Controls on Mid-Holocene Thinning along David Glacier, Antarctica

Abstract:

David Glacier is one of the largest glaciers in the world, draining an area of the East Antarctic Ice Sheet roughly the size of New Zealand or Great Britain. However, until now we knew little about its onshore pre-historic behaviour and controls. Here we present the first millennial-scale reconstruction of David Glacier for the Holocene. Thinning profiles derived from 21 ¹⁰Be coherent surface exposure ages show that David Glacier experienced rapid thinning up to 2 m/yr ~6,500 years ago. Thinning stabilised at 6 kyr, suggesting initial formation of the floating extension of David Glacier, the Drygalski Ice Tongue, at this time.

In order to identify the potential controls on these rapid changes along the David Glacier, we use an outlet glacier/ice shelf flow line model to compare modelled results against our geological data. We show that glacier thinning and marine-based grounding line retreat is initially sensitive to small increases in sub-ice shelf melting and reduced lateral buttressing, leading to Marine Ice Sheet Instability. Once pinned to a prominent sill at the mouth of the David Fjord, elevated sub-ice shelf melting, a decoupling from surrounding coastal ice and a deep fjord (~1500 mbsl) leads to a rapid onshore thinning and grounding line retreat ~50 km inland. Such rapid glacier thinning events at this time are not captured in continental or sector-scale numerical modelling reconstructions. Together, our chronology and modelling results suggest a ~2,000 year period of dynamic thinning in the recent geological past, which may offer insights into future evolution of the Antarctic Ice Sheet.