Antarctic Ecosystems as Indicators of Change

Global climate models predict that polar regions will be affected by air temperature increases and changes in the amount and pattern of precipitation. Changes in temperature (melting and freezing) and precipitation in Antarctic ice-free areas are likely to strongly affect water availability and the distribution and appearance of new, uncolonised areas. Climate amelioration and increased water bioavailability may act alone or synergistically to enhance colonisation and the establishment of local invasive or exotic pre-adapted species (Walton 1990; Watson 1999).

In highly desiccated saline soils, liquid water controls biogeochemical processes, and changes in chemical weathering, salt solubilisation, substrate stability and terrestrial productivity will strongly affect lacustrine ecosystems, which are multiyear integrators of changes in landscape processes. Furthermore, climate changes are likely to affect the limnology of polar desert lakes through changes in the duration and thickness of snow and ice cover (i.e. underwater light availability), and in thermal and chemical regimes, with unpredictable effects on organism abundance and diversity.

Biotic communities in Antarctic cold desert ecosystems are rather simple and fragile, with many species either living at the limit of their range or adapted to cope with extreme environmental conditions. The low species diversity and lack of several functional groups, such as angiosperms in terrestrial ecosystems and macroinvertebrates in aquatic ecosystems, means that the loss or gain of even a single species may strongly affect the integrity and productivity of these ecosystems. Species of sub-Antarctic invertebrates and plants possess sufficient physiological characteristics and ecological plasticity to allow survival in maritime or continental Antarctica, and climate amelioration will increase the pool of potential colonists (Convey 2000). Undoubtedly, Antarctic ecosystems are more sensitive indicators of regional climate changes or colonisation processes than ecosystems at lower latitudes, where responses of biotic communities to external forcing and potential colonists are buffered by more complex biological interactions and feedback processes.

Atmospheric circulation patterns are responsible for the deposition of persistent airborne pollutants from lower latitudes into Antarctic ecosystems (Bargagli 2000). Global warming will probably enhance the contraction of sea ice and the penetration of air masses and clouds into the continent. It cannot be excluded that these changes will increase the deposition of atmospheric pollutants on the continent. Xenobiotic compounds may more severely impair organisms growing in extreme environments than related species growing under less stressful conditions in temperate regions.

All these aspects make Antarctic ice-free landscapes sensitive indicators of regional climate and environmental change, and models of change on a global scale (Walton et al. 1997). In looking to the future of Antarctic ecosystems, the Scientific Committee on Antarctic Research (SCAR 1989, 1993; SCAR/COMNAP 1996) has identified the possible implications of enhanced global warming and the impact of human activity on Antarctic ecosystems as research priorities. As a successor of the SCAR-BIOTAS (Biological Investigations of Terrestrial Antarctic System) programme, a new international research programme SCAR-RiSCC (Regional Sensitivity to Climate Change in Antarctic Terrestrial Ecosystems) has been developed to study responses of terrestrial and freshwater ecosystems to climate change. As an analogy for future climatic and environmental change, research is focused on a variety of sites along a latitudinal gradient, covering about 40° (from the peri-Antarctic islands to southern Victoria Land). To develop a predictive understanding of ecological change, research must address the ways in which ecosystems interact with their environment, the influence of abiotic variables on population performance, and relationships between species abundance and richness.

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