Abstract
AbstractWe 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.
Highlights
Ice shelves fringe much of Antarctica and are sensitive indicators of environmental changes owing to their low elevation, low latitude, and exposure to both oceanic and atmospheric forcings
We show that the optical televiewing (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 ice shelf density structure has been reconstructed based on OPTV image luminosity and the refrozen melt portion based on application of a quantitative thresholding technique
Summary
Ice shelves fringe much of Antarctica and are sensitive indicators of environmental changes owing to their low elevation, low latitude, and exposure to both oceanic and atmospheric forcings. Ice shelves form when glaciers and ice streams flowing across the grounding line begin to float and spread laterally to fill an embayment. Once established by this core of continental ice, they are able to gain and lose mass at their upper and lower interfaces, as well as calving at the marine margin. Where ice shelves have thinned or collapsed, inflowing glaciers have accelerated and their discharge has increased [e.g., Paolo et al, 2015; De Rydt et al, 2015; Scambos et al, 2004]
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