Preprints
https://doi.org/10.5194/tc-2021-305
https://doi.org/10.5194/tc-2021-305

  14 Oct 2021

14 Oct 2021

Review status: this preprint is currently under review for the journal TC.

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

Astrid Oetting1,a, Emma C. Smith1,b, Jan Erik Arndt1, Boris Dorschel1, Reinhard Drews2, Todd A. Ehlers2, Christoph Gaedicke3, Coen Hofstede1, Johann P. Klages1, Gerhard Kuhn1, Astrid Lambrecht4, Andreas Läufer3, Christoph Mayer4, Ralf Tiedemann1,5, Frank Wilhelms1,6, and Olaf Eisen1,5 Astrid Oetting et al.
  • 1Geosciences, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 2Department of Geoscience, University of Tübingen, Tübingen, Germany
  • 3BGR, Federal Institute for Geoscience and Natural Resources, Hannover, Germany
  • 4Geodesy and Glaciology, Bavarian Academy of Science and Humanities, Munich, Germany
  • 5Department of Geoscience, University of Bremen, Bremen, Germany
  • 6Department of Geoscience, University of Göttingen, Göttingen, Germany
  • anow at: Institut für Planetologie, Westfälische-Wilhelms Universität, Münster, Germany
  • bnow at: School of Earth and Environment, University of Leeds, Leeds, UK

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 on to 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 maximal extent of grounded ice in this region. Beneath the front ~30 km of the ice shelf, 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 m 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 around 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.

Astrid Oetting et al.

Status: open (until 09 Dec 2021)

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Astrid Oetting et al.

Astrid Oetting et al.

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Short summary
This study combines a variety of geophysical measurements in front of and beneath the Ekström Ice Shelf in order to identify and interpret geomorphological evidences of past ice sheet flow, extent and retreat. The maximal extent of grounded ice in this region was 11 km away from the continental shelf break. The thickness of palaeo-ice on the calving front around the LGM was estimated to be at least 305 m to 320 m. We provide essential boundary conditions for palaeo ice-sheet models.