditions of their icy environment. Emperor penguins breed in winter and while females go hunting in the Antarctic waters for themselves and their unborn chicks, males keep the eggs warm in brood pouches on top of their feet. Male and female emperor penguins stay together during the full breeding season, but some are even rumored to remain faithful to their partners for life. After an egg hatches, the parents of the newly born chick take turns foraging at sea and raising their chick in the colony.
Information source: National Geographic, WWF
Image: Emperor penguin family on ice along the Weddell Sea, Antarctica. Source: Christopher Michel, Wikimedia Commons.
Climatologists at the University of Southampton have discovered that over the past 19 years, sea level around the coast of Antarctica has risen 2 cm more than the global average rise of 6 cm. They have detected this rapid sea level rise by studying detailed satellite images of an area spanning over a million square kilometers and have attributed it to the melting of fresh water from the Antarctic glaciers and ice shelves, which is further supported by a decrease in the salinity of the surrounding ocean waters. In order to explain these observations, the scientists estimate that a total discharge of approximately 430 Gt of fresh water to the surrounding ocean is required. Furthermore, global ocean circulation model simulations of the effects of melting ice on the Antarctic Ocean closely match their findings.
Journal reference: Rye, C. D., Garabato, A. C. N., Holland, P. R., Meredith, M. P., Nurser, A. G., Hughes, C. W., … & Webb, D. J. (2014). Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge. Nature Geoscience, 7(10), 732-735.
Image: Melting icebergs along the Antarctic Peninsula, Antarctica. Source: Christopher Michel, Wikimedia Commons.