Streaming flow of an Antarctic Peninsula palaeo-ice stream, both by basal sliding and deformation of substrate

Abstract

Acoustic sub-bottom profiler surveys on the northeast Antarctic Peninsula shelf indicate that parts of the seabed are underlain by an acoustically transparent layer that is thin on the inner shelf and becomes thicker and more extensive towards the outer shelf. Sedimentological and geophysical data are combined to construct a bed model where streaming ice flow, by both deformation and basal sliding, took place within cross-shelf troughs. The model suggests only limited deformation contributed to fast flow on the inner shelf, i.e. in the onset zone of ice streaming, where the bed was predominantly underlain by a stiff till. Thus, fast ice flow in this area might have been by basal sliding, with deformation confined to discontinuous patches of soft till <40 cm thick. Towards the middle and outer shelf, extensive, thick sequences of soft till suggest a change in the dominant subglacial process towards widespread deformation. This downstream change from basal sliding to subglacial deformation is manifest in the transition from stiff-till dominance to soft-till dominance, while a downstream increase in ice flow velocity is evident from the complex geomorphic imprint on the inner shelf evolving to the more restricted set of bedforms on the outer shelf.

Configuration of the Northern Antarctic Peninsula Ice Sheet at LGM based on a new synthesis of seabed imagery

“…The Cryosphere, 9, 613-629, 2015 www.the-cryosphere.net/9/613/2015/ (Reinardy et al, 2011). One hypothesis, therefore, would suggest that the divergence of flow was related to faster flow and was funneled out of the inner Larsen B embayment by a bed that was more easily deformed (mud base) than the higher friction of the sandy volcaniclastic palagonite units that comprise the Seal Nunatak massif.…”

Thin-layer effects in glaciological seismic amplitude-versus-angle (AVA) analysis: implications for characterising a subglacial till unit, Russell Glacier, West Greenland

“…Although glaciers themselves are clearly good approximations to half-spaces, subglacial tills frequently contain metre-(or sub-metre-) scale contrasts (Smith, 2007), such as the transitional boundaries between dilatant and lodged till (e.g. Clarke et al, 1984;Echelmeyer and Wang, 1987;Iverson et al, 1988Iverson et al, , 1994Truffer et al, 2001;Boulton et al, 2001;Porter and Murray, 2001;Evans et al, 2006;Iverson, 2011;Reinardy et al, 2011). It would therefore be prudent to consider how thin layering affects a seismic AVA response whenever surveys are conducted over till substrates.…”

“…Measurements of the hardness of previously-glaciated surfaces have also been used to inform palaeo-flow reconstructions (e.g. Reinardy et al, 2011).…”

Antarctic palaeo-ice streams

“…East Antarctic Peninsula, has also been associated with a change in basal processes (from 327 9 basal sliding to deformation) and an increase in ice velocity (Reinardy et al 2011b The geometry of the basal reflector underlying the acoustically transparent unit ranges from 363 smooth and flat to irregular and undulating ( shelf (Pudsey et al 1994Licht et al 1996Licht et al , 1998Licht et al , 1999 between this bedrock and unconsolidated sediment further out on the shelf (Fig. 4c and Table 493 3) (Anderson et al 2001; Camerlenghi et al 2001;Wellner et al 2001Wellner et al , 2006; Canals et al …”

“…Such differences are an 287 important consideration when attempting to predict the future behaviour of ice streams in 288 Greenland and Antarctica and, undoubtedly, add considerable complexity when attempting to 289 model the behaviour of ice streams and resolve subglacial topography in ice sheet models. East Antarctic Peninsula, has also been associated with a change in basal processes (from 327 basal sliding to deformation) and an increase in ice velocity (Reinardy et al 2011b speculate about these processes from the palaeo-ice stream records.…”