New insights into the formation of submarine glacial landforms from high-resolution Autonomous Underwater Vehicle data

Christine L Batchelor,Aleksandr Montelli,Dag Ottesen,Jeffrey Evans,Evelyn K Dowdeswell,Frazer D.W Christie,Julian A Dowdeswell

doi:10.1016/j.geomorph.2020.107396

Christine L Batchelor, Aleksandr Montelli + Show 5 more

Open Access

https://doi.org/10.1016/j.geomorph.2020.107396

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Abstract

Autonomous Underwater Vehicles (AUVs) deployed close to the seafloor can acquire high-resolution geophysical data about the topography and shallow stratigraphy of the seabed, yet have had limited application within the fields of glacial geomorphology and ice sheet reconstruction. Here, we present multibeam echo-sounding, side-scan sonar, sub-bottom profiler and High-Resolution Synthetic Aperture Sonar (HISAS) data acquired during three AUV dives on the northeast Antarctic Peninsula continental shelf. These data enable glacial landforms, including mega-scale glacial lineations (MSGLs), grounding-zone wedges (GZWs) and iceberg ploughmarks, to be imaged at a horizontal resolution of a few tens of centimetres, allowing for the identification of subtle morphological features. We map tidal ridges that are interpreted as having been formed 1) along the ice-sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles, and 2) by the tidally driven motion of grounded or near-grounded icebergs. These data also enable the mapping of small GZWs that show the location of short-term still-stands or re-advances of the ice-sheet grounding zone. No meltwater channels are identified from our data, suggesting that free-flowing meltwater may not be essential for the formation of GZWs or MSGLs. The examples presented here show how high-resolution AUV-derived geophysical data provide a step-change in our ability to image seafloor glacial landforms, enabling new interpretations about past ice dynamics and glacial sedimentation at fine temporal and spatial scales.

Highlights

The analysis of glacial landforms preserved on and beneath the seafloor of formerly glaciated continental margins provides information about the past dynamic behaviour of glaciers and ice sheets (e.g. Dowdeswell et al, 2008a, 2016; Greenwood et al, 2012) and the mechanisms by which sediment is eroded, transported and deposited by ice (e.g. Lowe and Anderson, 2003; Dowdeswell et al, 2004; Spagnolo et al, 2014)
We present high-resolution Autonomous Underwater Vehicles (AUVs)-acquired geophysical data of landforms from formerly subglacial, ice-marginal and proglacial environments on the NE Atlantic Peninsula continental shelf (Fig. 1)
Trough on High-Resolution Synthetic Aperture Sonar (HISAS)-derived bathymetry (Fig. 3a–d). These ridges are interpreted as mega-scale glacial lineations (MSGLs) (e.g. Stokes and Clark, 2002; Dowdeswell et al, 2004; King et al, 2009; Spagnolo et al, 2014) that were formed beneath an ice stream that extended through

Summary

Introduction

The analysis of glacial landforms preserved on and beneath the seafloor of formerly glaciated continental margins provides information about the past dynamic behaviour of glaciers and ice sheets (e.g. Dowdeswell et al, 2008a, 2016; Greenwood et al, 2012) and the mechanisms by which sediment is eroded, transported and deposited by ice (e.g. Lowe and Anderson, 2003; Dowdeswell et al, 2004; Spagnolo et al, 2014). The analysis of glacial landforms preserved on and beneath the seafloor of formerly glaciated continental margins provides information about the past dynamic behaviour of glaciers and ice sheets Submarine glacial 44 landforms are typically mapped using geophysical data acquired from hull-mounted sonar systems. The acquisition of high-resolution geophysical data is necessary to examine complexities in ice-sheet behaviour recorded in seafloor geomorphology. High-frequency sonar systems provide information about the seafloor and subsurface at a higher spatial resolution compared with lowerfrequency sonar, albeit with a shorter vertical range. Geophysical data collected from AUVs can, be of significantly higher horizonal resolution (often < 1 metre) compared with data collected from conventional, hull-mounted sonar systems (typically several metres or tens of metres), they are typically acquired over narrower swaths of the seafloor. AUVs have been used extensively by the hydrocarbon industry and in marine archaeological studies (Bingham et al, 2010; Bates et al, 2011; Ødegård et al, 2018), they have hitherto had limited application within the field of glacial geomorphology (Dowdeswell et al, 2008b, 2020a; Graham et al, 2013; Howe et al., 2019)

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