Mid-Holocene thinning of David Glacier, Antarctica: Chronology and Controls

Abstract

Abstract. Quantitative satellite observations provide a comprehensive assessment of ice sheet mass loss over the last four decades, but limited insights into long-term drivers of ice sheet change. Geological records can extend the observational record and aid our understanding of ice sheet–climate interactions. Here we present the first millennial-scale reconstruction of David Glacier, the largest East Antarctic outlet glacier in Victoria Land. We use surface exposure dating of glacial erratics deposited on nunataks to reconstruct changes in ice surface elevation through time. 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 that David Glacier experienced rapid thinning up to 2 m/yr during the mid-Holocene (~ 6,500 years ago). Thinning stabilised at 6 kyr, suggesting initial formation of the Drygalski Ice Tongue at this time. Our work, along with terrestrial cosmogenic nuclide records from adjacent glaciers, shows simultaneous glacier thinning in this sector of the Transantarctic Mountains occurred ~ 3 kyr after the retreat of marine-based grounded ice in the western Ross Embayment. The timing and rapidity of the reconstructed thinning at David Glacier is similar to reconstructions in the Amundsen and Weddell embayments. In order to identify the potential causes of these rapid changes along the David Glacier, we use a glacier flow line model designed for calving glaciers and compare modelled results against our geological data. We show that glacier thinning and marine-based grounding line retreat is initiated by interactions between enhanced sub-ice shelf melting and reduced lateral buttressing, leading to Marine Ice Sheet Instability. Such rapid glacier thinning events are not captured in continental or sector-scale numerical modelling reconstructions for this period. Together, our chronology and modelling suggest a ~ 2,000-year period of dynamic thinning in the recent geological past.

Holocene thinning of Darwin and Hatherton glaciers, Antarctica, and implications for grounding-line retreat in the Ross Sea

“…These ages confirm and extend the thinning chronology given by the 10 Be exposure ages. The exposure ages in this transect are too young to record but do not preclude a large Early Holocene deglaciation event, as found at Beardmore, Mackay, Mawson, and David glaciers (Jones et al, 2015Spector et al, 2017;Stutz et al, 2020). However, those glaciers only thinned by tens of meters near the glacier mouth following a large drawdown of several hundred meters in the Early Holocene, whereas Darwin Glacier thinned by 200 m since 6.7 ka, a history more similar to that at Reedy Glacier (Todd et al, 2010).…”

“…Above this, bedrock becomes significantly more weathered, and surfaces are largely devoid of transported boulders and cobbles. The geomorphic transition from surfaces shaped by wet-based glaciation at low altitude to heavily weathered upper slopes resembles transects on other peaks in the TAM and Marie Byrd Land (e.g., Sugden et al, 2005). We attribute the geomorphic transition to differential erosion during the LGM and earlier glaciations.…”

“…More recent data show that the ∼ 800 km long section of the Transantarctic Mountains (TAM) front between Terra Nova Bay and Shackleton Glacier may have deglaciated almost simultaneously in the Early to Mid-Holocene, followed by slow recession into the Late Holocene (Spector et al, 2017). Lower Shackleton and Beardmore glaciers had reached their modern configurations by 7.4 ka, roughly contemporaneous with dramatic thinning at Mackay, Mawson, and David glaciers (Jones et al, 2015Stutz et al, 2020) and ungrounding of ice in McMurdo Sound . The pattern of deglaciation was complex, as the grounding line temporarily stabilized on pinning points and retreated in deep troughs (Dowdeswell et al, 2008;Halberstadt et al, 2016;Prothro et al, 2020).…”

Nunataks as barriers to ice flow: implications for palaeo ice-sheet reconstructions

“…to assess the model's ability to reproduce the geological record). In light of our results, it is understandable that experiments using a regular grid at these resolutions struggle to closely match ice surface elevation over mountainous regions reconstructed from cosmogenic exposure dating, and do not fully capture their recorded timing and magnitude of ice thinning (Spector et al, 2019;Stutz et al, 2020). In our experiments, a grid-cell size smaller than the glacier width manages to capture the drainage effect to some degree.…”

“…Ice sheet models currently struggle to replicate the timing, magnitude, and rate of ice thickness change that has been inferred from field studies (Jones et al, 2020;Stutz et al, 2020). This may be partly due to the spatial resolution of these models which, when run over glacial-interglacial cycles, do not resolve the pattern of ice flow around individual nunataks, and consequently cannot resolve the transient response of the ice surface at the sampled locations.…”