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

When the inward gravitational pressure of a star exceeds the outward radiation of energy, the star's core collapses. Violent shock waves, moving from its core to the surface, blast away the outer layers of the star. This spectacular release of energy is a supernova.

Supernovas, which briefly give off amounts of energy that can rival the energy output of an entire galaxy, may trigger the birth of other stars, provide the energy and physical environment needed to synthesize elements that are heavier than iron, and have a part in redistributing heavy elements in the interstellar medium-gaseous and dust materials between stars.

At the time of the "Big Bang," the event that many believe formed our universe, only hydrogen, deuterium (heavy hydrogen), and helium formed. All other chemical elements, according to theory, must have been formed by processes occurring in stars, but a star that is in equilibrium does not generate enough energy or have conditions extreme enough to cause the synthesis of heavy elements. Only tremendous amounts of energy and extreme conditions like those resulting from a supernova can complete nucleosynthesis-the various processes by which the nuclei of new elements are formed from other elements.

In February 1987 the first observations of Supernova 1987A were made. This supernova is the first to occur close to Earth since the invention of the telescope. To learn more about this event, astronomers and astrophysicists launched a high-altitude, instrumented balloon from McMurdo Station in 1988. They selected Antarctica because the southern continent offered advantages not found at other sites. An important advantage is that radiation levels in the atmosphere above Antarctica more closely approximate those in space than levels above northern areas.

The success of this project encouraged the launching of a second instrumented balloon during the 1989-90 austral summer. A 26.4-million-cubic-foot, high-altitude balloon was launched near McMurdo Station. Investigators hoped that the balloon would stay aloft for 14-20 days. After two failed launches, a 28-million-cubic-foot balloon was launched in December 1990 and followed a circumnavigation of the South Pole at approximately 78°S latitude and an altitude of 120-130 km.

Supernova 1987A appears to be a Type II supernova, which occurs when the core of a star with a mass eight times greater than the mass of the Sun has been fused to iron. The energy generated causes gravitational collapse. Astrophysicists believe that the core becomes a neutron star and that as the external layers are blasted away, isotopic nickel-56 and nickel-57 are produced. Because each radioactive isotope produced by explosive nucleosynthesis has a unique gamma-ray signature, investigators hope to be able to trace gamma-ray emissions that show the decay of nickel-56 to cobalt-57 to iron-57. By tracing this path, they will be able to better determine whether Supernova 1987A is typical of events that cause galactic nucleosynthesis. They will also search for X-ray emissions from Supernova 1987A to determine if it has become a neutron star as many scientists anticipate it will.

The balloon flight offered opportunities to study phenomena other than the supernova. Focusing on cosmic rays, investigators attempted to define better the

isotopic composition of nickel, iron, manganese, and cobalt in cosmic rays. Such information will help astrophysicists to understand the structure and composition of the interstellar medium, the acceleration of cosmic rays, and the conditions under which heavy elements are formed in supernovas and other astrophysical objects.

Continuing research begun in 1986, three science teams monitored changes in the ozone layer above Antarctica during the late austral spring. Work in previous years has enabled scientists to determine that atmospheric chlorine, derived from man-made chlorofluorocarbons, is a principal component of the chemical cycle that is eating away the antarctic ozone layer. At McMurdo Station, one group launched instrumented balloons to take profiles of ozone and temperature from the ground to an altitude of 29 kilometers (18 miles) to identify where in the air column ozone is being destroyed. A second group measured solar spectra during the spring at McMurdo Station to determine the amounts and concentrations of such atmospheric compounds as hydrochloric acid, nitric acid, nitrogen dioxide, chlorofluorocarbons, ozone, methane, and nitrous oxide in the stratosphere. At Palmer Station, a third group continued to use balloonborne ozonesondes to record changes in depth, vertical extent, ozone-loss rates, and seasonal variations.

At Amundsen-Scott South Pole Station, a lidar-a laser infrared radar with an intense pulsing beam that measures atmospheric discontinuities-was used to determine the vertical motion of the sodium layer about 90 kilometers (56 miles) above Earth. This information will be related to the processes causing the ozone depletion, particularly the dynamics of the climate. A second project at the South Pole focused on the characteristics of polar stratospheric clouds. These clouds, which are made of ice crystals and form at temperatures below -80°C, provide the environment in which the ozone-destructive chemical reactions occur.

Global loss of protective ozone in the stratosphere allows more ultraviolet radiation to reach Earth and has raised concerns about increased human risk of skin cancer and immune-system suppression. But scientists are also worried about the effect of UV radiation on life forms, including the plants and animals that make up the highly productive marine-based food chain of Antarctica, where seasonal depletion of ozone is greatest. In all life forms, the genetic material DNA can be damaged by ultraviolet radiation, but organisms differ in the amount of damage they receive and in their abilities to repair this damage.

Ecosystem-wide effects of UV radiation in Antarctica may not be predictable any time soon. Nonetheless, laboratory studies at Palmer Station reveal nearly one-hundred-fold differences in the amount of genetic damage sustained when various phytoplankton species are exposed to certain wavelengths of light. Diatoms, phytoplankton with glass shells made from silica, were among the most abundant phytoplankton in antarctic waters in September 1988, when the seasonal ozone hole was forming. Investigators exposed nine species of diatoms to middle-wavelength UV light, or UV-B, which is most strongly absorbed by ozone, to evaluate chemical changes in the small building-block molecules of DNA, called nucleotide bases. Unrepaired damage to nucleotide base pairs within genes can impair the finely-tuned regulation and production of cellular proteins, harming or even killing an organism.

Investigators found that some species incurred more mutations to their DNA chains and that some species were better able to persevere after UV exposure. It is possible that the timing and intensity of the ozone hole and the associated increase in penetration by UV-B radiation may reduce populations of some phytoplankton species, allowing other species more resistant to UV-B damage to expand opportunistically their niches. If this happened, the incidence of secondary effects on the health of animal populations higher up the food chain-e.g., krill, fish, penguins, and whales-might depend on how choosy krill and other phytoplankton-eating animals are about the species they graze upon.

To combat DNA damage, phytoplankton, like higher plants and animals (including humans), possess DNA repair mechanisms. Diatom species appear to differ in their reparative abilities as well as their susceptibility to damage. Though UV radiation is damaging to organisms, longer wavelength UV-A light also is required by phytoplankton for one type of DNA repair, called photoreactivation. This mechanism appears to play an important role in the varied rates of DNA repair achieved by diatoms.

Because phytoplankton also require visible light to drive photosynthesis and to mend damage to their photosynthetic systems, many biologists believe that it is important to consider the amounts of all three of these wavelength bands of electromagnetic radiation when examining biological impacts of the ozone hole. The ozone hole does not affect penetration by UV-A or visible wavelengths.

By the end of March 1989-about two months after the Argentine transport ship Bahia Paraiso ran aground in Arthur Harbor near Palmer Station-an estimated 150,000 gallons of diesel and jet fuel had spilled into the ocean. While small relative to major world oil spills, this event could potentially have significant impacts on the biota in the nearly undisturbed area on the Antarctic Peninsula.

A scientific team representing nine institutions from three countries was organized to study the environmental impact of the oil spill. During their month-long stay at the station, the researchers assessed the immediate impact and began a long-term research program on how the oil spill has or may yet affect the plants and animals in the area. The team's objectives were to identify and determine the fate of hydrocarbon compounds, to study the microbial degradation of hydrocarbons, and to observe and record the response of the animal and plant biota to the spill.

The research team predicted that the water-column community should show little if any long-term effects. Because oil may persist in the sediments, the long-term consequences for the benthic plant and invertebrate communities are unclear. It will take years to assess completely the effects on seabirds. Future research will focus on a long-term program of ecosystem recovery.

In the McMurdo Dry Valleys, the ice-free region of southern Victoria Land, freshwater lakes provide unique opportunities to study biogeochemical cycles and biota that have adapted to an extreme terrestrial environment. Scientists studied chemical and biological changes that occur seasonally in Lake Fryxell to obtain new data that can be applied to similar cycles in non-antarctic lakes.

Located in one of Earth's most arid, barren environments, this lake-unlike lakes in other areas of the world-receives minor amounts of organic material and nutrients from glacial meltwater, has an extremely simple seasonal cycle, and is stabilized by a permanent ice cover. However, during the austral summer, enough light penetrates the ice cover to sustain a community of algae and bacteria. This ecosystem is similar to

temperate lakes without plant nutrients but with plentiful amounts of oxygen. Because Lake Fryxell is a closed system, two groups of scientists would be able to determine how carbon, nitrogen, and sulfur are cycled through the lake system. They also studied how constant light in the summer and constant darkness in the winter affect the chemical and biological systems and what interaction occurs among processes that occur in aerobic, anaerobic, and benthic zones of the lake.

West Antarctica is a collage of small tectonic plates that reflect movement during or after the breakup of the ancient supercontinent Gondwanaland. For geologists, understanding the relationship between West and East Antarctica and between West Antarctica and former pieces of Gondwanaland is crucial for understanding ancient environments, the evolution of southern ocean circulation, and the global interaction of tectonic plates.

One team of U.S. and British geologists studied the tectonic evolution of the southern rim of the Pacific Ocean. Another group focused on the relationship between Marie Byrd Land and New Zealand to learn if these two regions were once part of the same tectonic unit. A third team worked in the Ellsworth Mountains, focusing on how and when these mountains were formed. Finally, U.S., British, and New Zealand investigators examined the glacial and volcanic history of Marie Byrd Land.

Polar ice sheets contain a unique record of recent and past climate and of the interactions between climate and the biosphere that influence our environment. Ice cores taken from Antarctica and Greenland offer scientists the opportunity to study the buildup of atmospheric carbon dioxide, oxygen isotopes, methane, lead compounds, chlorofluorocarbons, and trace gases over time periods ranging from one year to several centuries.

In 1984 Soviet and French glaciologists obtained an ice core from the polar plateau near the Soviet station Vostok. This core spans 160,000 years and contains a record of atmosphere and climate change that includes a record of the last global glaciation. During the 1989-90 austral summer, U.S. investigators used samples of the Vostok core to assess, among other things, how levels of organic sulfur vary under changing climate conditions, how the climate and biosphere interacted during the Pleistocene epoch, and how concentrations of methane and nitrous oxide have changed in response to past global warming and cooling.

Scientists know that greenhouse gases (carbon dioxide, methane, and nitrous oxide) and sulfate aerosols affect climate by either absorbing incoming solar radiation or contributing to cloud formation and preventing solar radiation from reaching the earth's surface. Because methanesulfonic acid has no nonliving precursors, it gives a clear chemical signal of changes in oceanic sulfur production and the productivity of the world's oceans-a critical factor in the control of carbon dioxide levels. With data from the Vostok core, investigators will differentiate between organic and non-organic sulfur

aerosols and will determine what levels of cloud-forming molecules existed in ancient climates.

Over short intervals (100,000 years or less), climate is influenced by solar radiation levels, varying concentrations of gases, and other less-well understood factors. By determining the composition of oxygen, nitrogen, and argon trapped in the ice core to learn more about photosynthesis, respiration, and hydrologic process, investigators hope to describe global interactions among the hydrosphere, biosphere, and atmosphere, and to compare past and present measurements of atmospheric nitrogen, in order to understand climate changes that are presently occurring.

Methane and nitrous oxide can have a greater impact on the environment than carbon dioxide. Ice-core data show that during ice ages and colder periods, these gases were present at levels 50 percent lower than those before the Industrial Revolution and about 20 percent lower than today. These changes probably reflect the response of the world's ecosystems to climate changes. Because records from the last 100 to 200 years show that atmospheric levels of both gases have increased dramatically, scientists are concerned about the contribution methane and nitrous oxide will make to global warming. By studying the 160,000-year record in the Vostok core, investigators hope to record how concentrations of these two gases changed in response to past global warming and cooling.