Abstract
Abstract. Quantitative satellite observations only provide an assessment of ice sheet mass loss over the last four decades. To assess long-term drivers of ice sheet change, geological records are needed. Here we present the first millennial-scale reconstruction of David Glacier, the largest East Antarctic outlet glacier in Victoria Land. To reconstruct changes in ice thickness, we use surface exposure ages of glacial erratics deposited on nunataks adjacent to fast-flowing sections of David Glacier. We then use numerical modelling experiments to determine the drivers of glacial thinning. Thinning profiles derived from 45 10Be and 3He surface exposure ages show David Glacier experienced rapid thinning of up to 2 m/yr during the mid-Holocene (∼ 6.5 ka). Thinning slowed at 6 ka, suggesting the initial formation of the Drygalski Ice Tongue at this time. Our work, along with ice thinning records from adjacent glaciers, shows simultaneous glacier thinning in this sector of the Transantarctic Mountains occurred 4–7 kyr after the peak period of ice thinning indicated in a suite of published ice sheet models. The timing and rapidity of the reconstructed thinning at David Glacier is similar to reconstructions in the Amundsen and Weddell embayments. To identify the drivers of glacier thinning along the David Glacier, we use a glacier flowline model designed for calving glaciers and compare modelled results against our geological data. We show that glacier thinning and marine-based grounding-line retreat are controlled by either enhanced sub-ice-shelf melting, reduced lateral buttressing or a combination of the two, leading to marine ice sheet instability. Such rapid glacier thinning events during the mid-Holocene are not fully captured in continental- or catchment-scale numerical modelling reconstructions. Together, our chronology and modelling identify and constrain the drivers of a ∼ 2000-year period of dynamic glacier thinning in the recent geological past.
Highlights
Since the Last Glacial Maximum (LGM), ice sheets retreated in both hemispheres, causing a sea-level rise of ∼ 130 m (Clark et al, 2009)
Ice sheet retreat continued into the Holocene (11.7 ka–present), and global sea level stabilised at near pre-industrial levels by 6– 7 ka (Bentley et al, 2014; Lambeck et al, 2014)
To simulate the natural variability that might be expected in an ocean forcing record, we apply a fluctuation of up to 0.5 m/yr magnitude using a random noise generator, and this variation is added on top of the 500-year increase in forcing that is already applied. It is not the intention of these sensitivity experiments to reproduce the exact timing of marine-based grounding-line retreat along the David Glacier, but rather we aim to explore the range of possible drivers that would enable the overall scale of retreat observed between the LGM and present day
Summary
Since the Last Glacial Maximum (LGM), ice sheets retreated in both hemispheres, causing a sea-level rise of ∼ 130 m (Clark et al, 2009). This period, the last glacial termination, represents Earth’s last major period of climate warming, between ∼ 20 and 11.7 ka (Denton et al, 2010). Ice sheet thinning and retreat was rapid at times, potentially contributing to periods of rapid sea-level rise (Weber et al, 2014). Discovered by the British National Antarctic Expedition (1901– 1904), David Glacier drains the East Antarctic Ice Sheet (EAIS), traverses and incises the Transantarctic Mountains (TAM), and discharges into the western Ross Sea as the floating Drygalski Ice Tongue Improved understanding of the timing and the processes that caused deglaciation help us to better understand the processes driving observed mass loss in parts of Antarctica today
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