Summary

Antarctica is covered by two ice sheets which have coalesced to form the largest ice body on Earth. There is no melting in the continental interior, and the slowly accumulated ice flows towards the coast in outlet glaciers and ice streams along the margins of the plateau. In areas where the flow is blocked by mountains, ablation of the ice favours the concentration of well-preserved meteorites. The scientific community is also greatly interested in the origin and palaeoclimate of subglacial lakes, in the possible microbial life they contain, and in microbes inhabiting the Antarctic ice sheets and permafrost. The most striking findings of research on Antarctic is the assessment of relationships between changes in atmospheric composition and past climate change. Ice records extend to the past four glacial-interglacial cycles, and progressively longer records are recovered through coring of different domes.

A very small percentage (about 2 %) of the Antarctic surface is free of ice and snow in summer. Most ice-free areas have emerged from the retreating ice in the past few thousand years. Apart from nunataks or the slopes of the Transantarctic Mountains, most of these areas are distributed along the coast; they often lack moraines and glacial deposition typical of deglaciated areas of the Northern Hemisphere, because the deposition of materials in Antarctica occurs in the sea beneath ice shelves or at glacier snouts. The marked latitudinal and altitudinal (inland from the coast) gradient of temperature and water availability determines strong spatial variations in the chemical weathering of rocks and soil formation processes. The southernmost ice-free areas are cold deserts with few developed soils, often encrusted with water-soluble salts. Podzols with low salinity and accumulation of organic matter occur at higher latitudes in Wilkes Land, and active chemical weathering processes with abundant clay-sized materials occur in soils of the Antarctic Peninsula. Ephemeral streams fed by melting ice and/or snow banks flow for some weeks or months in summer, and they may feed small ponds or subglacial and sub-aerial lakes. Most lakes lack outlets and are therefore the main sink for water and solutes from the surrounding catchment area. The climatic gradient and particularly the bioavailability of water influence the abundance and diversity of terrestrial organisms. Although there are few species of cyanobacteria, diatoms, chlorophytes, fungi and lichens in the southernmost rock outcrops of continental Antarctica (at about 86-87° S), well-developed cryptogamic communities and some species of terrestrial microinvertebrates occur further north in sheltered and wetter coastal habitats of the McMurdo Sound region. Cyanobacteria are the most widespread organisms in freshwater ecosystems, and the mats overlying sediments host communities of cyanophytes, diatoms, bacteria, yeasts, protozoans, rotifers, nematodes and tardigrades. Greater species diversity and abundance of organisms are found in ecosystems of continental Antarctica at lower latitudes. Milder and wetter maritime Antarctica (Antarctic Peninsula) not only contains cryptogamic vegetation but also two species of native flowering plants, an endemic wingless midge, and several other species of terrestrial and freshwater invertebrates.

In the first chapter we saw that Antarctica plays a very important role in global climate, and that available data and models suggest that polar regions will be particularly affected by warming and changes in the patterns and amounts of precipitation. This chapter emphasises the role of deep ice core records from the Antarctic plateau in providing one of the best temporal accounts of climate change over the last 500,000 years, and the unique opportunities provided by Antarctic terrestrial and freshwater ecosystems in detecting and predicting the possible effects of change, both climate-based and human-induced. Antarctic ecosystems are deemed among the most sensitive indicators of regional climate change and reliable models of change in more complex ecosystems elsewhere. Some changes, such as the collapse of ice shelves, enhanced melting of ice, and colonisation of newly exposed substrata by cryptogams and two species of vascular plants, are occurring in zones of the Antarctic Peninsula more affected by the regional warming trend.

In conclusion, Antarctic ice sheets and glaciers, sub-glacial lakes, and terrestrial and freshwater ecosystems are very important research sites for a variety of scientific investigations and for addressing global-change issues. Several international research programmes have been developed with the conviction that the value of the expected research findings will compensate for the potential environmental impact and high costs. Increasing difficulties in obtaining funds for complex research beyond the interests of single nations, and concern about the impact of human activity in Antarctica require the development of collaborative multidisciplinary research in a few key areas of Antarctica.

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