The Gamburtsev mountains and the origin and early evolution of the Antarctic Ice Sheet

The glaciation of Antarctica The manner in which the Antarctic ice sheet first formed, at a time of rapid global climate change about 34 million years ago, has been the subject of considerable speculation. Several lines of evidence point to central Antarctic mountain ranges as the site of the initial ice sheet, but our knowledge of the present ice-sheet topography is highly restricted in the very zone where ice-sheet initiation is most likely: along the subglacial Gamburtsev mountain range at the centre of the present ice sheet. Now a detailed survey and analysis of the morphology of the Gamburtsev mountains has been performed, based on an ice-penetrating radar study conducted over two seasons. The data reveal a mountain landscape initially incised by rivers, then over-deepened by ice movement. The topography — beneath up to 3,000 metres of ice — resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago, when mean summer temperatures were about 3 °C. The nature of initial glaciation on Antarctica about 34 million years ago is a mystery. Results from an intensive radar survey now show that the Gamburtsev mountains at Dome A, at the centre of the present ice sheet, were initially incised by rivers and then subsequently overdeepened by ice movement; this is suggestive of topographical development before 34 million years ago, when mean summer temperatures were about 3 °C. Ice-sheet development in Antarctica was a result of significant and rapid global climate change about 34 million years ago 1 . Ice-sheet and climate modelling suggest reductions in atmospheric carbon dioxide (less than three times the pre-industrial level of 280 parts per million by volume) that, in conjunction with the development of the Antarctic Circumpolar Current, led to cooling and glaciation paced by changes in Earth’s orbit 2 . Based on the present subglacial topography, numerical models point to ice-sheet genesis on mountain massifs of Antarctica, including the Gamburtsev mountains at Dome A, the centre of the present ice sheet 2 , 3 . Our lack of knowledge of the present-day topography of the Gamburtsev mountains 4 means, however, that the nature of early glaciation and subsequent development of a continental-sized ice sheet are uncertain. Here we present radar information about the base of the ice at Dome A, revealing classic Alpine topography with pre-existing river valleys overdeepened by valley glaciers formed wh