A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes

Abstract

The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ∼34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.

Land-ice elevation changes from photon-counting swath altimetry: first applications over the Antarctic ice sheet

“…Wilkes Land and the adjacent George V Land of the IndoPacific sector of the Southern Ocean adjoins a region of the East Antarctic ice sheet underlain by deep subglacial basins that bear evidence of considerable past retreat (Jordan and others, 2010;Young and others, 2011) and current subglacial activity (Smith and others, 2009;Wright and others, 2012;McMillan and others, 2013). As these basins are grounded below sea level and slope toward the interior, the overlying ice sheet is susceptible to rapid retreat through the marine ice-sheet instability if restraining forces on the sides and front are released, in particular from bounding ice shelves (Schoof, 2007).…”

“…ICECAP used a long-range ski-equipped DC-3T modified for aerogeophysics by the University of Texas, and equipped with ice-penetrating radar, gravimeter, magnetometers and laser altimeters to investigate the geometry (Roberts and others, 2011), long-term history (Young and others, 2011), stratigraphy (Cavitte, 2011) and subglacial hydrology (Wright and others, 2012) The ICECAP geophysical system was installed on the aircraft at the McMurdo seasonal sea-ice runway at the start of each field season. Installation was followed by a calibration flight involving multiple crossovers over flat ice.…”

Ice flow models and glacial erosion over multiple glacial–interglacial cycles

“…Regions like the Gamburtsev Subglacial Mountains underneath the East Antarctic Ice Sheet (Young et al, 2011) illustrate that, no matter how large and thick ice coverage might be, as in Simulation 2 (Fig. 4), if the basal temperature is regularly below freezing, there will be little modification of subglacial topography because there is no sliding.…”

Weak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica

“…The latter approach has also been used to study large-scale bed roughness of ice sheets (Young and others, 2011;Ross and others, 2012). Calculating the rms deviation for a range of horizontal length scales produces a bed roughness 'spectrum' analogous to that produced by spectral methods.…”