Ice stream bed topography contains key evidence for the ways ice streams interact with, and are potentially controlled by, their beds. Here we present the first application of two–dimensional Fourier analysis to 22 marine and terrestrial topographies from 5 regions in Antarctica and Canada, with and without mega-scale glacial lineations (MSGLs). We find that the topography of MSGL-rich ice stream sedimentary beds is characterized by multiple, periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters. This periodic topography is consistent with the idea that instability is a key element to the formation of MSGL bedforms. Dominant wavelengths vary among locations and, on one paleo ice stream bed, increase along the direction of ice flow by 1.7±0.52% km-1. We suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening, even under potentially steady ice stream geometry and flow conditions. The amplitude of MSGLs is smaller than that of other fluvial and glacial topographies, but within the same order of magnitude. However, MSGLs are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction. This study represents the first attempt to automatically derive the spectral signatures of MSGLs. It highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution.
The research was funded by the NE/J004766/1 UK NERC New Investigator and a SAGES PECRE grants awarded to MS. The Amundsen Sea Embayment multi-beam data were acquired on cruise JR141 of the RRS James Clark Ross in 2006 (PI: R. Larter, British Antarctic Survey). The Pine Island multi-beam data were acquired on cruise OSO0910 (Chief scientists: J. Anderson, Rice University, and M. Jakobsson, Stockholm University). The Marguerite Trough multi-beam data were acquired on cruises JR59, JR71, JR157 and NBP0201. This research would not have been possible without the hard work of scientists and crew during these research cruises. John Anderson and Martin Jakobsson are thanked for providing easy access to the Pine Island bathymetries. We would like to thank John Shaw,
Roger Hooke, an anonymous reviewer and the Editor, Bryn Hubbard, for their constructive comments and suggestions that have greatly improved the original manuscript. Underlying bathymetric/topographic data are available by request to the PI/chief scientists of the respective cruises/LIDAR acquisition programs. The spectral results can be accessed by request to T. C. Bartholomaus (email@example.com) or M. Spagnolo (firstname.lastname@example.org).
- ice stream
- mega-scale glacial lineations
- subglacial beforms
- spectral analysis
- pattern formation