Geomorphic signature of an Antarctic palaeo-ice stream: implications for understanding subglacial processes and grounding line retreat
Abstract
The ability to capture the complex spatial and temporal variability exhibited by ice streams in Antarctica and Greenland at short (decadal) time-scales, remains one of the key challenges in numerical modelling and underlies current uncertainties with predicting future contributions of ice sheets to sea-level rise. This has made ice streams a major focus for current glaciological research, particularly with regard to the processes occurring at the ice-bed interface. Such studies unfortunately, only provide a ‘snap-shot’ of the life-cycle of an ice stream, limited to the last few decades, and so there is a need for complementary investigations of former zones of fast flow in palaeo-ice sheets. The ability to observe directly the former beds of palaeo-ice streams has allowed important spatial and temporal information to be obtained on the processes that occurred at the ice-bed interface and on ice dynamics associated with the evolution of palaeo-ice streams. We present new glacial geomorphological evidence from a marine palaeo-ice stream in Marguerite Bay, Antarctic Peninsula (Ó Cofaigh et al. 2002, 2005). The landform assemblage of this palaeo-ice stream system has been derived from the mapping of over 16,000 glacial landforms from high-resolution multibeam swath-bathymetry and input into a GIS database. Analysis of the spatial distribution and geomorphic relationships between landforms and landform assemblages has revealed a complex basal régime, while the overall geomorphic imprint, constrained by radiocarbon dates, has been used to reconstruct the retreat style and history of the palaeo-ice stream. Mapping of relict subglacial meltwater channels has revealed an intricate hydrological system characterised by multiple network types (cf. Anderson & Oakes-Fretwell, 2008) that are strongly dependent on the underlying substrate and which show progressive organisation seaward. Grounding zone wedges (GZWs), formed by the subglacial transport and then deposition of deformation till at the grounding-line during still-stands (Alley et al. 1989), are well documented, yet poorly understood phenomena. We present evidence of four previously unreported GZWs on the outer continental shelf of Marguerite Bay occuring within a zone that has undergone catastrophic grounding line retreat (Kilfeather et al. 2010). This suggests that GZWs can form relatively rapidly, while the localised nature and close association of these features with mega-scale glacial lineations is in keeping with a dynamic sedimentary system characterised by hierarchies of sediment transport. Preliminary modelling results are also presented that use the geomorphological evidence to constrain numerical simulations of the Marguerite Bay palaeo-ice stream system. Modelling output is then compared with both the known retreat style as recorded by geomorphological mapping and the deglacial chronology.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.C51B..05L
- Keywords:
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- 0730 CRYOSPHERE / Ice streams;
- 0758 CRYOSPHERE / Remote sensing;
- 0798 CRYOSPHERE / Modeling