The United States Antarctic Research Report to the Scientific Committee on Antarctic Research (SCAR): Number 32 - 1990 (1991)

Possessing the world's largest and most intense climate regime, Antarctica appears to be important in long-term climate variability. During this century, scientists have studied regional climate regimes and unique aspects of the continent's weather. From this research, they have come to understand the major seasonal features of atmospheric circulation, the radiation and energy balances, the nature of katabatic winds, and the transport of gases and aerosols. Such data have been essential for understanding the causes and dynamics of the recently recorded seasonal ''ozone hole'' that has been growing above Antarctica during the last decade. Continuing these investigations, scientists are studying the interaction of solar radiation with snow and ice surfaces find its effect on the energy budget that controls the continent's climate, the relationship between events and conditions in the antarctic atmosphere and global events, and the region's role in global climate change.

Since 1986, U.S. investigators have probed and monitored the changes that are occurring in the ozone layer above the antarctic stratosphere. Although they agree that chlorine, produced by anthropogenic chlorofluorocarbons, is a major cause of the depletion that occurs each spring, the role and impact of atmospheric phenomena, climate dynamics, and other atmospheric constituents remain unclear. These questions now are their focus: How do dynamic processes of the upper atmosphere influence the depletion, what physical properties of polar stratospheric clouds enhance the chemical reactions that destroy ozone, and what other aerosol compounds contribute to the process? Answers to these and other questions are critical not only for understanding antarctic (and arctic) atmospheric and climatic changes but also for determining the global effects of these changes and processes.

For upper atmosphere, solar, and astronomical research, Antarctica is a unique platform from which researchers probe the earth's near-and far-space environment, the nature of stellar and solar activity, and solar-terrestrial effects on humans and the environment. Because the antarctic continent encompasses a wide range of geomagnetic latitudes, scientists can study the plasmapause (the internal magnetospheric boundary), the magnetospheric cusp, and the auroral zone. For more than a decade, solar and stellar astronomers have used the geographic South Pole for observations because it combines continuous daylight (during the austral summer) and long periods of clear weather with high altitude, low humidity, and low effective day temperature. The success of these investigations has drawn more astronomers and astrophysicists to the South Pole. These investigators have found that from this site they can probe the mysteries of the beginning of the universe and the nature of cosmic radiation. Data from these studies and others help describe how solar energy enters the outer terrestrial environment and reaches the atmosphere, how disturbances associated with the transfer of energy propagate to and affect the planet's surface, and how matter in the universe formed into galaxies and clusters of galaxies.

The vivid contrasts and unique characteristics of antarctic marine, freshwater, and terrestrial life have long attracted biologists to the southern continent and the surrounding oceans. Here, the oceans constitute one of the world's most productive

marine regions, while scattered, ice-free areas on the continent support biota of a limited number of species that have adapted to the extreme dry and cold. Because they have identified and quantified much of Antarctica's marine and terrestrial life, biologists are now focusing on the behavior, evolution, and adaptations of these biota and on special factors that drive and maintain these ecosystems. Biologists are studying how these environmental factors-particularly large, dynamic sea-ice zones, near-constant sea temperatures close to the continent, and arid cold and nutrient-poor terrestrial areas-have combined with the continent's isolation to generate special adaptations and interactions between species. With the discovery of the seasonal depletion of ozone above Antarctica, biologists are turning their attention to how marine and terrestrial organisms respond to increased exposure to ultraviolet (UV) radiation. Understanding how antarctic flora and fauna interact has taken on a new significance in the last decade. Without such information, scientists cannot evaluate how life on the continent and in the oceans is responding to such environmental changes as decreased ozone levels that enhance exposure to ultraviolet radiation. These investigations also help scientists to understand how humans are affecting these ecosystems and to hypothesize on the long-term effects of human habitation in this remote region. Conversely, other investigators are beginning to look at the physical and psychological effects of this environment on humans, since here they can find features-isolation and a harsh physical environment—that parallel life in outer space.

Surveying, mapping, and description of most geologic features in Antarctica have enabled geologists during the last 30 years not only to understand regional geology and geophysics but also to address topics that apply to other areas of the world. Antarctic data have supported such theories as plate tectonics and the existence of the ancient supercontinent Gondwanaland and have helped to solve more fundamental problems, including mountain-forming processes and marginal-basin evolution. With most reconnaissance work completed, geologists and geophysicists focus on the role of the south polar region in global geodynamics, the evolutionary history of endemic marine and terrestrial biota, and Antarctica's role in the evolution of ocean circulation. Special considerations include investigating the tectonic relationship of West Antarctica and other areas of the world to learn more about the nature of Gondwanaland before it broke up, probing past environments through the study of fossil data, and collecting for further study the large number of meteorites that have been concentrated on the surface of the antarctic ice sheets.

Antarctica's ice Sheet covers 97.6 percent of the continent in thicknesses up to 4.8 kilometers. Its history-derived from ice cores, the terrestrial geologic record, and the marine sedimentary record-provides information about climate and atmospheric constituents and their variation over time. By studying the continent's glacial history, glaciologists, geologists, and others learn about the timing of northern and southern hemisphere glaciations, global ocean circulation, ocean boundary changes, and the dynamic response of ice to changes in the atmosphere. Deep ice cores taken from the east antarctic ice sheet have provided a 160,000-year record of climate change, while data from ice-free regions enable glacial geologists to create models of ice-sheet fluctuation and soil development. With data from radio-echo sounding and doppler-satellite

positioning, glaciologists and geophysicists have measured the thickness of the ice sheets, learned about the internal layering of ice sheets, and determined the velocity of ice movement. With such data as these, they can better understand the relationship of ice and climate, the stability of Antarctica's ice sheets, and the potential impact of these ice sheets on global sea levels.

The Southern Ocean is important for understanding the history of the world's oceans, changing oceanic conditions, and climatic and glacial history. Physical and chemical processes occurring in the Southern Ocean have a central role in the composition and structure of the world's oceans. Because large-scale heat exchange at the surface overturns the water column and mixes trace constituents, these waters are major sources of the world's intermediate and deep water masses. The Antarctic Circumpolar Current, the world's largest ocean current, affects global ocean circulation, and the annual change in sea-ice cover-from one million to eight million square miles-influences energy transfer. Ocean scientists probe the relationship between oceanic and atmospheric circulation systems and the physical basis for biological productivity; determine the dynamics of formation and distribution of water masses, sea ice, and currents; and investigate the relationship between the Southern Ocean and climate. The complex structure of the seafloor presents fundamental problems in geology and geophysics. The detailed sediment record of changes in the antarctic ice sheet enables geologists to learn more about the continent's glacial history and about changes brought about by the breakup of Gondwanaland.