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
future of drift ice is uncertain, climate models predict a continual decrease in the Arctic regions and a comparable decrease in the Antarctic regions.
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, 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 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.
Indigenous Arctic peoples are dependent on drift ice and sea ice for subsistence hunting of whales, seals, and fish. Decreases in, and thinning of, drift ice with climate change and warming trends reduce the time annually that these peoples have to hunt. The macrofauna spend less time in areas that are readily accessible to the hunters, decreasing the opportunity for a successful hunt and the feeding their families. These decreases in drift ice may also be beneficial to humans, however, with the opening of channels for new sea routes and potential future economic benefits. Ease of navigation through these areas may increase trade between indigenous peoples.
From a global climate perspective, melting of drift ice is likely to have a significant impact on ocean circulation patterns. Ocean circulation is driven by water density differences (thermohaline circulation). Ocean surface waters freeze, and as they freeze, salt from that water is transferred to the water below, thereby increasing its salinity (drift ice has very low salt content). This causes the surrounding surface waters of the oceans where ice forms to increase in salinity. The drift ice is moved by winds and currents to far-reaching locales, contributing "freshwater" ice melt to these areas. With increased melting of the drift ice, freshwater inputs to coastal areas are increasing, potentially causing submersion and flooding of these coastal zones.
Scientists predict that as the ice thins, seawater circulation patterns will change, potentially impacting the ocean circulation patterns of the entire planet. Biodiversity of microorganisms dependent on the drift ice for habitat and resources will decrease. If the oceans change from primarily ice-covered to primarily open waters, the productivity (phytoplankton) of the regions will increase dramatically, altering the oxygen and nutrients available for other organisms, and shift the food web structure, as ice-algae would no longer serve as the primary producers. Regional macrofauna may be forced to move to new regions, if drift ice is no longer present, or their populations will be significantly diminished. The potential impact of climate change and warming on the distribution of drift ice (as the foundation of sea ice) is a major focus of the 2007-08 International Polar Year research programs.
SEE ALSO: Antarctic Circumpolar Current; Antarctic Ice Sheets; Arctic Ocean; Radiation, Ultraviolet; Salinity; Sea Ice; Sea Water, Composition of.
bibliography. R.B. Alley, The Two-Mile Time Machine (Princeton University Press, 2000); Sebastian Gerland, et al., Ice in the Sea (United Nations Environment Programme, 2007); Reinhard Pienitz, M.S.V. Douglas, and J.P. Smol, Long-Term Environmental Change in Arctic and Antarctic Lakes (Springer, 2004).
Sandra Connelly Rochester Institute of Technology
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.