Uncovering the footprint of former ice streams off Antarctica

Antarctic ice sheets and ice caps have been expanding and contracting following global climatic cycles. The last time the Antarctic ice cover peaked, at least in Western Antarctica, was ca. 21 ky ago during the Last Glacial Maximum (LGM). The strong warming (nearly 2.8°C) over the past 50 years, and the yearly recent collapse of limited portions (hundreds to a few thousands of square miles per event) of ice shelves around the Antarctic Peninsula have brought to the headlines the debate about the potential collapse of the West Antarctic Ice Sheet (WAIS) in the near future under the influence of global warming. Such a catastrophe would substantially contribute to global sea level rise (a resulting 5 m increase is expected); alter water mass conditions, circulation, and productivity around Antarctica and in the world ocean; and modify the Earth's climate.The economic,social, and ecological impacts of these changes would depend greatly on the rate at which they might take place [Bindschadler, 1998” . A detailed knowledge of the past extent of ice sheets and the timing of their advances and retreats thus becomes essential to quantify the rates of change and to properly assess the future stability of the WAIS and nearby ice caps. The stability of ice sheets is largely dependent on ice drainage, which mostly occurs via ice streaming along glacial troughs. Ice streams are thus a key element to solve the puzzle linking ice sheet stability, sea level rise, and climate change at a global scale

Diversity and biogeography of the Antarctic flora

Aim To establish how well the terrestrial flora of the Antarctic has been sampled, how well the flora is known, and to determine the major patterns in diversity and biogeography. Location Antarctica south of 60°S, together with the South Sandwich Islands, but excluding South Georgia, Bouvetøya and the periantarctic islands. Methods Plant occurrence data were collated from herbarium specimens and literature records, and assembled into the Antarctic Plant Database. Distributional patterns were analysed using a geographic information system. Biogeographic patterns were determined with a variety of multivariate statistics. Results Plants have been recorded from throughout the Antarctic including all latitudes between 60°S and 86°S. Species richness declines with latitude along the Antarctic Peninsula, but there was no evidence for a similar cline in Victoria Land and the Transantarctic mountains. MDS ordinations showed that the species composition of the South Orkney, South Shetland Islands and the north western Antarctic Peninsula are very similar to each other, as are the floras of different regions in continental Antarctica. However they also suggest that the eastern Antarctic Peninsula flora is more similar to the flora of the southern Antarctic Peninsula than to the continental flora (with which it has traditionally been linked). The South Sandwich Islands has a very dissimilar flora to all Antarctic regions, probably because of their isolation and volcanic nature. Main Conclusions The Antarctic flora has been reasonably well-sampled, but certain areas require further floristic surveys. Available data do, however, allow for a number of robust conclusions. A diversity gradient exists along the Antarctic Peninsula, with fewer species (but not higher taxa) at higher latitudes. MDS ordination suggests three major floral provinces within Antarctica: northern maritime, southern maritime and continental. Patterns of endemism suggest that a proportion of the lichen flora may have an ancient vicariant distribution, while most bryophytes are more recent colonists