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in a glaciated area is the extent to which ice sheets have transformed a preexisting fluvial topography. For 150 years there has been debate between those highlighting the erosive power of ice and those indicating its preservative capacity. In 1848 Charles Lyell, on his way over the formerly glaciated eastern Grampians of Scotland to receive a knighthood from Queen Victoria, wrote in his diary, “Here as on Mt Washington and in the White Mountains the decomposing granite boulders and the bare surfaces of disintegrating granite are not scored with glacial furrows or polished.” Such observations subsequently led to the idea of unglaciated enclaves that escaped glaciation completely (e.g., in Britain: Linton, 1949; and in North America: Ives, 1966). In Antarctica, scientists on the early 20th-century expeditions of Scott and Shackleton debated the issue, with Taylor (1922) arguing that the landscape was essentially glacial in origin but cut under earlier warmer glacial conditions, and Priestley (1909) arguing that glaciers had modified an existing fluvial landscape. The debate has continued; some argue for dissection of the Transantarctic Mountains by glaciers since the Pliocene (van der Wateren et al., 1999) while others point to the important role of fluvial erosion at an earlier time (Sugden and Denton, 2004).

This paper contributes to this debate by outlining the main variables influencing landscape evolution in Antarctica and then developing hypotheses about what might be expected from both a fluvial and a glacial perspective and the interaction of the two.

WIDER CONTEXT

East Antarctica consists of a central fragment of Gondwana and is surrounded by rifted margins (Figure 1). The initial breakup of Gondwana around most of East Antarctica took place between 160 Ma and 118 Ma. The separation of India and Antarctica took place first, while the separation of Australia from Antarctica took place in earnest after 55 Ma. Tasmania and New Zealand separated from the Ross Sea margins at around 70 Ma. West Antarctica comprises four separate mini-continental blocks: Antarctic Peninsula, Thurston, Marie Byrd Land, and Ellsworth-Whitmore, thought to be associated with extensional rifting. The drift of the continents opened up seaways around Antarctica and changed ocean circulation and productivity. A long-held view is that this permitted the development of the Antarctic Circumpolar Current, which introduced conditions favorable for glaciation (i.e., cooler temperatures and increased precipitation) (Kennett, 1977). In addition, recent climate modeling studies have suggested that a reduction in atmospheric greenhouse gases may have played an important role in the triggering of Antarctic glaciation (DeConto and Pollard, 2003; Huber and Nof, 2006). Critical dates for the development of ocean gateways are ~33 Ma, when a significant seaway opened up between Antarctica and Australia (Stickley et al., 2004), and ~31 Ma, when Drake Strait between the Antarctic Peninsula and South America became a significant seaway (Lawver and Gahagan, 2003).

The stepwise glacial history of Antarctica has been pieced together from marine records. Ice sheets first built up at ~34 Ma and their growth was marked by a sudden rise in benthic δ18O values (Zachos et al., 1992). On land on the Ross Sea margin of Antarctica, beech forest similar to that in Patagonia today gave way to scrub forest and this change was accompanied by a progressive shift in clay minerals from smectite, typical of forest soils, to chlorite and illite characteristic of polar environments (Raine and Askin, 2001; Ehrmann et al., 2005; Barrett, 2007). Glaciation for the next ~20 million years was marked by ice volume fluctuations similar in scale to those of the Pleistocene ice sheets of the Northern Hemisphere. These fluctuations are demonstrated

FIGURE 1 The location of Antarctica within Gondwana. The reconstruction shows the fragmentation of the supercontinent at 120 Ma (modified from Lawver et al., 1992).



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