Drift Ice

IN THE WORLD'S polar regions, ice that floats on the water's surface is termed drift ice. Drift ice is named for its tendency to be carried by wind and currents. Drift ice that is forced into a single mass is called pack ice. The two major ice pack regions in the world, accounting for the majority of the ocean drift ice, are the Arctic and Antarctic ice packs. Increasing water and air temperatures are causing this ice to melt. The extent of this ice depletion by climate change is unknown. Further, the impact of these changes on ice-dependent species, in the long-term, is not clear. Drift ice plays a critical role in climate and ecosystem habitats. The ice originates from the freezing of seawater and can be of varying size and shape. The extent of regions that are covered in potential drift ice (sea ice) during the past 30 years has significantly decreased in the Arctic. However, researchers suggest that while some Antarctic areas are decreasing in ice cover, others are actually on the increase. While the [Page 330]future of drift ice is uncertain, climate models predict a continual decrease in the Arctic regions and a comparable decrease in the Antarctic regions.

Some of the polar regions' most sensitive macrofauna, including birds, seals, penguins, and polar bears, are dependent on drift ice as platforms for rest and hunting, and as sources of food.

The annual fluctuation in Arctic ice ranges from 4.35–9.32 million sq. mi. (7–15 million sq. km.), from the end of summer melt to its peak at the end of winter, respectively. The sea and drift ice area surrounding the Antarctic continent, similarly, range from 1.86–11.18 million sq. mi. (3–18 million sq. km.) during the same seasonal fluctuation. Seasonal ice can range in thickness from 3.28–6.56 ft. (1–2 m.), compared to the typically much thicker permanent ice that does not melt during the summer. The area of ice that does not melt during the summer is gradually decreasing.

Drift ice contributes significantly to the albedo of the Earth's surface, or its reflectivity. High albedo reflects more of the Sun's energy, keeping the Earth cooler, noindent whereas low albedo, particularly with decreasing ice, permits absorption of the Sun's energy by the oceans, which hold the heat and, ultimately, warm the Earth. Snow-covered drift ice contributes even more significantly to a high albedo, but is becoming rare during the summer melt season, when solar energy is greatest.

The contribution of drift ice to the livelihood of humans and animals is significant. Drift ice is a keystone contributor to local and regional food webs. Any changes in ice densities impact tiny microorganisms, including algae and zooplankton, which are dependent on the ice for nutrients and shelter. Ice algae are the primary producers in ice-associated food webs. As primary producers, they are critical to the survival of all higher-level organisms. Ice habitats are critical for the juvenile life stages of many microorganisms, such as zooplankton, which are dependent on these algal and bacterial populations for survival. Fish seek [Page 331]shelter under the drift ice and feast on the abundant zooplankton. Some of the polar regions' most sensitive macrofauna, including birds, seals, penguins, and polar bears, are dependent on this floating ice as platforms for rest, hunting, and a source of food; many feed on the microorganisms and fish found just under the drift ice.

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