HR: 0800h
AN: C51A-0097    [Abstracts]
TI: The Role of Glacial Erosion in Limiting Ice Sheet Extents
AU: * Jamieson, S
EM: Stewart.Jamieson@ed.ac.uk
AF: University Of Edinburgh, School of GeoSciences, Institute of Geography, Drummond St., Edinburgh, EH8 9XP, United Kingdom
AU: Hulton, N
EM: Nick.Hulton@ed.ac.uk
AF: University Of Edinburgh, School of GeoSciences, Institute of Geography, Drummond St., Edinburgh, EH8 9XP, United Kingdom
AB: We aim to identify and quantify feedbacks between ice dynamics and glacial erosion. Whilst geological and geomorphological evidence indicates that ice sheets generally oscillate in time with orbital forcing, their extents are not necessarily a direct function of the amplitude of this forcing. Benthic δ¹⁸O records document glacial-interglacial fluctuations and indicate that maximum Pleistocene global ice volume occurs around 400 ka. However, geomorphological evidence in a number of regions is contradictory, with the most extensive ice masses often occurring 100's of kyrs prior to peaks in the δ¹⁸O record. For example, the glacial landforms of Patagonia preserve a record of just such behaviour with each successive glacial advance since 1.15 Ma covering an area less extensive than the previous expansion. This implies that other processes are modifying the linkages between ice sheets and climate. We ask: Could glacial erosion of bedrock have caused ice sheets to self-regulate their extents? Ground-breaking experiments by Oerlemans (1984) demonstrated that erosion induced margin retreat was indeed possible. He showed that retreat could be achieved but only where eroding ice streams were smaller in width than the wavelength of lithospheric response. In Patagonia however, the scales of retreat are much larger than this lithospheric wavelength – but could erosion still be an important factor? We use the GLIMMER 3-D thermomechanical ice sheet model (Payne, 1999) with an added erosion component to simulate long-term landscape evolution under theoretical ice sheets (Jamieson et al., 2007). We show that models of glacial erosion can generate feedbacks on a significant scale such that ice sheets can self-limit their extents over periods of 10⁵ - 10⁶ years regardless of the flexural response of the land surface. Erosion around the ELA enables increasingly efficient ice drainage, and the mass balance of the ice sheet thus shifts towards a more negative state. At the same time, the thermal regime of the ice alters and the drawdown and capture of warm ice into ‘streams' causes more focussed selective erosion. The main control on the pattern of retreat is the pre-existing topography, which strongly controls erosion patterns. Ice streams retreat progressively in response to lowering valley floors and the impact of erosion induced self-limiting remains over successive glacial cycles. References: Jamieson, S.S.R., Hulton, N.R.J. and Hagdorn, M., 2007. Modelling landscape evolution under ice sheets. Geomorphology, doi:10.1016/j.geomorph.2007.02.047. Oerlemans, J., 1984. Numerical experiments on large-scale glacial erosion. Zeitschrift fur Gletscherkunde und Glazialgeologie, 20: 107-126. Payne, A.J., 1999. A thermomechanical model of ice flow in West Antarctica. Climate Dynamics, 15(2): 115-125.
DE: 0726 Ice sheets
DE: 0768 Thermal regime
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 0798 Modeling
SC: Cryosphere [C]
MN: 2007 Fall Meeting