Abstract

Understanding past retreat of Antarctic ice margins provides valuable insight for predicting how ice sheets may respond to future environmental change. This study, based on high resolution multibeam bathymetry from the nearshore region of the Windmill Islands, East Antarctica, reveals a style of retreat that has been rarely observed on the Antarctic margin. A suite of seafloor features record the final retreat stages of a relatively thin, and increasingly fractured tidewater glacier confined within narrow troughs and embayments, forming a suite of features more typical of warm-based ice, but occurring here in a region of cold-based ice with limited surface meltwater production. The pattern of moraines and crevasse squeeze ridges, reveals strong topographic and substrate control on the nature of ice sheet retreat. Topographic control is indicated by fine-scale variability in the orientation and distribution of glacial landforms, which show that the seabed topography influenced the shape of the ice margin, caused deflection of ice flow and led to the separation of flow downstream from topographic highs. The availability of water saturated marine sediments within the troughs and depressions also had a profound effect on the landform record, facilitating the construction of moraines and crevasse squeeze ridges within topographic lows, corresponding to areas of modern sediment accumulation. Surrounding areas of crystalline bedrock, by contrast, acted as sticky spots and lack a well-developed landform record. This seafloor glacial record emphasises the importance of understanding the bed topography and substrate when predicting the nature of ice margin retreat and provides new perspectives for understanding the stability of the East Antarctic margin.

Highlights

  • Features revealed by high resolution multibeam mapping on glaciated margins are increasingly providing new insights into the processes, behaviour and patterns of ice margin advance and retreat over glacial and interglacial cycles on the Antarctic 25 margin (e.g. Anderson et al, 2001; Fernandez et al, 2018; Halberstadt et al, 2016; Heroy and Anderson, 2005; Jakobsson et al, 2012; Livingstone et al, 2013; Wellner et al, 2001; Wellner et al, 2006), and ice sheet response to Holocene climate variability in Antarctic (e.g. García et al, 2016; Munoz and Wellner, 2018) and other glacial settings (e.g. Dowdeswell et al, 2016; Dowdeswell and Vásquez, 2013; Ottesen and Dowdeswell, 2009)

  • Topographic control is indicated by finescale variability in the orientation and distribution of glacial landforms, which show that the seabed topography influenced the 15 shape of the ice margin, caused deflection of ice flow and led to the separation of flow downstream from topographic highs

  • 120 Moraines vary in shape from linear to rectilinear, arcuate, hairpinned and irregular forms, according to changes in the local bed topography and structure of the ice sheet margin

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Summary

Introduction

Features revealed by high resolution multibeam mapping on glaciated margins are increasingly providing new insights into the processes, behaviour and patterns of ice margin advance and retreat over glacial and interglacial cycles on the Antarctic 25 margin (e.g. Anderson et al, 2001; Fernandez et al, 2018; Halberstadt et al, 2016; Heroy and Anderson, 2005; Jakobsson et al, 2012; Livingstone et al, 2013; Wellner et al, 2001; Wellner et al, 2006), and ice sheet response to Holocene climate variability in Antarctic (e.g. García et al, 2016; Munoz and Wellner, 2018) and other glacial settings (e.g. Dowdeswell et al, 2016; Dowdeswell and Vásquez, 2013; Ottesen and Dowdeswell, 2009). Antarctic ice sheet that are grounded below sea level on reverse-sloping beds. Ice sheets in these settings are vulnerable to rapid retreat due to sub-glacial marine incursion, causing marine ice sheet instability (Bindschadler, 2006; Schoof, 2007). Airborne geophysical surveys over the East Antarctic Ice Sheet (EAIS) have confirmed the correlation between thick marine sedimentary basins and areas of high ice flow rates (e.g. Aitken et al, 2014; Bamber et al, 2006; Ferraccioli et al, 2009). Carson et al (2017) provided evidence of expansion of the Law Dome ice margin onto the East Antarctic continental shelf leaving behind a complex record of glacial geomorphological features preserved on the seafloor. Terrestrial research suggests a mid- to late Holocene readvance of the Law

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