Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing
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We use borehole optical televiewing (OPTV) to explore the internal structure of Larsen C Ice Shelf (LCIS). We report a suite of five ~90 m long OPTV logs, recording a light-emitting diode-illuminated, geometrically correct image of the borehole wall, from the northern and central sectors of LCIS collected during austral spring 2014 and 2015. We use a thresholding-based technique to estimate the refrozen ice content of the ice column and exploit a recently calibrated density-luminosity relationship to reveal its structure. All sites are dense and strongly influenced by surface melt, with frequent refrozen ice layers and mean densities, between the depths of 1.87 and 90 m, ranging from 862 to 894 kg m−3. We define four distinct units that comprise LCIS and relate these to ice provenance, dynamic history, and past melt events. These units are in situ meteoric ice with infiltration ice (U1), meteoric ice which has undergone enhanced densification (U2), thick refrozen ice (U3), and advected continental ice (U4). We show that the OPTV-derived pattern of firn air content is consistent with previous estimates, but that a significant proportion of firn air is contained within U4, which we interpret to have been deposited inland of the grounding line. The structure of LCIS is strongly influenced by the E-W gradient in föhn-driven melting, with sites close to the Antarctic Peninsula being predominantly composed of refrozen ice. Melting is also substantial toward the ice shelf center with >40% of the overall imaged ice column being composed of refrozen ice.
Ashmore , D W , Hubbard , B , Luckman , A , Kulessa , B , Bevan , S , Booth , A , Munneke , P K , O'Leary , M , Sevestre , H & Holland , P R 2017 , ' Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing ' Journal of Geophysical Research - Earth Surface , vol 122 , no. 5 , pp. 1139-1153 . DOI: 10.1002/2016JF004047
Journal of Geophysical Research - Earth Surface
© 2017 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Research was funded by the UK Natural Environmental Research Council grants NE/L006707/1 and NE/L005409/1 and a HEFCW/Aberystwyth University Capital Equipment Grant to B.H. Data will be available via the project website (www.projectmidas.org) and the UK Polar Data Centre (https://www.bas.ac.uk/data/uk-pdc/) from mid-2017.
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