INTRODUCTION:

Dr. Cornelius W. Sullivan
Director, Office of Polar Programs, National Science Foundation, Arlington, VA

SPEAKERS:

Dr. William R. Fraser
Biology Department, Montana State University, Bozeman, MT

Dr. Deneb Karentz
Departments of Biology and Environmental Science, University of San Francisco, San Francisco, CA

Overview

Dr. Fraser and Dr. Karentz have concluded the following regarding the impacts of ozone depletion and climate change in the Antarctic: 1) Changing patterns of snow deposition and melt are affecting summer nesting habitats of penguins in the West Antarctic peninsula by producing a mismatch between the availability of breeding habitat and the requirements of penguins at various stages in their breeding cycle; 2) these changes are consistent with there having been warming in certain regions of the West Antarctic on the order of 4-5�C, which are values generally consistent with observations and model predictions; 3) those Antarctic species found at the periphery of their breeding ranges are most likely to undergo pronounced changes due to climate change; 4) Antarctic marine organisms have different sensitivities to UV exposure; 5) the amount of biological damage to Antarctic marine organisms due to UV-B radiation is directly correlated to the level of ozone depletion; 6) increased levels of UV-B radiation in the Antarctic can, and do, result in impairment of metabolic processes, decreases in growth, reduction in reproductive potential, morphological abnormalities, genetic damage, and death; and 7) UV-induced damage to marine organisms can further lead to the disruption of entire ecosystems and food webs�therefore, the availability of food resources for humans and other ecosystems.

Long-Term Changes in Certain Antarctic Predator Populations: Evidence of Climate Warming in the Western Antarctic Peninsula

It is estimated that a century ago the number of baleen whales feeding in the Antarctic during summer totaled about one million, with a biomass of 43 million tons. These whales fed primarily on a small crustacean, the Antarctic krill, taking an estimated 190 million tons annually. By the 1930s, commercial whaling had reduced the whale population to about 340,000 individuals, and today the current biomass probably does not exceed 7 million tons, or about one-sixth of the initial stock.

A central tenet of Antarctic ecology holds that the depletion of baleen whale stocks resulted in a "krill surplus." Documented increases in the abundance of krill-dependent predators such as seals and penguins following the collapse of whale stocks have thus been attributed to the effects of competitive release, or the idea that, without whales, other predators benefited from the increased availability of krill. Although this hypothesis has been one of the dominant elements guiding the interpretation of data related to Southern Ocean food web dynamics, close inspection of the long-term population trends of some of these predators has revealed patterns that are inconsistent with this model.

These trends, based on two ecologically similar penguins (Chinstrap and Adelie) found on the Antarctic Peninsula, suggest these species are tracking the effects of a warming trend that is affecting the availability of critical winter and summer habitats. The suspected mechanism appears to involve a decrease in the frequency of cold years with heavy sea ice, which represents critical winter habitat. Changing patterns of snow deposition and melt, perhaps related to the absence of winter sea ice as well, are also affecting summer nesting habitat, producing a temporal mismatch between the availability of breeding habitat and the requirements of penguins, for example, at various stages in their breeding cycles. These observations support the predictions of a number of climate model studies with respect to where pronounced climatological�hence ecological changes�are likely to occur (polar environments), what species will be affected (those found at the periphery of their breeding range), and what biophysical processes may be involved (the disruption of evolved natural history patterns by changing the timing of physical events). These observed physical changes, as well as changes in patterns of behavior, are consistent with expectations of the consequences of the observed regional increase in mid-winter temperatures of 4-5�C over the past half century.

Ecological Considerations of Antarctic Ozone Depletion

Global-scale ozone depletion attributed to anthropogenic pollution of the atmosphere was predicted by scientists more the 20 years ago. Ozone is a natural component of the Earth's atmosphere, and ozone specifically absorbs in the UV portion of the solar spectrum. Even under a "normal" ozone column, harmful UV-B radiation passes through to the Earth's surface. Ozone depletion results in an increase in the amount of biologically harmful UV-B radiation that reaches the Earth's surface and that penetrates into the surface waters of the oceans.

UV-B is biologically harmful, primarily because UV-B is absorbed by key biological molecules such as nucleic acids (DNA) and proteins. Absorption of UV causes structural damage to these molecules, changing their physical shape and interfering with the specific functions they provide for life. Dr. Karentz and her colleagues have observed and documented, for example, that increased levels of UV-B radiation in the Antarctic provoke a range of changes in marine organisms, such as impairment of metabolic processes, decreases in growth, reduction in reproductive potential, morphological abnormalities, genetic damage, and death. Thus, the evidence suggests that UV-induced damage to specific organisms can initiate various degrees of disruption in marine ecosystems, upsetting the balance between organisms and their environment.

Research conducted in the Antarctic indicates that the amount of biological damage to marine organisms is directly correlated to the level of ozone depletion. It has also been observed that Antarctic organisms have differential sensitivities to UV exposure such that a dose of UV that is lethal to one species may only cause impairment in another. The degree of tolerance is dependent on 1) the effectiveness of protective strategies that serve to minimize damage by reducing exposure to UV-B, and 2) repair mechanisms that can correct UV-B induced damage. The combination of protection and repair capabilities varies among species and will influence survival, growth, and reproductive success under UV-B stress. Because each species responds differently, shifts in species composition (biodiversity) are expected under an increased UV-B regime. Even subtle alterations in the quantity or quality of food sources (phytoplankton and krill) can ultimately affect the larger Antarctic consumers such as penguins, seals, and whales. Because the Antarctic marine ecosystem is directly linked to the rest of the world's oceans, changes in the Antarctic region can initiate changes in the rest of the biosphere. We need, therefore, to understand better what these changes might be and what impacts they could have on humans and other ecosystems.