Abstract
Detailed bathymetric and sub-bottom acoustic observations in Bourgeois Fjord (Marguerite Bay, Antarctic Peninsula) provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle. Submarine landforms observed in the 50 km-long fjord, from the margins of modern tidewater glaciers to the now ice-distal Marguerite Bay, are described and interpreted. The landforms are grouped into four morpho-sedimentary systems: (i) glacial advance and full-glacial; (ii) subglacial and ice-marginal meltwater; (iii) glacial retreat and neoglaciation; and (iv) Holocene mass-wasting. These morpho-sedimentary systems have been integrated with morphological studies of the Marguerite Bay continental shelf and analysed in terms of the specific sedimentary processes and/or stages of the glacial cycle. They demonstrate the action of an ice-sheet outlet glacier that produced drumlins and crag-and-tail features in the main and outer fjord. Meltwater processes eroded bedrock channels and ponds infilled by fine-grained sediments. Following the last deglaciation of the fjord at about 9000 yr BP, subsequent Holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in Blind Bay. Recent stillstands and/or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization, probably during the Little Ice Age, and a series of smaller landforms that reveal intermittent minor readvances. Mass-wasting processes also affected the walls of the fjord and produced scars and fan-shaped deposits during the Holocene. Glacier-terminus changes during the last six decades, derived from satellite images and aerial photographs, reveal variable behaviour of adjacent tidewater glaciers. The smaller glaciers show the most marked recent retreat, influenced by regional physiography and catchment-area size.
Highlights
The geomorphology of glaciated continental margins contains records of environmental history and of the geological processes shaping the seafloor (e.g. Anderson, 1999; Ó Cofaigh et al, 2002; Ottesen et al, 2005)
This paper investigates the submarine landform record in Bourgeois Fjord, providing evidence for the glacial dynamics in the area from the termini of tidewater glaciers to the more open marine environment of Marguerite Bay
A succession of landforms with increased elongation ratios on the mid-shelf marks the transition from crystalline bedrock, where subglacial meltwater channels are incised, to sedimentary bedrock (Ó Cofaigh et al, 2005; Anderson and Fretwell, 2008; Livingstone et al, 2013, 2016)
Summary
The geomorphology of glaciated continental margins contains records of environmental history and of the geological processes shaping the seafloor (e.g. Anderson, 1999; Ó Cofaigh et al, 2002; Ottesen et al, 2005). The increasing resolution of geophysical and geological datasets acquired from high-latitude shelves and fjords is providing new insights into the major processes occurring during the last full-glacial and deglacial periods in particular (Dowdeswell and Ó Cofaigh, 2002; Jakobsson et al, 2008). The assessment of models for predicting the future evolution of ice masses requires a knowledge of past ice dynamics and, in particular, studies of the styles of deglaciation for the last glacial cycle, that depend on a complex interplay between global and local factors (Livingstone et al, 2012). Mass balance models for outlet glaciers highlight the influence of glacier dynamics on climate and global sea-level (Kaser et al, 2006) and, in the case of tidewater glaciers, processes involving iceberg discharge are important but poorly known contributors to mass loss from ice caps (Dowdeswell et al, 2008a; Radić and Hock, 2011)
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