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.
Highlights
In the western Dronning Maud Land sector of East Antarctica, the area between the Riiser Larsen and Vigrid ice shelves, ice drains through numerous small ice shelves from a combined drainage area of ∼470,000 km2 (Rignot et al, 2013)
We have identified a diverse range of landforms beneath and in front of the Ekström Ice Shelf (EIS) using a combination of geophysical methods: swath bathymetry, sub-bottom profiler and seismic reflection data
At the trough mouth we have identified mega-scale glacial lineations (MSGLs), confirming that this trough was likely occupied by a palaeo-ice stream
Summary
In the western Dronning Maud Land (wDML) sector of East Antarctica (see Fig. 1a), the area between the Riiser Larsen and Vigrid ice shelves, ice drains through numerous small ice shelves from a combined drainage area of ∼470,000 km (Rignot et al, 2013). The glacial history of this region is poorly constrained and limits our ability to understand past responses of this sector to climatic and oceanic variations. This is essential for evaluating future ice-sheet development in this sector of East Antarctica. The continental shelf in this area is narrow (Arndt et al, 35 2013) and is largely covered by thick ice shelves, preventing ship-based data acquisition. Autonomous underwater vehicles (AUVs) provide one solution to collect high resolution bathymetry data of sub-ice shelf sea floor structures (e.g. Jenkins et al, 2010; Davies et al, 2017).
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