Geomorphology and shallow sub-sea-floor structures underneath the Ekström Ice Shelf, Antarctica

Oetting, A. et al. (2022) Geomorphology and shallow sub-sea-floor structures underneath the Ekström Ice Shelf, Antarctica. Cryosphere, 16(5), pp. 2051-2066. (doi: 10.5194/tc-16-2051-2022)

Abstract

The Ekström Ice Shelf is one of numerous small ice shelves that fringe the coastline of western Dronning Maud Land, East Antarctica. Reconstructions of past ice-sheet extent in this area are poorly constrained, due to a lack of geomorphological evidence. Here, we present a compilation of geophysical surveys in front of and beneath the Ekström Ice Shelf, to identify and interpret evidence of past ice-sheet flow, extent and retreat. The sea floor beneath the Ekström Ice Shelf is dominated by an incised trough, which extends from the modern-day grounding line onto the continental shelf. Our surveys show that mega-scale glacial lineations cover most of the mouth of this trough, terminating 11 km away from the continental shelf break, indicating the most recent minimal extent of grounded ice in this region. Beneath the front ∼30 km of the ice shelf measured from the ice shelf edge towards the inland direction, the sea floor is characterised by an acoustically transparent sedimentary unit, up to 45 m thick. This is likely composed of subglacial till, further corroborating the presence of past grounded ice cover. Further inland, the sea floor becomes rougher, interpreted as a transition from subglacial tills to a crystalline bedrock, corresponding to the outcrop of the volcanic Explora Wedge at the sea floor. Ice retreat in this region appears to have happened rapidly in the centre of the incised trough, evidenced by a lack of overprinting of the lineations at the trough mouth. At the margins of the trough uniformly spaced recessional moraines suggest ice retreated more gradually. We estimate the palaeo-ice thickness at the calving front around the Last Glacial Maximum to have been at least 305 to 320 m, based on the depth of iceberg ploughmarks within the trough and sea level reconstructions. Given the similarity of the numerous small ice shelves along the Dronning Maud Land coast, these findings are likely representative for other ice shelves in this region and provide essential boundary conditions for palaeo ice-sheet models in this severely understudied region.

• Item Type: Articles
• Additional Information: Financial support. Fieldwork and data processing by ECS since 2016 were funded through the AWI-BGR Sub-EIS-Obs project. ECS was additionally partly funded through the DFG COST-S2S project grant EI672/10-1 in the framework of the priority program “Antarctic Research with comparative investigations in Arctic ice areas”. Fieldwork was supported by the large-scale research infrastructure Neumayer III and Polarstern (Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 2016, 2017). RD was supported by an Emmy Noether Grant of the Deutsche Forschungsgemeinschft (DR 822/3-1).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ehlers, Professor Todd A.
• Authors: Oetting, A., Smith, E. C., Arndt, J. E., Dorschel, B., Drews, R., Ehlers, T. A., Gaedicke, C., Hofstede, C., Klages, J. P., Kuhn, G., Lambrecht, A., Läufer, A., Mayer, C., Tiedemann, R., Wilhelms, F., and Eisen, O.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Cryosphere
• Publisher: Copernicus Publications on behalf of the European Geosciences Union
• ISSN: 1994-0424
• ISSN (Online): 1994-0424
• Copyright Holders: Copyright © 2022 The Authors
• First Published: First published in Cryosphere 16:2051–2066
• Publisher Policy: Reproduced under a Creative Commons licence