World Ocean Census - Extract 13 - Polar opposites, differences in the ice oceans

3 April 2010

Antarctica and the Arctic are literally polar opposites, but geography is only one of many differences between these regions. Antarctica is a continent surrounded by ocean and virtually covered in ice, while the Arctic is an ocean surrounded by continents and by Greenland. The physical characteristics of these regions create differences in the sea ice found in them. The landmasses that nearly surround the Arctic Ocean serve as barriers to the movement of sea ice – hence, making it not as mobile as the sea ice surrounding Antarctica. Arctic sea ice does, however, shift and move within its ocean basin; the floes tend to bump into and pile up on one another, forming thick ice ridges. These converging ice floes help to make Arctic ice thicker than the unconstricted sea ice found in the Southern Ocean off the coast of Antarctica.

Part of the sea ice science team on the U.S. Coast Guard cutter Healy is lifted to the ice in the Canada Bassin during a Census expedition to this Artic region in 2005. Courtesy of The Hidden Ocean, Arctic 2005 Exploration

The thickness of the Arctic ridge ice means that some of the ice stays frozen during the summer melts and continues to grow during the following autumn. It is estimated that of the 15 million square kilometers (5.8 million square miles) of sea ice that exist during winter, on average 7 million square kilometers (2.7 million square miles) remain at the end of the summer melt season. These figures are being watched closely as global temperatures warm.

Southern Ocean sea ice forms ridges much less often than sea ice in the Arctic. Also, not being bounded by land to the north, the ice floats into warmer waters, where it eventually melts. Unlike in the north, almost all the sea ice that forms during the Antarctic winter melts during the summer. During the winter, up to 18 million square kilometers (6.9 million square miles) of ocean is covered by sea ice, but by the end of summer only about 3 million square kilometers (1.1 million square miles) remain.

Because the sea ice in the waters surrounding Antarctica is newly made each year, it is also less thick than Arctic sea ice. Antarctic ice is typically 1 to 2 meters (3–6 feet) deep, as opposed to Arctic sea ice, which most often reaches depths of 2 to 3 meters (6–9 feet), and in some areas up to 4 to 5 meters (12–15 feet).

Land inhabitants also vary between these two regions. For example, polar bears live only in the Arctic. No terrestrial mammals live in Antarctica – except for the occasional human researcher or tourist – while the land surrounding the Arctic Ocean hosts several: reindeer, wolves, muskoxen, hares, lemmings, foxes and humans. The Arctic is home to more than a hundred bird species, while less than half that number choose to live on the southernmost continent of the planet.

Regardless of their many differences, from ice composition to the species that inhabit them, the polar ice oceans share a common challenge: adapting quickly as temperatures rise and conditions change in these fragile ecosystems.

Text and images reprinted with permission from World Ocean Census: A Global Survey of Marine Life by Darlene Trew Crist, Gail Scowcroft and James M. Harding Jr., Firefly Books, 2009

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